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FEATURES
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LT3495/LT3495B/ LT3495-1/LT3495B-1 650mA/350mA Micropower Low Noise Boost Converter with Output Disconnect DESCRIPTION
The LT(R)3495/LT3495B/LT3495-1/LT3495B-1 are low noise boost converters with integrated power switch, feedback resistor and output disconnect circuitry. The parts control power delivery by varying both the peak inductor current and switch off-time. This novel* control scheme results in low output voltage ripple as well as high efficiency over a wide load range. For the LT3495/LT3495-1, the off-time of the switch is not allowed to exceed a fixed level, guaranteeing the switching frequency stays above the audio band for the entire load range. The parts feature a high performance NPN power switch with a 650mA and 350mA current limit for the LT3495/LT3495B and LT3495-1/LT3495B-1 respectively. The quiescent current is a low 60A, which is further reduced to 0.1A in shutdown. The internal disconnect circuitry allows the output voltage to be isolated from the input during shutdown. An auxiliary reference input (CTRL pin) overrides the internal 1.235V feedback reference with any lower value allowing full control of the output voltage during operation. The LT3495 series are available in a tiny 10-lead 3mm x 2mm DFN package.
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Low Quiescent Current 60A in Active Mode 0.1A in Shutdown Mode Low Noise Control Scheme (Switching Frequency Always Stays Above Audible Range for LT3495/-1) Integrated Power NPN: 650mA Current Limit (LT3495/B) 350mA Current Limit (LT3495-1/B-1) Integrated Output Disconnect Integrated Output Dimming Wide input range: 2.3V to 16V Wide output range : Up to 40V Integrated feedback resistor Tiny 10-Lead 3mm x 2mm DFN Package
APPLICATIONS
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OLED Power Low Noise Power MP3 Player
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. *Patent pending.
TYPICAL APPLICATION
OLED Power Supply from One Li-Ion Cell
VOUT PEAK-TO-PEAK RIPPLE (mV) ONE Li-Ion CELL 10H 4.7F SW VCC SHDN CTRL CAP VOUT 909k FB GND
3495 TA01a
Output Voltage Ripple vs Load Current
50 1.0F 0603 CAPACITOR AT VOUT EFFICIENCY (%) 90
Efficiency vs Load Current
VIN = 3.6V 400 LOAD FROM CAP LOAD FROM VOUT 320 POWER LOSS (mW)
2.2F VOUT 16V 70mA 1F
40
80
LT3495
30
70
240
20
60
160
10
2.2F 1206 CAPACITOR AT VOUT 0 1 10 LOAD CURRENT (mA) 100
3495 TA01b
50
80
0
40 0.1
1 10 LOAD CURRENT (mA)
0 100
3495 TA01c
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LT3495/LT3495B/ LT3495-1/LT3495B-1 ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW GND 1 GND 2 VCC 3 CTRL 4 SHDN 5 11 10 SW 9 8 7 6 CAP CAP VOUT FB
VCC Voltage ...............................................................16V SW Voltage ...............................................................40V CAP Voltage ..............................................................40V VOUT Voltage .............................................................40V SHDN Voltage ...........................................................10V CTRL Voltage ............................................................10V FB Voltage ................................................................2.5V Maximum Junction Temperature........................... 125C Operating Temperature Range (Note 2).. -40C to 125C Storage Temperature Range................... -65C to 150C
