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LTC4088 High Efficiency Battery Charger/USB Power Manager FEATURES
DESCRIPTIO

Switching Regulator Makes Optimal Use of Limited Power Available from USB Port to Charge Battery and Power Application 180m Internal Ideal Diode Plus Optional External Ideal Diode Controller Seamlessly Provides Low Loss Power Path When Input Power is Limited or Unavailable Full Featured Li-Ion/Polymer Battery Charger VBUS Operating Range: 4.25V to 5.5V (7V Absolute Maximum--Transient) 1.2A Maximum Input Current Limit 1.5A Maximum Charge Current with Thermal Limiting Bat-TrackTM Adaptive Output Control Slew Control Reduces Switching EMI Low Profile (0.75mm) 14-Lead 4mm x 3mm DFN Package
The LTC(R)4088 is a high efficiency USB PowerPathTM controller and Li-Ion/Polymer battery charger. It includes a synchronous switching input regulator, a full-featured battery charger and an ideal diode. Designed specifically for USB applications, the LTC4088's switching regulator automatically limits its input current to either 100mA, 500mA or 1A for wall-powered applications via logic control. The switching input stage provides power to VOUT where power sharing between the application circuit and the battery charger is managed. Unlike linear PowerPath controllers, the LTC4088's switching input stage can use nearly all of the 0.5W or 2.5W available from the USB port with minimal power dissipation. This feature allows the LTC4088 to provide more power to the application and eases thermal issues in space-constrained applications. An ideal diode ensures that system power is available from the battery when the input current limit is reached or if the USB or wall supply is removed. The LTC4088 is available in the low profile 14-Lead 4mm x 3mm x 0.75mm DFN surface mount package.
, LTC and LT are registered trademarks of Linear Technology Corporation. PowerPath and Bat-Track are trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents, including 6522118
APPLICATIO S

Media Players Digital Cameras GPS PDAs Smart Phones
TYPICAL APPLICATIO
WALL
High Efficiency Battery Charger/USB Power Manager
100 3.3H SYSTEM LOAD 90 80 EFFICIENCY (%) 70 60 50 40 30
USB 10F
3.3V
VBUS SW VOUT D0 D1 GATE LTC4088 D2 BAT CHRG LDO3V3 CLPROG PROG C/X GND NTC 8.2 0.1F Li-Ion
10F
1F 2.94k 499
+
4088 TA01a
20 10
U
Switching Regulator Efficiency to System Load (POUT/PBUS)
BAT = 4.2V BAT = 3.3V 0 0.01 VBUS = 5V IBAT = 0mA 10x MODE 0.1 IOUT (A) 1
4088 TA01b
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LTC4088 ABSOLUTE
(Note 1)
AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW NTC CLPROG LDO3V3 D2 C/X PROG CHRG 1 2 3 4 5 6 7 15 14 D1 13 D0 12 SW 11 VBUS 10 VOUT 9 BAT 8 GATE
VBUS (Transient) t < 1ms, Duty Cycle < 1% .. -0.3V to 7V VBUS (Static), BAT, CHRG, NTC, D0, D1, D2.......................................................... -0.3V to 6V ICLPROG ....................................................................3mA IPROG, IC/X ................................................................2mA ILDO3V3 ...................................................................30mA ICHRG ......................................................................75mA IOUT .............................................................................2A ISW ..............................................................................2A IBAT .............................................................................2A Maximum Operating Junction Temperature .......... 125C Operating Temperature Range ................. -40C to 85C Storage Temperature Range................... -65C to 125C
DE PACKAGE 14-LEAD (4mm x 3mm) PLASTIC DFN TJMAX = 125C, JA = 37C/W EXPOSED PAD (PIN 15) IS GND, MUST BE SOLDERED TO PCB
ORDER PART NUMBER LTC4088EDE
DE PART MARKING 4088
Order Options Tape and Reel: Add #TR Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF Lead Free Part Marking: http://www.linear.com/leadfree/ Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
SYMBOL VBUS IBUS(LIM) PARAMETER Input Supply Voltage Total Input Current Input Power Supply
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VBUS = 5V, BAT = 3.8V, RCLPROG = 2.94k, unless otherwise noted.
CONDITIONS
MIN 4.35 92 445 815 0.32 1.6
TYP
MAX 5.5
UNITS V mA mA mA mA mA mA mA mA mA mA mA/mA mA/mA mA/mA mA/mA mA/mA mA mA mA mA mA V mV
1x Mode 5x Mode 10x Mode Low Power Suspend Mode High Power Suspend Mode 1x Mode 5x Mode 10x Mode Low Power Suspend Mode High Power Suspend Mode 1x Mode 5x Mode 10x Mode Low Power Suspend Mode High Power Suspend Mode 1x Mode, BAT = 3.3V 5x Mode, BAT = 3.3V 10x Mode, BAT = 3.3V Low Power Suspend Mode High Power Suspend Mode 1x, 5x, 10x Modes Suspend Modes

97 470 877 0.39 2.05 6 14 14 0.038 0.038 224 1133 2140 11.3 59.4 135 672 1251 0.4 2.04 1.188 100
100 500 1000 0.50 2.5
IBUSQ (Note 4)
Input Quiescent Current
hCLPROG (Note 4) Ratio of Measured VBUS Current to CLPROG Program Current
IOUT
VOUT Current Available Before Discharging Battery
0.26 1.6
0.41 2.46
VCLPROG
CLPROG Servo Voltage in Current Limit
2
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LTC4088 ELECTRICAL CHARACTERISTICS
SYMBOL VUVLO VDUVLO VOUT PARAMETER VBUS Undervoltage Lockout VBUS to BAT Differential Undervoltage Lockout VOUT Voltage
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VBUS = 5V, BAT = 3.8V, RCLPROG = 2.94k, unless otherwise noted.
CONDITIONS Rising Threshold Falling Threshold Rising Threshold Falling Threshold 1x, 5x, 10x Modes, 0V < BAT 4.2V, IOUT = 0mA, Battery Charger Off USB Suspend Modes, IOUT = 250A 3.5 4.5 1.8 MIN 3.95 TYP 4.30 4.00 200 50 BAT + 0.3 4.6 2.25 0.18 0.30 1x, 5x Modes 10x Mode 2 3 15 4.179 4.165 980 192 4.200 4.200 1030 206 3.5 4.221 4.235 1080 220 5 4.7 4.7 2.7 MAX 4.35 UNITS V V mV mV V V MHz A A V V mA mA A
fOSC RPMOS RNMOS IPEAK RSUSP Battery Charger VFLOAT ICHG IBAT
Switching Frequency PMOS On Resistance NMOS On Resistance Peak Inductor Current Clamp Suspend LDO Output Resistance BAT Regulated Output Voltage 0C TA 85C Constant-Current Mode Charge Current Battery Drain Current RPROG = 1k RPROG = 5k VBUS > VUVLO, PowerPath Switching Regulator On, Battery Charger Off, IOUT = 0A VBUS = 0V, IOUT = 0A (Ideal Diode Mode)
23 1.000 0.100 1031
35
A V V mA/mA
VPROG VPROG,TRKL hPROG VTRKL VTRKL VRECHRG tTERM tBADBAT IC/X VC/X hC/X VCHRG ICHRG RON_CHG TLIM
PROG Pin Servo Voltage PROG Pin Servo Voltage in Trickle Charge Ratio of IBAT to PROG Pin Current Trickle Charge Threshold Voltage Trickle Charge Hystersis Voltage Recharge Battery Threshold Voltage Safety Timer Termination Period Bad Battery Termination Time Battery Charge Current at Programmed End of Charge Indication C/X Threshold Voltage Battery Charge Current Ratio to C/X CHRG Pin Output Low Voltage CHRG Pin Input Current Battery Charger Power FET On-Resistance (Between VOUT and BAT) Junction Temperature in Constant Temperature Mode ICHRG = 5mA BAT = 4.5V, VCHRG = 5V IBAT = 200mA Threshold Voltage Relative to VFLOAT Timer Starts when VBAT = VFLOAT BAT < VTRKL RC/X = 1k RC/X = 5k -80 3.2 0.4 85 BAT Rising 2.7 BAT < VTRKL
2.85 135 -100 4.0 0.5 100 20 100 1031 65 0 0.18 110
3.0 -120 4.8 0.6 115
V mV mV Hour Hour mA mA mV mA/mA
100 1
mV A C
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LTC4088 ELECTRICAL CHARACTERISTICS
SYMBOL NTC VCOLD VHOT VDIS INTC Ideal Diode VFWD RDROPOUT IMAX VLDO3V3 ROL3V3 RCL3V3 VIL VIH IPD Forward Voltage Detection Internal Diode On Resistance, Dropout Diode Current Limit Regulated Output Voltage Open-Loop Output Resistance Closed-Loop Output Resistance Input Low Voltage Input High Voltage Static Pull-Down Current VPIN = 1V 1.2 2 0mA < ILDO3V3 < 25mA IOUT = 10mA VBUS = 0V, IOUT = 10mA IOUT = 200mA 2 3.1 3.3 25 3.6 0.4 3.4 15 2 0.18 mV mV A V V V A Cold Temperature Fault Threshold Voltage Hot Temperature Fault Threshold Voltage NTC Disable Threshold Voltage NTC Leakage Current Rising Threshold Hysteresis Falling Threshold Hysteresis Falling Threshold Hysteresis VNTC = VBUS = 5V 75.0 33.4 0.7 -50 76.5 1.5 34.9 1.5 1.7 50 78.0 36.4 2.7 50 %VBUS %VBUS %VBUS %VBUS %VBUS mV nA PARAMETER
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VBUS = 5V, BAT = 3.8V, RCLPROG = 2.94k, unless otherwise noted.
CONDITIONS MIN TYP MAX UNITS
Always On 3.3V Supply
Logic (D0, D1, D2)
Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: The LTC4088E is guaranteed to meet performance specifications from 0C to 85C. Specifications over the - 40C to 85C operating temperature range are assured by design, characterization and correlation with statistical process controls.
Note 3: The LTC4088E includes overtemperature protection that is intended to protect the device during momentary overload conditions. Junction temperature will exceed 125C when overtemperature protection is active. Continuous operation above the specified maximum operating junction temperature may impair device reliability. Note 4: Total input current is the sum of quiescent current, IBUSQ, and measured current given by VCLPROG/RCLPROG * (hCLPROG + 1)
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LTC4088 TYPICAL PERFOR A CE CHARACTERISTICS TA = 25C unless otherwise noted.
Ideal Diode V-I Characteristics
1.0 INTERNAL IDEAL DIODE WITH SUPPLEMENTAL EXTERNAL VISHAY Si2333 PMOS RESISTANCE () 0.25
0.8 CURRENT (A)
0.6 INTERNAL IDEAL DIODE ONLY 0.4
INTERNAL IDEAL DIODE 0.15
OUTPUT VOLTAGE (V)
0.2 VBUS = 0V VBUS = 5V 0 0 0.04 0.12 0.16 0.08 FORWARD VOLTAGE (V) 0.20
4088 G01
USB Limited Battery Charge Current vs Battery Voltage
700 600 CHARGE CURRENT (mA) 500 400 300 200 100 5x USB SETTING, BATTERY CHARGER SET FOR 1A 0 3.0 3.3 3.6 3.9 2.7 BATTERY VOLTAGE (V) CHARGE CURRENT (mA) VBUS = 5V RPROG = 1k RCLPROG = 2.94k 150 125 100 75 50 25 0 4.2
4088 G04
VBUS = 5V RPROG = 1k RCLPROG = 2.94k
BATTERY CURRENT (A)
PowerPath Switching Regulator Efficiency vs Output Current
100 90 EFFICIENCY (%) 80 70 60 50 40 0.01 VBAT = 3.8V 1x MODE 90 5x, 10x MODE 88 EFFICIENCY (%)
VBUS CURRENT (A)
0.1 OUTPUT CURRENT (A)
UW
1
4088 G07
Ideal Diode Resistance vs Battery Voltage
4.50
Output Voltage vs Output Current (Battery Charger Disabled)
VBAT = 4V VBUS = 5V 5x MODE
0.20
4.25
4.00 VBAT = 3.4V 3.75
0.10 INTERNAL IDEAL DIODE WITH SUPPLEMENTAL EXTERNAL VISHAY Si2333 PMOS
0.05
3.50
0 2.7
3.0
3.6 3.9 3.3 BATTERY VOLTAGE (V)
4.2
4088 G02
3.25
0
200
600 800 400 OUTPUT CURRENT (mA)
1000
4088 G03
USB Limited Battery Charge Current vs Battery Voltage
25
Battery Drain Current vs Battery Voltage
IOUT = 0A VBUS = 0V 20
15
10 VBUS = 5V (SUSPEND MODE)
5 1x USB SETTING, BATTERY CHARGER SET FOR 1A 2.7 3.0 3.3 3.6 3.9 BATTERY VOLTAGE (V) 4.2
4088 G05
0 2.7
3.0
3.6 3.9 3.3 BATTERY VOLTAGE (V)
4.2
4088 G06
Battery Charging Efficiency vs Battery Voltage with No External Load (PBAT/PBUS)
RCLPROG = 2.94k RPROG = 1k IOUT = 0mA 5x CHARGING EFFICIENCY 86 1x CHARGING EFFICIENCY 50
VBUS Current vs VBUS Voltage (Suspend)
IOUT = 0mA
40
30
84
20
82
10
80 2.7
3.0
3.6 3.9 3.3 BATTERY VOLTAGE (V)
4.2
4088 G08
0
1
2
4 3 VBUS VOLTAGE (V)
5
6
4088 G09
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LTC4088 TYPICAL PERFOR A CE CHARACTERISTICS TA = 25C unless otherwise noted.
Output Voltage vs Output Current in Suspend
5.0 5x MODE 4.5 OUTPUT VOLTAGE (V) VBUS CURRENT (mA) 2.0 2.5
5x MODE 1.5
4.0
OUTPUT VOLTAGE (V)
3.5
1x MODE VBUS = 5V VBAT = 3.3V RCLPROG = 2.94k 0 0.5 1.5 2 1 OUTPUT CURRENT (mA) 2.5
4088 G10
3.0
2.5
Battery Charge Current vs Temperature
600 500 CHARGE CURRENT (mA) 400 THERMAL REGULATION 300 200 100 0 -40 -20 4.21
4.19
OUTPUT VOLTAGE (V)
FLOAT VOLTAGE (V)
0
20 40 60 80 TEMPERATURE (C)
Oscillator Frequency vs Temperature
2.35 15
QUIESCENT CURRENT (mA)
12
QUIESCENT CURRENT (mA)
2.30 FREQUENCY (MHz)
2.25
2.20
2.15
2.10 -40
-15
35 10 TEMPERATURE (C)
6
UW
4088 G13
VBUS Current vs Output Current in Suspend
VBUS = 5V VBAT = 3.3V RCLPROG = 2.94k 3.4
3.3V LDO Output Voltage vs Load Current, VBUS = 0V
VBAT = 3.9V, 4.2V 3.2 VBAT = 3.4V VBAT = 3.5V VBAT = 3.6V
3.0
1.0
2.8
0.5 1x MODE 0 0 0.5 1.5 2 1 OUTPUT LOAD CURRENT (mA) 2.5
4088 G11
2.6
VBAT = 3V VBAT = 3.1V VBAT = 3.2V VBAT = 3.3V 0 5 15 20 10 LOAD CURRENT (mA) 25
4088 G12
Battery Charger Float Voltage vs Temperature
3.68
Low-Battery (Instant-On) Output Voltage vs Temperature
VBAT = 2.7V IOUT = 100mA 5x MODE
4.20
3.66
3.64
4.18
3.62
100 120
4.17 -40
-15
35 10 TEMPERATURE (C)
60
85
4088 G14
3.60 -40
-15
35 10 TEMPERATURE (C)
60
85
4088 G15
VBUS Quiescent Current vs Temperature
VBUS = 5V IOUT = 0A 46 5x MODE 44 42 40 38 36 3 -40
Quiescent Current in Suspend vs Temperature
VBUS = 5V IOUT = 0mA SUSP HI
9
1x MODE 6
60
85
4088 G16
-15
35 10 TEMPERATURE (C)
60
85
4088 G17
34 -40
-15
10 35 TEMPERATURE (C)
60
85
4088 G18
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LTC4088 TYPICAL PERFOR A CE CHARACTERISTICS TA = 25C unless otherwise noted.