DDB PACKAGE 10-LEAD (3mm x 2mm) PLASTIC DFN TJMAX = 125C, JA = 76C/W EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH LT3495EDDB#PBF LT3495EDDB-1#PBF LT3495BEDDB#PBF LT3495BEDDB-1#PBF TAPE AND REEL LT3495EDDB#TRPBF LT3495EDDB-1#TRPBF LT3495BEDDB#TRPBF LT3495BEDDB-1#TRPBF PART MARKING LDSS LDSV LDST LDSW PACKAGE DESCRIPTION 10-Lead (3mm x 2mm) Plastic DFN 10-Lead (3mm x 2mm) Plastic DFN 10-Lead (3mm x 2mm) Plastic DFN 10-Lead (3mm x 2mm) Plastic DFN TEMPERATURE RANGE -40C to 125C -40C to 125C -40C to 125C -40C to 125C
Consult LTC Marketing for parts specified with wider operating temperature ranges. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
ELECTRICAL CHARACTERISTICS
PARAMETER Minimum Operating Voltage Maximum Operating Voltage FB Voltage FB Voltage Line Regulation FB Resistor Quiescent Current Quiescent Current in Shutdown Minimum Switch-Off Time Maximum Switch-Off Time Maximum Switch-On Time Switch Current Limit
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 3V, VSHDN = VCC, unless otherwise noted. (Note 2)
CONDITIONS MIN TYP 2.2 VCTRL = 3V, (Note 3) FB Voltage = 1.235V Not Switching VSHDN = 0V, VCC = 3V After Start-Up (Note 4) During Start-Up (Note 4) LT3495/LT3495-1, VFB = 1.5V LT3495/LT3495B
l l l l
MAX 2.5 16 1.255 77 70 1
UNITS V V V %/V k A A ns ns
1.220 74.7
1.235 0.03 76 60 0 200 500
17 550
26 10 650
35 780
s s mA
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LT3495/LT3495B/ LT3495-1/LT3495B-1 ELECTRICAL CHARACTERISTICS
PARAMETER Switch Current Limit Switch VCESAT Switch Leakage Current PMOS Disconnect Current Limit PMOS Disconnect VCAP - VOUT VCAP - VOUT Clamp Voltage SHDN Input Voltage High SHDN Input Voltage Low SHDN Pin Bias Current CTRL Pin Bias Current CTRL to FB Offset Maximum Shunt Current VSHDN = 3V VSHDN = 0V VCTRL = 0.5V, Current Flows Out of Pin VCTRL = 0.5V LT3495/LT3495-1, VFB = 1.5V
l
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 3V, VSHDN = VCC, unless otherwise noted. (Note 2)
CONDITIONS LT3495-1/LT3495B-1 LT3495/LT3495B, ISW = 400mA LT3495-1/LT3495B-1, ISW = 200mA VSW = 5V After Start-Up During Start-Up IOUT = 50mA, VCAP = 15V 1.5 0.3 5.3 0 20 6 230 8 100 14 250 110
l
MIN 275
TYP 350 200 125 0.01 370 150 150 8.7
MAX 450
UNITS mA mV mV
1 450 190
A mA mA mV V V V A A nA mV A
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 LT3495/LT3495B/LT3495-1/LT3495B-1 are guaranteed to meet performance specifications from 0C to 125C junction temperature. Specifications over the -40C to 125C operating junction temperature range are assured by design, characterization and correlation with statistical process controls.
Note 3: Internal reference voltage is determined by finding VFB voltage level which causes quiescent current to increase 150A above "Not Switching" level. Note 4: If CTRL is overriding the internal reference, Start-Up mode occurs when VFB is less then half the voltage on CTRL. If CTRL is not overriding the internal reference, Start-Up mode occurs when VFB is less then half the voltage of the internal reference.
TYPICAL PERFORMANCE CHARACTERISTICS
Switching Frequency vs Load Current
1000 VCC = 3.6V VOUT = 16V FIGURE 7 CIRCUIT VOUT VOLTAGE CHANGE (%) 1.5
TA = 25C unless otherwise noted.
Load Regulation
VCC = 3.6V VOUT = 16V 1.0 FIGURE 7 CIRCUIT 0.5 0.0 -0.5 -1.0 -1.5 VOUT VOLTAGE (V) 0 20 40 80 60 LOAD CURRENT (mA) 100 120
3495 G02
VOUT vs CTRL Voltage
18 15 12 9 6 3 0 FIGURE 7 CIRCUIT
SWITCHING FREQUENCY (kHz)
800
600
400
200
0
0
20
40 80 60 LOAD CURRENT (mA)
100
120
3495 G01
0
0.3
0.6 0.9 CTRL VOLTAGE (V)
1.2
1.5
3495 G03
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LT3495/LT3495B/ LT3495-1/LT3495B-1 TYPICAL PERFORMANCE CHARACTERISTICS
Output Voltage vs Temperature
1.00 MINIMUM SWITCHING FREQUENCY (kHz) OUTPUT VOLTAGE CHANGE (%) VCC = 3.6V 0.75 VOUT = 16V LOAD = 5mA 0.50 FIGURE 7 CIRCUIT 0.25 0.00 -0.25 -0.50 -0.75 -1.00 -40 0 40 80 TEMPERATURE (C) 125
3495 G04
TA = 25C unless otherwise noted.
Minimum Switching Frequency
50 FIGURE 7 CIRCUIT QUIESCENT CURRENT (A) 40 80 TEMPERATURE (C) 125
3495 G05
Quiescent Current - Not Switching
100
45
90
80
40
70
35
60
30 -40
0
50
2
4
6
8 10 VCC (V)
12
14
16
3495 G06
Quiescent Current vs Temperature
100 300 250 SWITCH VCESAT (mV) 200 150 100 50 0
SW Saturation Voltage vs Switch Current (LT3495)
200
SW Saturation Voltage vs Switch Current (LT3495-1)
QUIESCENT CURRENT (A)
90
160 SWITCH VCESAT (mV) 0 200 300 400 500 SWITCH CURRENT (mA) 700
80
120
70
80
60
40
50 -40
0
40 80 TEMPERATURE (C)
125
3495 G07
100
600
0
0
100 200 300 SWITCH CURRENT (mA)
400
3495 G09
3495 G08
SHDN Current vs SHDN Voltage
20 1000 INDUCTOR PEAK CURRENT (mA)
Peak Inductor Current vs Temperature (LT3495)
VCC = 3.6V VOUT = 16V FIGURE 7 CIRCUIT 600 INDUCTOR PEAK CURRENT (mA) 550 500 450 400 350
Peak Inductor Current vs Temperature (LT3495-1)
FIGURE 9 CIRCUIT
SHDN PIN CURRENT (A)
15
900
10
800
5
700
0
0
2
4 6 8 SHDN PIN VOLTAGE (V)
10
3495 G10
600 -40
0
40 80 TEMPERATURE (C)
125
3495 G11
300 -40
0
40 80 TEMPERATURE (C)
125
3495 G12
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LT3495/LT3495B/ LT3495-1/LT3495B-1 TYPICAL PERFORMANCE CHARACTERISTICS
LT3495 Switching Waveform at No Load
VOUT VOLTAGE 10mV/DIV AC COUPLED VOUT VOLTAGE 50mV/DIV AC COUPLED
TA = 25C unless otherwise noted. LT3495 Switching Waveform at 10mA
SW VOLTAGE 10V/DIV
SW VOLTAGE 10V/DIV
INDUCTOR CURRENT 100mA/DIV 10s/DIV
3495 G13
INDUCTOR CURRENT 500mA/DIV 2s/DIV
3495 G14
VCC = 3.6V VOUT = 16V
VCC = 3.6V VOUT = 16V
LT3495 Switching Waveform at 80mA
VOUT VOLTAGE 50mV/DIV AC COUPLED VOUT VOLTAGE 20mV/DIV AC COUPLED
LT3495B-1 Switching Waveform at No Load
SW VOLTAGE 10V/DIV
SW VOLTAGE 10V/DIV
INDUCTOR CURRENT 500mA/DIV 500ns/DIV
3495 G15
INDUCTOR CURRENT 100mA/DIV 20s/DIV
3495 G16
VCC = 3.6V VOUT = 16V
VCC = 5V VOUT = 16V
LT3495B-1 Switching Waveform at 10mA
VOUT VOLTAGE 50mV/DIV AC COUPLED VOUT VOLTAGE 50mV/DIV AC COUPLED
LT3495B-1 Switching Waveform at 60mA
SW VOLTAGE 10V/DIV
SW VOLTAGE 10V/DIV
INDUCTOR CURRENT 200mA/DIV 2s/DIV
3495 G17
INDUCTOR CURRENT 200mA/DIV 500ns/DIV
3495 G18
VCC = 5V VOUT = 16V
VCC = 5V VOUT = 16V
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LT3495/LT3495B/ LT3495-1/LT3495B-1 TYPICAL PERFORMANCE CHARACTERISTICS
Line Regulation
0.30 OUTPUT VOLTAGE CHANGE (%) 0.25 PMOS CURRENT (mA) 0.20 0.15 0.10 0.05 0 600 500 400 300 200 100 0 -100 IN SHUTDOWN IN START-UP AFTER START-UP
TA = 25C unless otherwise noted. Output Disconnect PMOS Current vs CAP to VOUT Voltage Difference
0
4
8 12 VCC VOLTAGE (V)
16
3495 G19
0
2 4 6 8 10 12 CAP TO VOUT VOLTAGE DIFFERENCE (V)
3495 G20
LT3495 Start-Up Waveforms
SHDN VOLTAGE 5V/DIV
INDUCTOR CURRENT 500mA/DIV
CAP VOLTAGE 5V/DIV VOUT VOLTAGE 5V/DIV VCC = 3.6V VOUT = 16V FIGURE 7 CIRCUIT 50s/DIV
3495 G21
LT3495 Transient Response
20mA 60mA 20mA LOAD PULSE VOUT VOLTAGE 200mV/DIV AC COUPLED
LT3495-1 Transient Response
10mA 30mA 10mA LOAD PULSE
VOUT VOLTAGE 200mV/DIV AC COUPLED
INDUCTOR CURRENT 500mA/DIV
INDUCTOR CURRENT 200mA/DIV
LOAD CURRENT 20mA/DIV 20s/DIV
3495 G22
LOAD CURRENT 20mA/DIV 20s/DIV
3495 G23
VCC = 3.6V VOUT = 16V FIGURE 7 CIRCUIT
VCC = 3.6V VOUT = 16V FIGURE 9 CIRCUIT
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LT3495/LT3495B/ LT3495-1/LT3495B-1 PIN FUNCTIONS
GND (Pins 1, 2): Ground. Tie directly to local ground plane. VCC (Pin 3): Input Supply Pin. Must be locally bypassed. CTRL (Pin 4): Dimming Pin. If not used, tie CTRL to 1.5V or higher. If in use, drive CTRL below 1.235V to override the internal reference. See Applications section for more information. SHDN (Pin 5): Shutdown Pin. Tie to 1.5V or more to enable chip. Ground to shut down. FB (Pin 6): Feedback Pin. Minimize the metal trace area to this pin to minimize noise. Reference voltage is 1.235V. There is an internal 76k resistor from the FB pin to GND. To achieve the desired output voltage, choose R1 according to the following formula: R1 = 76 * (VOUT/1.235 - 1)k VOUT (Pin 7): Drain of Output Disconnect PMOS. Place a bypass capacitor from this pin to GND. See Applications information. CAP (Pins 8, 9): Source of Output Disconnect PMOS. Place a bypass capacitor from this pin to GND. SW (Pin 10): Switch Pin. This is the collector of the internal NPN power switch. Minimize the metal trace area connected to this pin to minimize EMI. Exposed Pad (Pin 11): Ground. This pin must be soldered to PCB.