CHRG Pin Current vs Voltage (Pull-Down State)
100 VBUS = 5V VBAT = 3.8V ILDO3V3 5mA/DIV 0mA VLDO3V3 20mV/DIV AC COUPLED
4088 G20
CHRG PIN CURRENT (mA)
80
60
40
20 VBAT = 3.8V 0 20s/DIV
0
1
3 4 2 CHRG PIN VOLTAGE (V)
PI FU CTIO S
NTC (Pin 1): Input to the NTC Thermistor Monitoring Circuits. The NTC pin connects to a negative temperature coefficient thermistor which is typically co-packaged with the battery pack to determine if the battery is too hot or too cold to charge. If the battery's temperature is out of range, charging is paused until the battery temperature reenters the valid range. A low drift bias resistor is required from VBUS to NTC and a thermistor is required from NTC to ground. If the NTC function is not desired, the NTC pin should be grounded. CLPROG (Pin 2): USB Current Limit Program and Monitor Pin. A 1% resistor from CLPROG to ground determines the upper limit of the current drawn from the VBUS pin. A precise fraction of the input current, hCLPROG, is sent to the CLPROG pin when the high side switch is on. The switching regulator delivers power until the CLPROG pin reaches 1.188V. Therefore, the current drawn from VBUS will be limited to an amount given by hCLPROG and RCLPROG. There are several ratios for hCLPROG available, two of which correspond to the 500mA and 100mA USB specifications. A multilayer ceramic averaging capacitor is also required at CLPROG for filtering. LDO3V3 (Pin 3): LDO Output. The LDO3V3 pin provides a regulated, always-on 3.3V supply voltage. This pin gets its power from VOUT. It may be used for light loads such as a real-time clock or housekeeping microprocessor. A 1F capacitor is required from LDO3V3 to ground if it will be called upon to deliver current. If the LDO3V3 output is not used it should be disabled by connecting it to VOUT. D2 (Pin 4): Mode Select Input Pin. D2, in combination with the D0 pin and D1 pin, controls the current limit and battery charger functions of the LTC4088 (see Table 1). This pin is pulled low by a weak current sink. C/X (Pin 5): End of Charge Indication Program Pin. This pin is used to program the current level at which a completed charge cycle is indicated by the CHRG pin. PROG (Pin 6): Charge Current Program and Charge Current Monitor Pin. Connecting a 1% resistor from PROG to ground programs the charge current. If sufficient input power is available in constant-current mode, this pin servos to 1V. The voltage on this pin always represents the actual charge current by using the following formula: IBAT = VPROG * 1031 RPROG
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4088 G19
3.3V LDO Transient Response (5mA to 15mA)
Suspend LDO Transient Response (500A to 1mA)
IOUT 500A/DIV 0mA VOUT 20mV/DIV AC COUPLED
500s/DIV
4088 G21
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7
LTC4088 PI FU CTIO S
CHRG (Pin 7): Open-Drain Charge Status Output. The CHRG pin indicates the status of the battery charger. Four possible states are represented by CHRG: charging, not charging (or float charge current less than programmed end of charge indication current), unresponsive battery and battery temperature out of range. CHRG is modulated at 35kHz and switches between a low and a high duty cycle for easy recognition by either humans or microprocessors. CHRG requires a pull-up resistor and/or LED to provide indication. GATE (Pin 8): Ideal Diode Amplifier Output. This pin controls the gate of an optional external P-channel MOSFET transistor used to supplement the internal ideal diode. The source of the P-channel MOSFET should be connected to VOUT and the drain should be connected to BAT. BAT (Pin 9): Single Cell Li-Ion Battery Pin. Depending on available power and load, a Li-Ion battery on BAT will either deliver system power to VOUT through the ideal diode or be charged from the battery charger. VOUT (Pin 10): Output voltage of the switching PowerPath controller and input voltage of the battery charger. The majority of the portable product should be powered from VOUT. The LTC4088 will partition the available power between the external load on VOUT and the internal battery charger. Priority is given to the external load and any extra power is used to charge the battery. An ideal diode from BAT to VOUT ensures that VOUT is powered even if the load exceeds the allotted power from VBUS or if the VBUS power source is removed. VOUT should be bypassed with a low impedance multilayer ceramic capacitor. VBUS (Pin 11): Input voltage for the switching PowerPath controller. VBUS will usually be connected to the USB port of a computer or a DC output wall adapter. VBUS should be bypassed with a low impedance multilayer ceramic capacitor. SW (Pin 12): The SW pin delivers power from VBUS to VOUT via the step-down switching regulator. An inductor should be connected from SW to VOUT. See the Applications Information section for a discussion of inductance value and current rating. D0 (Pin 13): Mode Select Input Pin. D0, in combination with the D1 pin and the D2 pin, controls the current limit and battery charger functions of the LTC4088 (see Table 1). This pin is pulled low by a weak current sink. D1 (Pin 14): Mode Select Input Pin. D1, in combination with the D0 pin and the D2 pin, controls the current limit and battery charger functions of the LTC4088 (see Table 1). This pin is pulled low by a weak current sink. Exposed Pad (Pin 15): GND. Must be soldered to the PCB to provide a low electrical and thermal impedance connection to ground.
8
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BLOCK DIAGRA
NONOVERLAP AND DRIVE LOGIC ALWAYS ON 3.3V LDO 3 VOUT LDO3V3 10
TO 3.3V LOAD
ISWITCH/N ILDO/M 100mV
+ - -+
4.6V
2 S Q CONSTANT CURRENT CONSTANT VOLTAGE BATTERY CHARGER R PWM IDEAL DIODE 0V
CLPROG
SUSPEND LDO
OPTIONAL EXTERNAL IDEAL DIODE PMOS
+ - + -
15mV
GATE
8
0.3V 3.6V 1V IBAT/1031
AVERAGE INPUT CURRENT LIMIT CONTROLLER
AVERAGE OUTPUT VOLTAGE LIMIT CONTROLLER
VBUS OSC
UNDERTEMP NTC FAULT LOGIC
IBAT/1031 NTC BAD CELL
T NTC OVERTEMP NTC ENABLE D0 D2 4 13 D1 14
0.1V
+ -
1
NTC
+ -
GND 15
PROG 6 5
C/X
4088 BD
- +
+ -
+ + -
+ -
1.188V
+-
100mV
BAT
9 SINGLE CELL Li-Ion
+
CHRG
7 PWM
W LTC4088
TO USB OR WALL ADPAPTER SW 12
11
VBUS
TO SYSTEM LOAD
+ -
9
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LTC4088 OPERATIO
Introduction The LTC4088 includes a PowerPath controller, battery charger, internal ideal diode, optional external ideal diode controller, SUSPEND LDO and an always-on 3.3V LDO. Designed specifically for USB applications, the PowerPath controller incorporates a precision average input current limited step-down switching regulator to make maximum use of the allowable USB power. Because power is conserved, the LTC4088 allows the load current on VOUT to exceed the current drawn by the USB port without exceeding the USB load specifications. The switching regulator and battery charger communicate to ensure that the average input current never exceeds the USB specifications. The ideal diodes from BAT to VOUT guarantee that ample power is always available to VOUT even if there is insufficient or absent power at VBUS. To prevent battery drain when a device is connected to a suspended USB port, an LDO from VBUS to VOUT provides either low power or high power suspend current to the application. Finally, an "always on" LDO provides a regulated 3.3V from VOUT. This LDO will be on at all times and can be used to supply up to 25mA to a system microprocessor.