BLOCK DIAGRAM
INPUT R1 6 FB 3 VCC 10 SW 9 CAP 8 CAP 7 VOUT
76k
START-UP CONTROL
4 5
SHDN
+
VREF
+ +
CTRL
-
SWITCH CONTROL GND 2 1 GND 11
DISCONNECT CONTROL
SHUNT CONTROL
3495 BD
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LT3495/LT3495B/ LT3495-1/LT3495B-1 OPERATION
The LT3495 series utilizes a variable peak current, variable off-time control scheme to provide high efficiency over a wide range of output current. The operation of the part can be better understood by referring to the Block Diagram. The part senses the output voltage by monitoring the voltage on the FB pin. The user sets the desired output voltage by choosing the value of the external top feedback resistor. The parts incorporate a precision 76k bottom feedback resistor. Assuming that output voltage adjustment is not used (CTRL pin is tied to 1.5V or greater), the internal reference (VREF = 1.235V) sets the voltage at which FB will servo to during regulation. The Switch Control block senses the output of the amplifier and adjusts the switching frequency as well as other parameters to achieve regulation. During the start-up of the circuit, special precautions are taken to ensure that the inductor current remains under control. For the LT3495/LT3495-1, the switching frequency is never allowed to fall below approximately 45kHz. Because of this, a minimum load must be present to prevent the output voltage from drifting too high. For most applications, this minimum load is automatically generated within the part via the Shunt Control block. The level of this current is adaptable, removing itself when not needed to improve efficiency at higher load levels. However when the input voltage and output voltage are close, the internal shunt current may not be large enough. Under this condition, a minimum output load is required to prevent the output voltage from drifting too high. For the LT3495B/B-1, the minimum switching frequency feature is disabled and the switching frequency can be as low as zero. As a result, the output voltage will never drift high and no minimum output load is required. The LT3495 series also has a PMOS output disconnect switch. The PMOS switch is turned on when the part is enabled via the SHDN pin. When the parts are in shutdown, the PMOS switch turns off, allowing the VOUT node to go to ground. This type of disconnect function is often required in power supplies. The LT3495 series also sets a maximum switch on time of 10s. This feature guarantees that the parts can continue to deliver energy to the output even if the input supply impedance becomes so large that the commanded peak switch current is never reached. The difference between the LT3495/LT3495B and LT3495-1/ LT3495B-1 is the level of the current limit. LT3495/LT3495B have a typical peak current limit of 650mA while the LT3495-1/LT3495B-1 have a typical peak current limit of 350mA. The differences between the LT3495 and LT3495B/ LT3495-1/LT3495B-1 are listed in Table 1.
Table 1. Difference Between LT3495 and LT3495B/LT3495-1/LT3495B-1
PART LT3495 LT3495B LT3495-1 LT3495B-1 SWITCH CURRENT LIMIT (mA) 650 650 350 350 MINIMUM SWITCHING FREQUENCY (kHz) MINIMUM OUTPUT LOAD REQUIREMENT 45 0 45 0 Required under certain conditions Not Required Required under certain conditions Not Required
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LT3495/LT3495B/ LT3495-1/LT3495B-1 APPLICATIONS INFORMATION
Inductor Selection Several inductors that work well with the LT3495/LT3495B are listed in Table 2 and those for the LT3495-1/LT3495B-1 are listed in Table 3. These tables are not complete, and there are many other manufacturers and devices that can be used. Consult each manufacturer for more detailed information and for their entire selection of related parts, as many different sizes and shapes are available. Inductors with a value of 3.3H or higher are recommended for most LT3495 series designs. Inductors with low core losses and small DCR (copper wire resistance) are good choices for LT3495 series applications. For full output power, the inductor should have a saturation current rating higher than the peak inductor current. The peak inductor current can be calculated as: IPK =ILIMIT + VIN * 200 * 10 L
-9
input capacitor and a 1F to 10F output capacitor are sufficient for most applications. Always use a capacitor with a sufficient voltage rating. Many capacitors rated at 1F to 10F particularly 0603 case sizes, have greatly , reduced capacitance when bias voltages are applied. Be sure to check actual capacitance at the desired output voltage. Generally a 0805 or 1206 size capacitor will be adequate. A 2.2F capacitor placed on the CAP node is recommended to filter the inductor current while a 1F to 10F capacitor placed on the VOUT node will give excellent transient response and stability. Table 4 shows a list of several capacitor manufacturers. Consult the manufacturers for more detailed information and for their entire selection of related parts.