TO USB OR WALL ADAPTER
11
VBUS
ISWITCH/N
15mV 0.3V 3.6V
2
1.188V
AVERAGE INPUT CURRENT LIMIT CONTROLLER
AVERAGE OUTPUT VOLTAGE LIMIT CONTROLLER
4088 F01
10
+ + -
+ -
CLPROG
+-
Figure 1
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Input Current Limited Step Down Switching Regulator The power delivered from VBUS to VOUT is controlled by a 2.25MHz constant frequency step-down switching regulator. To meet the USB maximum load specification, the switching regulator contains a measurement and control system that ensures that the average input current remains below the level programmed at CLPROG. VOUT drives the combination of the external load and the battery charger. If the combined load does not cause the switching power supply to reach the programmed input current limit, VOUT will track approximately 0.3V above the battery voltage. By keeping the voltage across the battery charger at this low level, power lost to the battery charger is minimized. Figure 1 shows the power path components. If the combined external load plus battery charge current is large enough to cause the switching power supply to reach the programmed input current limit, the battery charger will reduce its charge current by precisely the amount necessary to enable the external load to be satisfied. Even if the battery charge current is programmed to exceed the allowable USB current, the USB specification for average input current will not be violated; the battery charger will reduce its current as needed. Furthermore, if the load current at VOUT exceeds the programmed power from VBUS,
SW 12 SYSTEM LOAD 3.5V TO (BAT + 0.3V) PWM AND GATE DRIVE IDEAL DIODE CONSTANT CURRENT CONSTANT VOLTAGE BATTERY CHARGER OV VOUT 10
+ -
GATE
8
OPTIONAL EXTERNAL IDEAL DIODE PMOS
BAT
9
+
SINGLE CELL Li-Ion
LTC4088 OPERATIO
load current will be drawn from the battery via the ideal diodes even when the battery charger is enabled. The current at CLPROG is a precise fraction of the VBUS current. When a programming resistor and an averaging capacitor are connected from CLPROG to GND, the voltage on CLPROG represents the average input current of the switching regulator. As the input current approaches the programmed limit, CLPROG reaches 1.188V and power delivered by the switching regulator is held constant. Several ratios of current are available which can be set to correspond to USB low and high power modes with a single programming resistor. The input current limit is programmed by various combinations of the D0, D1 and D2 pins as shown in Table 1. The switching input regulator can also be deactivated (USB Suspend). The average input current will be limited by the CLPROG programming resistor according to the following expression: IVBUS = IBUSQ + VCLPROG * (hCLPROG + 1) RCLPROG
VOUT (V)
where IBUSQ is the quiescent current of the LTC4088, VCLPROG is the CLPROG servo voltage in current limit, RCLPROG is the value of the programming resistor and hCLPROG is the ratio of the measured current at VBUS to the sample current delivered to CLPROG. Refer to the Electrical Characteristics table for values of hCLPROG, VCLPROG and IBUSQ. Given worst-case circuit tolerances, the USB specification for the average input current of 1x or 5x mode will not be violated, provided that RCLPROG is 2.94k or greater. Table 1 shows the available settings for the D0, D1 and D2 pins. Notice that when D0 is high and D1 is low, the switching regulator is set to a higher current limit for increased charging and power availability at VOUT. These modes will typically be used when there is line power available from a wall adapter. While not in current limit, the switching regulator's BatTrack feature will set VOUT to approximately 300mV above
U
Table 1. Controlled Input Current Limit
D0 0 0 0 0 1 1 1 1 D1 0 0 1 1 0 0 1 1 D2 0 1 0 1 0 1 0 1 CHARGER STATUS On Off On Off On Off Off Off IBUS(LIM) 100mA (1x) 100mA (1x) 500mA (5x) 500mA (5x) 1A (10x) 1A (10x) 500A (Susp Low) 2.5mA (Susp High)
the voltage at BAT. However, if the voltage at BAT is below 3.3V, and the load requirement does not cause the switching regulator to exceed its current limit, VOUT will regulate at a fixed 3.6V as shown in Figure 2. This will allow a portable product to run immediately when power is applied without waiting for the battery to charge. If the load does exceed the current limit at VBUS, VOUT will range between the no-load voltage and slighly below the battery voltage, indicated by the shaded region of Figure 2. If there is no battery present when this happens, VOUT may collapse to ground. The voltage regulation loop compensation is controlled by the capacitance on VOUT. An MLCC capacitor of 10F is required for loop stability. Additional capacitance beyond this value will improve transient response.
4.5 4.2 3.9 NO LOAD 3.6 300mV 3.3 3.0 2.7 2.4 2.4
2.7
3.0
3.6 3.3 BAT (V)
3.9
4.2
4088 F02
Figure 2. VOUT vs BAT
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LTC4088 OPERATIO
Ideal Diode from BAT to VOUT The LTC4088 has an internal ideal diode as well as a controller for an optional external ideal diode. Both the internal and the external ideal diodes are always on and will respond quickly whenever VOUT drops below BAT. If the load current increases beyond the power allowed from the switching regulator, additional power will be pulled from the battery via the ideal diodes. Furthermore, if power to VBUS (USB or wall power) is removed, then all of the application power will be provided by the battery via the ideal diodes. The ideal diodes will be fast enough to keep VOUT from drooping with only the storage capacitance required for the switching regulator. The internal ideal diode consists of a precision amplifier that activates a large on-chip MOSFET transistor whenever the voltage at VOUT is approximately 15mV (VFWD) below the voltage at BAT. Within the amplifier's linear range, the small-signal resistance of the ideal diode will be quite low, keeping the forward drop near 15mV. At higher current levels, the MOSFET will be in full conduction. The on-resistance in this case is approximately 180m. If this is sufficient for the application, then no external components are necessary. However, if more conductance is needed, an external P-channel MOSFET transistor can be added from BAT to VOUT. The GATE pin of the LTC4088 drives the gate of the P-channel MOSFET transistor for automatic ideal diode control. The source of the external P-channel MOSFET should be connected to VOUT and the drain should be
2200 2000 1800 1600 CURRENT (mA) 1400 1200 1000 800 600 400 200 0 0 ON SEMICONDUCTOR MBRM120LT3 VBUS = 5V 60 120 180 240 300 360 420 480 FORWARD VOLTAGE (mV) (BAT - VOUT)
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Figure 3. Ideal Diode V-I Characteristics
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connected to BAT. Capable of driving a 1nF load, the GATE pin can control an external P-channel MOSFET transistor having an on-resistance of 30m or lower. When VBUS is unavailable, the forward voltage of the ideal diode amplifier will be reduced from 15mV to nearly zero. Suspend LDO The LTC4088 provides a small amount of power to VOUT in SUSPEND mode by including an LDO from VBUS to VOUT. This LDO will prevent the battery from running down when the portable product has access to a suspended USB port. Regulating at 4.6V, this LDO only becomes active when the switching converter is disabled. To remain compliant with the USB specification, the input to the LDO is current limited so that it will not exceed the low power or high power suspend specification. If the load on VOUT exceeds the suspend current limit, the additional current will come from the battery via the ideal diodes. The suspend LDO sends a scaled copy of the VBUS current to the CLPROG pin, which will servo to approximately 100mV in this mode. Thus, the high power and low power suspend settings are related to the levels programmed by the same resistor for 1x and 5x modes. 3.3V Always-On Supply The LTC4088 includes an ultralow quiescent current low dropout regulator that is always powered. This LDO can be used to provide power to a system pushbutton controller or standby microcontroller. Designed to deliver up to 25mA, the always-on LDO requires a 1F MLCC bypass capacitor for compensation. The LDO is powered from VOUT, and therefore will enter dropout at loads less than 25mA as VOUT falls near 3.3V. If the LDO3V3 output is not used, it should be disabled by connecting it to VOUT. VBUS Undervoltage Lockout (UVLO) An internal undervoltage lockout circuit monitors VBUS and keeps the switching regulator off until VBUS rises above the rising UVLO threshold (4.3V). If VBUS falls below the falling UVLO threshold (4V), system power at VOUT will be drawn from the battery via the ideal diodes. The voltage at VBUS must also be higher than the voltage at BAT by approximately 170mV for the switching regulator to operate.