Table 3. Recommended Inductors for LT3495-1/LT3495B-1
PART L DCR (H) (m) 4.7 6.8 10 4.7 6.8 10 4.7 10 6.2 4.7 150 180 230 350 500 650 150 300 369 290 SIZE (mm) VENDOR
amps
where ILIMIT is 0.65A and 0.35A for LT3495/LT3495B and LT3495-1/LT3495B-1 respectively. L is the inductance value in Henrys and VIN is the input voltage to the boost circuit.
Table 2. Recommended Inductors for LT3495/LT3495B
PART LPS4018-103ML MSS5131-103MLC LPS3015-472MLC LPS3015-682MLC LQH43CN4R7M03 CR32-6R8 744031004 L DCR (H) (m) 10 10 4.7 6.8 4.7 6.8 4.7 200 83 200 300 150 202 105 SIZE (mm) VENDOR
LPO4815-472MLC LPO4815-682MLC LPO4815-103MLC LPS3008-472MLC LPS3008-682MLC LPS3008-103MLC LQH32CN4R7M53 LQH32CN100K33 CDH28D09/S-6R2 744030004
4.8 x 4.8 x 1.5 Coilcraft 4.8 x 4.8 x 1.5 www.coilcraft.com 4.8 x 4.8 x 1.5 3.0 x 3.0 x 0.8 3.0 x 3.0 x 0.8 3.0 x 3.0 x 0.8 3.2 x 2.5 x 1.6 Murata 3.2 x 2.5 x 2.0 www.murata.com 3.3 x 3.0 x 1.0 Sumida www.sumida.com 3.5 x 3.3 x 1.0 Wurth Elektronik www.weonline.com
4.4 x 4.4 x 1.7 Coilcraft 5.1 x 5.1 x 3.1 www.coilcraft.com 3.0 x 3.0 x 1.5 3.0 x 3.0 x 1.5 4.5 x 3.2 x 2.8 Murata www.murata.com 4.1 x 3.7 x 3.0 Sumida www.sumida.com 3.8 x 3.8 x 1.7 Wurth Elektronik www.weonline.com
Table 4. Recommended Ceramic Capacitor Manufacturers
MANUFACTURER Taiyo Yuden AVX Murata Kemet TDK PHONE (408) 573-4150 (843) 448-9411 (814) 237-1431 (408) 986-0424 (847) 803-6100 WEBSITE www.t-yuden.com www.avxcorp.com www.murata.com www.kemet.com www.tdk.com
Capacitor Selection The small size and low ESR of ceramic capacitors makes them suitable for most LT3495 series applications. X5R and X7R types are recommended because they retain their capacitance over wider voltage and temperature ranges than other types such as Y5V or Z5U. A 4.7F
Diode Selection Schottky diodes, with their low forward voltage drops and fast switching speeds, are recommended for use with the LT3495 series. The Diodes Inc. B0540WS-7 is a very good choice. This diode is rated to handle an average forward current of 0.5A with 40V reverse breakdown.