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VISHAY Si2333 OPTIONAL EXTERNAL IDEAL DIODE
LTC4088 IDEAL DIODE
LTC4088 OPERATIO
Battery Charger The LTC4088 includes a constant-current/constant-voltage battery charger with automatic recharge, automatic termination by safety timer, low voltage trickle charging, bad cell detection and thermistor sensor input for out of temperature charge pausing. When a battery charge cycle begins, the battery charger first determines if the battery is deeply discharged. If the battery voltage is below VTRKL, typically 2.85V, an automatic trickle charge feature sets the battery charge current to 10% of the programmed value. If the low voltage persists for more than 1/2 hour, the battery charger automatically terminates and indicates, via the CHRG pin, that the battery was unresponsive. Once the battery voltage is above VTRKL, the charger begins charging in full power constant-current mode. The current delivered to the battery will try to reach 1031V/RPROG. Depending on available input power and external load conditions, the battery charger may or may not be able to charge at the full programmed rate. The external load will always be prioritized over the battery charge current. The USB current limit programming will always be observed and only additional power will be available to charge the battery. When system loads are light, battery charge current will be maximized. Charge Termination The battery charger has a built-in safety timer. Once the voltage on the battery reaches the pre-programmed float voltage of 4.200V, the charger will regulate the battery voltage there and the charge current will decrease naturally. Once the charger detects that the battery has reached 4.200V, the 4-hour safety timer is started. After the safety timer expires, charging of the battery will discontinue and no more current will be delivered. Automatic Recharge Once the battery charger terminates, it will remain off drawing only microamperes of current from the battery. If the portable product remains in this state long enough, the battery will eventually self discharge. To ensure that the battery is always topped off, a charge cycle will automatically begin when the battery voltage falls below IBAT =
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VRECHRG (typically 4.1V). In the event that the safety timer is running when the battery voltage falls below VRECHRG, it will reset back to zero. To prevent brief excursions below VRECHRG from resetting the safety timer, the battery voltage must be below VRECHRG for more than 1.5ms. The charge cycle and safety timer will also restart if the VBUS UVLO cycles low and then high (e.g., VBUS is removed and then replaced) or if the charger is momentarily disabled using the D2 pin. Charge Current The charge current is programmed using a single resistor from PROG to ground. 1/1031th of the battery charge current is delivered to PROG, which will attempt to servo to 1.000V. Thus, the battery charge current will try to reach 1031 times the current in the PROG pin. The program resistor and the charge current are calculated using the following equations: RPROG = 1031V 1031V , ICHG = ICHG RPROG In either the constant-current or constant-voltage charging modes, the voltage at the PROG pin will be proportional to the actual charge current delivered to the battery. The charge current can be determined at any time by monitoring the PROG pin voltage and using the following equation: VPROG * 1031 RPROG In many cases, the actual battery charge current, IBAT, will be lower than the programmed current, ICHG, due to limited input power available and prioritization to the system load drawn from VOUT. Charge Status Indication The CHRG pin indicates the status of the battery charger. Four possible states are represented by CHRG which include charging, not charging (or float charge current less than programmed end of charge indication current), unresponsive battery and battery temperature out of range. The signal at the CHRG pin can be easily recognized as one of the above four states by either a human or a
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LTC4088 OPERATIO
microprocessor. An open-drain output, the CHRG pin can drive an indicator LED through a current limiting resistor for human interfacing or simply a pull-up resistor for microprocessor interfacing. To make the CHRG pin easily recognized by both humans and microprocessors, the pin is either a DC signal of ON for charging, OFF for not charging or it is switched at high frequency (35kHz) to indicate the two possible faults. While switching at 35kHz, its duty cycle is modulated at a slow rate that can be recognized by a human. When charging begins, CHRG is pulled low and remains low for the duration of a normal charge cycle. When charging is complete, as determined by the criteria set by the C/X pin, the CHRG pin is released (Hi-Z). The CHRG pin does not respond to the C/X threshold if the LTC4088 is in VBUS current limit. This prevents false end of charge indications due to insufficient power available to the battery charger. If a fault occurs while charging, the pin is switched at 35kHz. While switching, its duty cycle is modulated between a high and low value at a very low frequency. The low and high duty cycles are disparate enough to make an LED appear to be on or off thus giving the appearance of "blinking". Each of the two faults has its own unique "blink" rate for human recognition as well as two unique duty cycles for machine recognition. Table 2 illustrates the four possible states of the CHRG pin when the battery charger is active.
Table 2. CHRG Signal
STATUS Charging IBAT < C/X NTC Fault Bad Battery FREQUENCY 0Hz 0Hz 35kHz 35kHz MODULATION (BLINK) FREQUENCY 0Hz (Low Z) 0Hz (Hi-Z) 1.5Hz at 50% 6.1Hz at 50% DUTY CYCLES 100% 0% 6.25% or 93.75% 12.5% or 87.5%
Notice that an NTC fault is represented by a 35kHz pulse train whose duty cycle toggles between 6.25% and 93.75% at a 1.5Hz rate. A human will easily recognize the 1.5Hz rate as a "slow" blinking which indicates the out of range battery temperature while a microprocessor will be able to decode either the 6.25% or 93.75% duty cycles as an NTC fault.
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If a battery is found to be unresponsive to charging (i.e., its voltage remains below 2.85V for 1/2 hour), the CHRG pin gives the battery fault indication. For this fault, a human would easily recognize the frantic 6.1Hz "fast" blink of the LED while a microprocessor would be able to decode either the 12.5% or 87.5% duty cycles as a bad cell fault. Because the LTC4088 is a 3-terminal PowerPath product, system load is always prioritized over battery charging. Due to excessive system load, there may not be sufficient power to charge the battery beyond the bad cell threshold voltage within the bad cell timeout period. In this case the battery charger will falsely indicate a bad cell. System software may then reduce the load and reset the battery charger to try again. Although very improbable, it is possible that a duty cycle reading could be taken at the bright-dim transition (low duty cycle to high duty cycle). When this happens the duty cycle reading will be precisely 50%. If the duty cycle reading is 50%, system software should disqualify it and take a new duty cycle reading. C/X Determination The current exiting the C/X pin represents 1/1031th of the battery charge current. With a resistor from C/X to ground that is X/10 times the resistor at the PROG pin, the CHRG pin releases when the battery current drops to C/X. For example, if C/10 detection is desired, RC/X should be made equal to RPROG. For C/20, RC/X would be twice RPROG. The current threshold at which CHRG will change state is given by: IBAT = VC / X * 1031 RC / X With this design, C/10 detection can be achieved with only one resistor rather than a resistor for both the C/X pin and the PROG pin. Since both of these pins have 1/1031 of the battery charge current in them, their voltages will be equal when they have the same resistor value. Therefore, rather than using two resistors, the C/X pin and the PROG pin can be connected together and the resistors can be paralleled to a single resistor of 1/2 of the program resistor.