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LT3495/LT3495B/ LT3495-1/LT3495B-1 APPLICATIONS INFORMATION
Setting Output Voltage and the Auxiliary Reference Input The LT3495 series is equipped with both an internal 1.235V reference and an auxiliary reference input. This allows the user to select between using the built-in reference and supplying an external reference voltage. The voltage at the CTRL pin can be adjusted while the chip is operating to alter the output voltage for purposes such as display dimming or contrast adjustment. To use the internal 1.235V reference, the CTRL pin must be held higher than 1.5V. When the CTRL pin is held between 0V and 1.235V, the parts will regulate the output such that the FB pin voltage is nearly equal to the CTRL pin voltage. At CTRL voltages close to 1.235V, a soft transition occurs between the CTRL pin and the internal reference. Figure 1 shows this behavior. To set the maximum output voltage, select the values of R1 according to the following equation: R1= 76 * VOUT -1 k 1.235 Choosing a Feedback Node The single feedback resistor may be connected to the VOUT pin or to the CAP pin (see Figure 2). Regulating the VOUT pin eliminates the output offset resulting from the voltage drop across the output disconnect PMOS. Regulating the CAP pin does not compensate for the voltage drop across the output disconnect, resulting in an output voltage VOUT that is slightly lower than the voltage set by the resistor divider. Under most conditions, it is advised that the feedback resistor be tied to the VOUT pin. Connecting the Load to the CAP Node The efficiency of the converter can be improved by connecting the load to the CAP pin instead of the VOUT pin. The power loss in the PMOS disconnect circuit is then made negligible. By connecting the feedback resistor to the VOUT pin, no quiescent current will be consumed in the feedback resistor string during shutdown since the PMOS transistor will be open (see Figure 3). The disadvantage of this method is that the CAP node cannot go to ground during shutdown, but will be limited to around a diode drop below VCC. Loads connected to the part should only sink current. Never force external power supplies onto the CAP or VOUT pins.
C1 SW VCC SHDN CTRL 1.2 FB VOLTAGE (V) CAP VOUT R1 FB GND VOUT C3 SW VCC SHDN CTRL CAP VOUT R1 FB GND
3495 F02
When CTRL is used to override the internal reference, the output voltage can be lowered from the maximum value down to nearly the input voltage level. If the voltage source driving the CTRL pin is located at a distance to the LT3495, a small 0.1F capacitor may be needed to bypass the pin locally.
1.5
C1
LT3495
LT3495
0.9
Figure 2. Feedback Connection Using the CAP Pin or the VOUT Pin
0.6 SW 0.3 VCC SHDN CTRL
3495 F01
CAP VOUT FB GND
3495 F03
C1
ILOAD
LT3495 0 0 0.3 0.6 0.9 CTRL VOLTAGE (V) 1.2 1.5
Figure 1. CTRL to FB Transfer Curve
Figure 3. Improved Efficiency Connection
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LT3495/LT3495B/ LT3495-1/LT3495B-1 APPLICATIONS INFORMATION
Maximum Output Load Current The maximum output current of a particular LT3495 series circuit is a function of several circuit variables. The following method can be helpful in predicting the maximum load current for a given circuit: Step 1: Calculate the peak inductor current: IPK =ILIMIT + VIN * 200 * 10 -9 amps L Inrush Current When VCC is stepped from ground to the operating voltage while the output capacitor is discharged, a higher level of inrush current may flow through the inductor and Schottky diode into the output capacitor. Conditions that increase inrush current include a larger more abrupt voltage step at VIN, a larger output capacitor tied to the CAP pin and an inductor with a low saturation current. While the chip is designed to handle such events, the inrush current should not be allowed to exceed 1.5A. For circuits that use output capacitor values within the recommended range and have input voltages of less than 5V, inrush current remains low, posing no hazard to the device. In cases where there are large steps at VCC (more than 5V) and/or a large capacitor is used at the CAP pin, inrush current should be measured to ensure safe operation. Soft-Start By connecting the SHDN and CTRL pins as shown in Figure 4, using an RC filter at the CTRL pin to limit the start-up current, the LT3495 is able to achieve soft-start. The small bias current of the CTRL pin allows using a small capacitor for a large RC time constant. The softstart waveform is shown in Figure 5. The soft-start time
SW CAP VOUT FB GND
3495 F04
where ILIMIT is 0.65A and 0.35A for LT3495/LT3495B and LT3495-1/LT3495B-1 respectively. L is the inductance value in Henrys and VIN is the input voltage to the boost circuit. Step 2: Calculate the inductor ripple current: IRIPPLE
( VOUT + 1- VIN ) * 200 * 10 -9 amps =
L
where VOUT is the desired output voltage. If the inductor ripple current is greater than the peak current, then the circuit will only operate in discontinuous conduction mode. The inductor value should be increased so that IRIPPLE < IPK. An application circuit can be designed to operate only in discontinuous mode, but the output current capability will be reduced. Step 3: Calculate the average input current: IIN(AVG) =IPK - IRIPPLE amps 2
VCC CHIP ENABLE RCTRL CCTRL SHDN CTRL
LT3495
Step 4: Calculate the nominal output current: IOUT(NOM) = IIN(AVG) * VIN * 0.8 VOUT amps
SHDN VOLTAGE 5V/DIV INDUCTOR CURRENT 500mA/DIV CTRL VOLTAGE 2V/DIV VOUT VOLTAGE 5V/DIV
Figure 4. Soft-Start Circuitry
Step 5: Derate output current: IOUT = IOUT(NOM) * 0.8 amps For low output voltages the output current capability will be increased. When using output disconnect (load current taken from VOUT), these higher currents will cause the drop in the PMOS switch to be higher resulting in reduced output current capability than those predicted by the preceding equations.
VCC = 3.6V VOUT = 16V
500s/DIV
3495 F05
Figure 5. Soft-Start Waveform
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LT3495/LT3495B/ LT3495-1/LT3495B-1 APPLICATIONS INFORMATION
can be set by the value of RCTRL and CCTRL. The following expression can be used to design the soft-start time: TSTART
UP
= RCTRL * CCTRL *In
VSHDN VSHDN - 1.235
Also be aware of the thermal dissipation in the PMOS at all times. In addition, if the input voltage is more than 8V, the PMOS will turn on during shutdown, resulting in the output voltage no longer being blocked from the input. Under this condition, the output voltage will be about 8V lower than the input voltage. Board Layout Considerations As with all switching regulators, careful attention must be paid to the PCB board layout and component placement. To maximize efficiency, switch rise and fall times are made as short as possible. To prevent electromagnetic interference (EMI) problems, proper layout of the high frequency switching path is essential. The voltage signal of the SW pin has sharp rising and falling edges. Minimize the length and area of all traces connected to the SW pin and always use a ground plane under the switching regulator to minimize interplane coupling. In addition, the FB pin feeds into the internal error amplifier and is sensitive to noise. Minimizing the length and area of all traces to this pin is recommended. Connect the feedback resistor R1 directly from the VOUT pin to the FB pin and keep the trace as short as possible. Recommended component placement is shown in Figure 6.
where VSHDN is the voltage at SHDN pin when the part is enabled. To ensure soft-start will work, the initial voltage at CTRL pin when the part is enabled should be close to 0V. The soft-start may not work if this initial condition is not satisfied. Output Disconnect The LT3495 series has an output disconnect PMOS that blocks the load from the input during shutdown. During normal operation, the maximum current through the PMOS is limited by circuitry inside the chip. When the CAP and VOUT voltage difference is more than 8.7V (typ), the current through the PMOS is no longer limited, and can be much higher. As a result, forcing 8.7V or higher voltage from the CAP to the VOUT pins can damage the PMOS. In cases when the CAP voltage is high and/or a large capacitor is used at the CAP pin, shorting VOUT to GND can cause large PMOS currents to flow. Under this condition, the PMOS peak current should be kept at less than 1A.
GND GND VCC CTRL SHDN GND GND
SW CAP CAP VOUT FB
3495 F06
CTRL SHDN VIAS TO GROUND PLANE REQUIRED TO IMPROVE THERMAL PERFORMANCE VIAS FOR CAP GROUND RETURN THROUGH SECOND METAL LAYER, CAPACITOR GROUNDS MUST BE RETURNED DIRECTLY TO IC GROUND
Figure 6. Recommended Board Layout
3495b1b1f
12
LT3495/LT3495B/ LT3495-1/LT3495B-1 TYPICAL APPLICATIONS
L1 10H ONE Li-Ion CELL C1 4.7F D1 C2 2.2F OUTPUT 16V 70mA R1 909k FB GND
3495 F07a
Efficiency vs Load Current
90 CAP VOUT C3 1F VIN = 3.6V 400 LOAD FROM CAP LOAD FROM VOUT 320 POWER LOSS (mW)
SW VCC
80 EFFICIENCY (%)
LT3495
70
240
TURN ON/OFF VOUT DIMMING
SHDN CTRL
60
160
50
80
C1: 4.7F 6.3V, X5R, 0603 , C2: 2.2F 25V, X5R, 0805 , C3: 1F 25V, X5R, 0603 , D1: DIODES INC. B0540WS-7 L1: COILCRAFT LPS4018-103MLB
40 0.1
1 10 LOAD CURRENT (mA)
0 100
3495 F07b