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LTC4088 OPERATIO
NTC Thermistor The battery temperature is measured by placing a negative temperature coefficient (NTC) thermistor close to the battery pack. The NTC circuitry is shown in the Block Diagram. To use this feature, connect the NTC thermistor, RNTC, between the NTC pin and ground and a bias resistor, RNOM, from VBUS to NTC. RNOM should be a 1% resistor with a value equal to the value of the chosen NTC thermistor at 25C (R25). A 100k thermistor is recommended since thermistor current is not measured by the LTC4088 and will have to be considered for USB compliance. The LTC4088 will pause charging when the resistance of the NTC thermistor drops to 0.54 times the value of R25 or approximately 54k (for a Vishay "Curve 1" thermistor, this corresponds to approximately 40C). If the battery charger is in constant voltage (float) mode, the safety timer also pauses until the thermistor indicates a return to a valid temperature. As the temperature drops, the resistance of the NTC thermistor rises. The LTC4088 is also designed to pause charging when the value of the NTC thermistor increases to 3.25 times the value of R25. For a Vishay "Curve 1" thermistor, this resistance, 325k, corresponds to approximately 0C. The hot and cold comparators each have approximately 3C of hysteresis to prevent oscillation about the trip point. Grounding the NTC pin disables all NTC functionality.
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Thermal Regulation To prevent thermal damage to the IC or surrounding components, an internal thermal feedback loop will automatically decrease the programmed charge current if the die temperature rises to approximately 110C. Thermal regulation protects the LTC4088 from excessive temperature due to high power operation or high ambient thermal conditions, and allows the user to push the limits of the power handling capability with a given circuit board design without risk of damaging the LTC4088 or external components. The benefit of the LTC4088 thermal regulation loop is that charge current can be set according to actual conditions rather than worst-case conditions for a given application with the assurance that the charger will automatically reduce the current in worst-case conditions. Shutdown Mode For autonomous battery charger operation, D2 should be permanently grounded. However, for more control via software the LTC4088's battery charger can be independently disabled by bringing the D2 pin above VIH. D2 must also be brought high to enable high power (2.5mA) suspend mode. The input switching regulator is enabled whenever VBUS is above the UVLO voltage and the LTC4088 is not in one of the two USB suspend modes (500A or 2.5mA). The ideal diode is enabled at all times and cannot be disabled.
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LTC4088 APPLICATIO S I FOR ATIO
CLPROG Resistor and Capacitor As described in the Step-Down Input Regulator section, the resistor on the CLPROG pin determines the average input current limit in each of the six current limit modes. The input current will be comprised of two components, the current that is used to drive VOUT and the quiescent current of the switching regulator. To ensure that the USB specification is strictly met, both components of input current should be considered. The Electrical Characteristics table gives the typical values for quiescent currents in all settings as well as current limit programming accuracy. To get as close to the 500mA or 100mA specifications as possible, a precision resistor should be used. An averaging capacitor is required in parallel with the resistor so that the switching regulator can determine the average input current. This capacitor also provides the dominant pole for the feedback loop when current limit is reached. To ensure stability, the capacitor on CLPROG should be 0.47F or larger. Alternatively, faster transient response may be achieved with 0.1F in series with 8.2. Choosing the Inductor Because the average input current circuit does not measure reverse current (i.e., current from VOUT to VBUS), current reversal in the inductor at light loads will contribute an error to the VBUS current measurement. The error is conservative in that if the current reverses, the voltage at CLPROG will be higher than what would represent the actual average input current drawn. The current available for charging and the system load is thus reduced. The USB specification will not be violated. This reduction in available VBUS current will happen when the peak-peak inductor ripple is greater than twice the average current limit setting. For example, if the average current limit is set to 100mA, the peak-peak ripple should not exceed 200mA. If the input current is less than 100mA, the measurement accuracy may be reduced, but it does not affect the average current loop since it will not be in regulation. The LTC4088 includes a current-reversal comparator which monitors inductor current and disables the synchronous
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rectifier as current approaches zero. This comparator will minimize the effect of current reversal on the average input current measurement. For some low inductance values, however, the inductor current may reverse slightly. This value depends on the speed of the comparator in relation to the slope of the current waveform, given by VL/L, where VL is the voltage across the inductor (approximately -VOUT) and L is the inductance value. An inductance value of 3.3H is a good starting value. The ripple will be small enough for the regulator to remain in continuous conduction at 100mA average VBUS current. At lighter loads the current-reversal comparator will disable the synchronous rectifier at a current slightly above 0mA. As the inductance is reduced from this value, the part will enter discontinuous conduction mode at progressively higher loads. Ripple at VOUT will increase, directly proportionally to the magnitude of inductor ripple. Transient response, however, will be improved. The current mode controller controls inductor current to exactly the amount required by the load to keep VOUT in regulation. A transient load step requires the inductor current to change to a new level. Since inductor current cannot change instantaneously, the capacitance on VOUT delivers or absorbs the difference in current until the inductor current can change to meet the new load demand. A smaller inductor changes its current more quickly for a given voltage drive than a larger inductor, resulting in faster transient response. A larger inductor will reduce output ripple and current ripple, but at the expense of reduced transient performance (or more CVOUT required) and a physically larger inductor package size. The input regulator has an instantaneous peak current clamp to prevent the inductor from saturating during transient load or start-up conditions. The clamp is designed so that it does not interfere with normal operation at high loads with reasonable inductor ripple. It will prevent inductor current runaway in case of a shorted output. The DC winding resistance and AC core losses of the inductor will affect efficiency, and therefore available output power. These effects are difficult to characterize and vary by application. Some inductors which may be suitable for this application are listed in Table 3.
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LTC4088 APPLICATIO S I FOR ATIO
INDUCTOR TYPE LPS4018 D53LC DB318C WE-TPC Type M1 CDRH6D12 CDRH6D38 L (H) 3.3 3.3 3.3 3.3 3.3 3.3
Table 3. Recommended Inductors for the LTC4088
MAX IDC MAX DCR (A) () 2.2 2.26 1.55 1.95 2.2 3.5 0.08 0.034 0.070 0.065 0.0625 0.020 SIZE IN mm (L x W x H) 3.9 x 3.9 x 1.7 5x5x3 3.8 x 3.8 x 1.8 4.8 x 4.8 x 1.8 6.7 x 6.7 x 1.5 7x7x4 MANUFACTURER Coilcraft www.coilcraft.com Toko www.toko.com Wurth Elektronik www.we-online.com Sumida www.sumida.com
VBUS and VOUT Bypass Capacitors The style and value of capacitors used with the LTC4088 determine several important parameters such as regulator control-loop stability and input voltage ripple. Because the LTC4088 uses a step-down switching power supply from VBUS to VOUT, its input current waveform contains high frequency components. It is strongly recommended that a low equivalent series resistance (ESR) multilayer ceramic capacitor be used to bypass VBUS. Tantalum and aluminum capacitors are not recommended because of their high ESR. The value of the capacitor on VBUS directly controls the amount of input ripple for a given load current. Increasing the size of this capacitor will reduce the input ripple. The USB specification allows a maximum of 10F to be connected directly across the USB power bus. If additional capacitance is required for noise performance, a soft-connect circuit may be required to limit inrush current and avoid excessive transient voltage drops on the bus (see Figure 5). To prevent large VOUT voltage steps during transient load conditions, it is also recommended that a ceramic capacitor be used to bypass VOUT. The output capacitor is used in the compensation of the switching regulator. At least 10F with low ESR are required on VOUT. Additional capacitance will improve load transient performance and stability. Multilayer ceramic chip capacitors typically have exceptional ESR performance. MLCCs combined with a tight board layout and an unbroken ground plane will yield very good performance and low EMI emissions. There are several types of ceramic capacitors available each having considerably different characteristics.
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For example, X7R ceramic capacitors have the best voltage and temperature stability. X5R ceramic capacitors have apparently higher packing density but poorer performance over their rated voltage and temperature ranges. Y5V ceramic capacitors have the highest packing density, but must be used with caution, because of their extreme nonlinear characteristic of capacitance versus voltage. The actual in-circuit capacitance of a ceramic capacitor should be measured with a small AC signal and DC bias as is expected in-circuit. Many vendors specify the capacitance verse voltage with a 1VRMS AC test signal and, as a result, over state the capacitance that the capacitor will present in the application. Using similar operating conditions as the application, the user must measure or request from the vendor the actual capacitance to determine if the selected capacitor meets the minimum capacitance that the application requires. Overprogramming the Battery Charger The USB high power specification allows for up to 2.5W to be drawn from the USB port. The switching regulator transforms the voltage at VBUS to just above the voltage at BAT with high efficiency, while limiting power to less than the amount programmed at CLPROG. The charger should be programmed (with the PROG pin) to deliver the maximum safe charging current without regard to the USB specifications. If there is insufficient current available to charge the battery at the programmed rate, it will reduce charge current until the system load on VOUT is satisfied and the VBUS current limit is satisfied. Programming the charger for more current than is available will not cause the average input current limit to be violated. It will merely allow the battery charger to make use of all available
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LTC4088 APPLICATIO S I FOR ATIO
power to charge the battery as quickly as possible, and with minimal power dissipation within the charger. Alternate NTC Thermistors and Biasing The LTC4088 provides temperature qualified charging if a grounded thermistor and a bias resistor are connected to NTC. By using a bias resistor whose value is equal to the room temperature resistance of the thermistor (R25) the upper and lower temperatures are pre-programmed to approximately 40C and 0C, respectively (assuming a Vishay "Curve 1" thermistor). The upper and lower temperature thresholds can be adjusted by either a modification of the bias resistor value or by adding a second adjustment resistor to the circuit. If only the bias resistor is adjusted, then either the upper or the lower threshold can be modified but not both. The other trip point will be determined by the characteristics of the thermistor. Using the bias resistor in addition to an adjustment resistor, both the upper and the lower temperature trip points can be independently programmed with the constraint that the difference between the upper and lower temperature thresholds cannot decrease. Examples of each technique are given below. NTC thermistors have temperature characteristics which are indicated on resistance-temperature conversion tables. The Vishay-Dale thermistor NTHS0603N011-N1003F, used in the following examples, has a nominal value of 100k and follows the Vishay "Curve 1" resistance-temperature characteristic. In the explanation below, the following notation is used. R25 = Value of the Thermistor at 25C RNTC|COLD = Value of thermistor at the cold trip point RNTC|HOT = Value of the thermistor at the hot trip point rCOLD = Ratio of RNTC|COLD to R25 rHOT = Ratio of RNTC|COLD to R25 RNOM = Primary thermistor bias resistor (see Figure 2) R1 = Optional temperature range adjustment resistor (see Figure 3) RNOM = RNOM =
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The trip points for the LTC4088's temperature qualification are internally programmed at 0.349 * VBUS for the hot threshold and 0.765 * VBUS for the cold threshold. Therefore, the hot trip point is set when: RNTCHOT | RNOM + RNTCHOT | * VBUS = 0.349 * VBUS and the cold trip point is set when: RNTC|COLD RNOM + RNTC|COLD * VBUS = 0.765 * VBUS Solving these equations for RNTC|COLD and RNTC|HOT results in the following: RNTC|HOT = 0.536 * RNOM and RNTC|COLD = 3.25 * RNOM By setting RNOM equal to R25, the above equations result in rHOT = 0.536 and rCOLD = 3.25. Referencing these ratios to the Vishay Resistance-Temperature Curve 1 chart gives a hot trip point of about 40C and a cold trip point of about 0C. The difference between the hot and cold trip points is approximately 40C. By using a bias resistor, RNOM, different in value from R25, the hot and cold trip points can be moved in either direction. The temperature span will change somewhat due to the non-linear behavior of the thermistor. The following equations can be used to easily calculate a new value for the bias resistor: rHOT * R25 0.536 rCOLD * R25 3.25 where rHOT and rCOLD are the resistance ratios at the desired hot and cold trip points. Note that these equations are linked. Therefore, only one of the two trip points can be chosen, the other is determined by the default ratios designed in the IC. Consider an example where a 60C hot trip point is desired.
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LTC4088 APPLICATIO S I FOR ATIO
From the Vishay Curve 1 R-T characteristics, rHOT is 0.2488 at 60C. Using the above equation, RNOM should be set to 46.4k. With this value of RNOM, the cold trip point is about 16C. Notice that the span is now 44C rather than the previous 40C. This is due to the decrease in "temperature gain" of the thermistor as absolute temperature increases. The upper and lower temperature trip points can be independently programmed by using an additional bias resistor as shown in Figure 4b. The following formulas can be used to compute the values of RNOM and R1: r -r RNOM = COLD HOT * R25 2.714 R1 = 0.536 * RNOM - rHOT * R25 For example, to set the trip points to 0C and 45C with a Vishay Curve 1 thermistor choose:
5V USB INPUT
3.266 - 0.4368 RNOM = * 100k = 104.2k 2.714 the nearest 1% value is 105k: R1 = 0.536 * 105k - 0.4368 * 100k = 12.6k
LTC4088 NTC BLOCK VBUS
VBUS
VBUS
RNOM 100k NTC 1 RNTC 100k
0.765 * VBUS
-
TOO_COLD
+
T
-
TOO_HOT 0.349 * VBUS
+
+
NTC_ENABLE 0.1V
-
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(4a) Figure 4. NTC Circuits
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the nearest 1% value is 12.7k. The final solution is shown in Figure 4b and results in an upper trip point of 45C and a lower trip point of 0C. USB Inrush Limiting The USB specification allows at most 10F of downstream capacitance to be hot-plugged into a USB hub. In most LTC4088 applications, 10F should be enough to provide adequate filtering on VBUS. If more capacitance is required, the following circuit can be used to soft-connect additional capacitance. In this circuit, capacitor C1 holds MP1 off when the cable is first connected. Eventually the bottom plate of C1 discharges to GND, applying increasing gate support to MP1.
MP1 Si2333 VBUS C1 100nF USB CABLE R1 40k GND
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C2
LTC4088
Figure 5. USB Soft-Connect Circuit
VBUS
LTC4088 NTC BLOCK
RNOM 105k NTC 1
0.765 * VBUS
-
TOO_COLD
+
R1 12.7k 0.349 * VBUS T RNTC 100k
-
TOO_HOT
+
+
NTC_ENABLE 0.1V
-
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(4b)
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LTC4088 APPLICATIO S I FOR ATIO
The long time constant of R1 and C1 prevent the current from building up in the cable too fast, thus dampening out any resonant overshoot. Voltage overshoot on VBUS may sometimes be observed when connecting the LTC4088 to a lab power supply. This overshoot is caused by long leads from the power supply to VBUS. Twisting the wires together from the supply to VBUS can greatly reduce the parasitic inductance of these long leads, and keep the voltage at VBUS to safe levels. USB cables are generally manufactured with the power leads in close proximity, and thus fairly low parasitic inductance. Board Layout Considerations The Exposed Pad on the backside of the LTC4088 package must be securely soldered to the PC board ground. This is the only ground pin in the package, and it serves as the return path for both the control circuitry and the synchronous rectifier. Furthermore, due to its high frequency switching circuitry, it is imperative that the input capacitor, inductor, and output capacitor be as close to the LTC4088 as possible and that there be an unbroken ground plane under the LTC4088
Figure 6. Ground Currents Follow Their Incident Path at High Speed. Slices in the Ground Plane Cause High Voltage and Increased Emissions
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and all of its external high frequency components. High frequency currents, such as the input current on the LTC4088, tend to find their way on the ground plane along a mirror path directly beneath the incident path on the top of the board. If there are slits or cuts in the ground plane due to other traces on that layer, the current will be forced to go around the slits. If high frequency currents are not allowed to flow back through their natural least-area path, excessive voltage will build up and radiated emissions will occur (see Figure 6). There should be a group of vias directly under the grounded backside leading directly down to an internal ground plane. To minimize parasitic inductance, the ground plane should be as close as possible to the top plane of the PC board (layer 2). The GATE pin for the external ideal diode controller has extremely limited drive current. Care must be taken to minimize leakage to adjacent PC board traces. 100nA of leakage from this pin will introduce an additional offset to the ideal diode of approximately 10mV. To minimize leakage, the trace can be guarded on the PC board by surrounding it with VOUT connected metal, which should generally be less than one volt higher than GATE.
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LTC4088 APPLICATIO S I FOR ATIO
Battery Charger Stability Considerations The LTC4088's battery charger contains both a constant-voltage and a constant-current control loop. The constant-voltage loop is stable without any compensation when a battery is connected with low impedance leads. Excessive lead length, however, may add enough series inductance to require a bypass capacitor of at least 1F from BAT to GND. High value, low ESR multilayer ceramic chip capacitors reduce the constant-voltage loop phase margin, possibly resulting in instability. Ceramic capacitors up to 22F may be used in parallel with a battery, but larger ceramics should be decoupled with 0.2 to 1 of series resistance. Furthermore, a 4.7F capacitor in series with a 0.2 to 1 resistor from BAT to GND is required to prevent oscillation when the battery is disconnected.
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In constant-current mode, the PROG pin is in the feedback loop rather than the battery voltage. Because of the additional pole created by any PROG pin capacitance, capacitance on this pin must be kept to a minimum. With no additional capacitance on the PROG pin, the charger is stable with program resistor values as high as 25k. However, additional capacitance on this node reduces the maximum allowed program resistor. The pole frequency at the PROG pin should be kept above 100kHz. Therefore, if the PROG pin has a parasitic capacitance, CPROG, the following equation should be used to calculate the maximum resistance value for RPROG: RPROG 1 2 * 100kHz * CPROG
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LTC4088 TYPICAL APPLICATIO S
High Efficiency Battery Charger/USB Power Manager with NTC Qualified Charging and Reverse Input Protection
WALL M2 L1 3.3H
USB
WALL
USB
C1 10F 0805
C1, C3: MURATA GRM21BR61A106KE19 C2: MURATA GRM188R71C104KA01 L1: COILCRAFT LPS4018-332MLC R2: VISHAY-DALE NTHS0603N011-N1003F
CHARGE CURRENT (mA)
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VBUS R1 100k C1 10F 0805 D0 D1 D2 CHRG NTC CLPROG R2 T 100k R5 8.2
SW
VOUT
LOAD
LDO3V3 LTC4088 GATE BAT PROG C/X GND R4 499
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C
M1 C3 10F 0805
+
Li-Ion
C2 0.1F 0603
R3 2.94k
C1, C3: MURATA GRM21BR61A106KE19 C2: MURATA GRM188R71C104KA01 L1: COILCRAFT LPS4018-332MLC M1, M2: SILICONIX Si2333 R2: VISHAY-DALE NTHS0603N011-N1003F
USB Compliant Switching Charger
L1 3.3H
VBUS R1 100k D0 D1 D2 CHRG NTC CLPROG R2 T 100k R5 8.2
SW
VOUT C3 10F 0805 LOAD
LDO3V3 LTC4088 GATE BAT PROG C/X GND R4 499
4088 TA03a
C
+
Li-Ion
C2 0.1F 0603
R3 2.94k
700 IBAT 600 500 IBUS 400 300 200 100 5x USB SETTING, BATTERY CHARGER SET FOR 1A 0 3.0 3.3 3.6 2.7 3.9 BATTERY VOLTAGE (V)
4.2
4088 TA03b
4088f
LTC4088 PACKAGE DESCRIPTIO U
DE Package 14-Lead Plastic DFN (4mm x 3mm)
(Reference LTC DWG # 05-08-1708 Rev B)
0.70 0.05 3.60 0.05 2.20 0.05 3.30 0.05 1.70 0.05 PACKAGE OUTLINE 0.25 0.05 0.50 BSC 3.00 REF RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED R = 0.115 TYP R = 0.05 TYP 8 14 0.40 0.10 3.00 0.10 (2 SIDES) PIN 1 TOP MARK (SEE NOTE 6) 7 0.200 REF 0.75 0.05 3.00 REF 0.00 - 0.05 BOTTOM VIEW--EXPOSED PAD 3.30 0.10 1.70 0.10 PIN 1 NOTCH R = 0.20 OR 0.35 x 45 CHAMFER
(DE14) DFN 0806 REV B
4.00 0.10 (2 SIDES)
1 0.25 0.05 0.50 BSC
NOTE: 1. DRAWING PROPOSED TO BE MADE VARIATION OF VERSION (WGED-3) IN JEDEC PACKAGE OUTLINE MO-229 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE
4088f
Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
23
LTC4088 RELATED PARTS
PART NUMBER Battery Chargers LTC4057 LTC4058 LTC4065/LTC4065A LTC4411/LTC4412 LTC4413 Power Management LTC3406/LTC3406A LTC3411 LTC3455 LTC4055 LTC4066 LTC4085 600mA (IOUT), 1.5MHz, Synchronous Step-Down DC/DC Converter 1.25A (IOUT), 4MHz, Synchronous Step-Down DC/DC Converter 95% Efficiency, VIN = 2.5V to 5.5V, VOUT = 0.6V, IQ = 20A, ISD < 1A, ThinSOT Package 95% Efficiency, VIN = 2.5V to 5.5V, VOUT = 0.8V, IQ = 60A, ISD < 1A, MS10 Package Lithium-Ion Linear Battery Charger Standalone 950mA Lithium-Ion Charger in DFN 750mA Linear Lithium-Ion Battery Charger Low Loss Single PowerPath Controllers in ThinSOT Dual Ideal Diodes Up to 800mA Charge Current, Thermal Regulation, ThinSOTTM Package C/10 Charge Termination, Battery Kelvin Sensing, 7% Charge Accuracy 2mm x 2mm DFN Package, Thermal Regulation, Standalone Operation Automatic Switching Between DC Sources, Load Sharing, Replaces ORing Diodes 3mm x 3mm DFN Package, Low Loss Replacement for ORing Diodes DESCRIPTION COMMENTS
Dual DC/DC Converter with USB Power Manager Seamless Transition Between Power Sources: USB, Wall Adapter and and Li-Ion Battery Charger Battery; 95% Efficient DC/DC Conversion USB Power Controller and Battery Charger USB Power Controller and Battery Charger USB Power Manager with Ideal Diode Controller and Li-Ion Charger High Efficiency USB Power Manager and Battery Charger with Regulated Output Voltage Charges Single Cell Li-Ion Batteries Directly from a USB Port, Thermal Regulation, 200m Ideal Diode, 4mm x 4mm QFN16 Package Charges Single Cell Li-Ion Batteries Directly from a USB Port, Thermal Regulation, 50m Ideal Diode, 4mm x 4mm QFN24 Package Charges Single Cell Li-Ion Batteries Directly from a USB Port, Thermal Regulation, 200m Ideal Diode with <50m Option, 4mm x 3mm DFN14 Package Maximizes Available Power from USB Port, Bat-Track, "Instant-On" Operation, 1.5A Max Charge Current, 180m Ideal Diode with <50m Option, Automatic Charge Current Reduction Maintains 3.6V Minimum VOUT, 4mm x 3mm DFN14 Package High Efficiency 1.2A Charger from 6V to 36V (40V Max) Input. Charges Single Cell Li-Ion/Polymer Batteries Directly from a USB Port, Thermal Regulation, 200m Ideal Diode with <50m Option, 4mm x 3mm DFN14 Package. Bat-Track Adaptive Output Control (LTC4089), Fixed 5V Output (LTC4089-5)
LTC4088-1
LTC4089/LTC4089-5
USB Power Manager with Ideal Diode Controller and High Efficiency Li-Ion Battery Charger
ThinSOT is a trademark of Linear Technology Corporation.
4088f
24 Linear Technology Corporation
(408) 432-1900
LT 0307 * PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
FAX: (408) 434-0507 www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2007

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