Figure 7. One Li-Ion Cell Input Boost Converter with the LT3495
L1 6.8H ONE Li-Ion CELL C1 4.7F
Efficiency vs Load Current
D1 C2 2.2F OUTPUT 16V 70mA R1 909k FB GND
3495 F08a
90 CAP
VIN = 3.6V
400 LOAD FROM CAP 320 LOAD FROM VOUT POWER LOSS (mW)
SW VCC
80 EFFICIENCY (%)
VOUT C3 1F
LT3495B
70
240
TURN ON/OFF VOUT DIMMING
SHDN CTRL
60
160
50
80
C1: 4.7F 6.3V, X5R, 0603 , C2: 2.2F 25V, X5R, 0805 , C3: 1F 25V, X5R, 0603 , D1: DIODES INC. B0540WS-7 L1: SUMIDA CR32-6R8
40 0.1
1 10 LOAD CURRENT (mA)
0 100
3495 F08b
Figure 8. One Li-Ion Cell Input Boost Converter with the LT3495B
LT3495/LT3495B Maximum Output Current vs Output Voltage
VOUT 40 35 30 25 20 15 10 5 R1 VALUE REQUIRED (M) 2.37 2.05 1.78 1.47 1.15 0.845 0.536 0.232 MAXIMUM OUTPUT CURRENT AT 3V INPUT (mA) 26 31 37 43 57 74 120 250
3495b1b1f
13
LT3495/LT3495B/ LT3495-1/LT3495B-1 TYPICAL APPLICATIONS
L1 10H ONE LI-ION CELL C1 2.2F
Efficiency vs Load Current
D1 C2 1F OUTPUT 16V 30mA 909k C3 1F 80 EFFICIENCY (%) 90 CAP VOUT VIN = 3.6V 250 LOAD FROM CAP 200 POWER LOSS (mW)
SW VCC
LT3495B-1/ LT3495-1 TURN ON/OFF VOUT DIMMING SHDN CTRL FB GND
70 LOAD FROM VOUT 60
150
100
3495 F09a
50
50
C1: 2.2F 6.3V, X5R, 0603 , C2: 1F 25V, X5R, 0603 , C3: 1F 25V, X5R, 0603 , D1: DIODES INC. B0540WS-7 L1: MURATA LQH32CN100K33
40 0.1
1 10 LOAD CURRENT (mA)
0 100
3495 F09b
Figure 9. One Li-Ion Cell Input Boost Converter with the LT3495-1/LT3495B-1 LT3495-1/LT3495B-1 Maximum Output Current vs Output Voltage
VOUT 40 35 30 25 20 15 10 5 R1 VALUE REQUIRED (M) 2.37 2.05 1.78 1.47 1.15 0.845 0.536 0.232 MAXIMUM OUTPUT CURRENT AT 3V INPUT (mA) 12 15 18 21 28 36 63 120
5V to 12V, 130mA Boost Converter
100 L1 10H VIN = 5V C1 4.7F D1 C2 2.2F VOUT = 12V 130mA 665k C3 10F 90 EFFICIENCY (%) CAP VOUT 80 70 60 50
3495 TA02a
Efficiency vs Load Current
900 LOAD FROM CAP LOAD FROM VOUT 750 POWER LOSS (mW) 600 450 300 150 0 1000
3495 TA02b
SW VCC
LT3495B
TURN ON/OFF VOUT DIMMING
SHDN CTRL
FB GND
C1: 4.7F 6.3V, X5R, 0603 , C2: 2.2F 25V, X5R, 0805 , C3: 10F 25V, X5R, 1206 , D1: DIODES INC. B0540WS-7 L1: COILCRAFT LPS4018-103MLB
40 0.1
1
10 100 LOAD CURRENT (mA)
3495b1b1f
14
LT3495/LT3495B/ LT3495-1/LT3495B-1 TYPICAL APPLICATIONS
Wide Input Range SEPIC Converter with 5V Output
L1 10H C1 2.2F C2 1F 90 D1 80 SW VCC CAP VOUT EFFICIENCY (%) L2 10H C3 10F
Efficiency vs Load Current
VCC = 3.3V 1200 1000 POWER LOSS (mW) 800 70 600 60 400 50 200 0 1000
3495 TA03b
INPUT 2.6V TO 12V
LT3495B 232k FB GND
3495 TA03a
VOUT = 5V 200mA, VIN = 3.3V, 300mA, VIN = 5V, 500mA, VIN = 8V
TURN ON/OFF VOUT DIMMING
SHDN CTRL
C1: 2.2F 16V, X5R, 0805 , C2: 1F 16V, X5R, 0805 , C3: 10F 16V, X5R, 1206 , D1: FAIRCHILD SEMI MBR0540 L1, L2: COILCRAFT LPS4018-103MLB
40 0.1
1
10 100 LOAD CURRENT (mA)
PACKAGE DESCRIPTION
DDB Package 10-Lead Plastic DFN (3mm x 2mm)
(Reference LTC DWG # 05-08-1722 Rev O)
0.64 0.05 (2 SIDES) 0.70 0.05 2.55 0.05 1.15 0.05 PACKAGE OUTLINE 0.25 0.05 0.50 BSC 2.39 0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS NOTE: 1. DRAWING CONFORMS TO VERSION (WECD-1) IN JEDEC PACKAGE OUTLINE M0-229 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 PIN 1 BAR TOP MARK (SEE NOTE 6) 2.00 0.10 (2 SIDES) 0.64 0.05 (2 SIDES) 5 0.25 0.05 2.39 0.05 (2 SIDES) BOTTOM VIEW--EXPOSED PAD PIN 1 R = 0.20 OR 0.25 x 45 CHAMFER
(DDB10) DFN 0905 REV O
3.00 0.10 (2 SIDES)
R = 0.05 TYP
R = 0.115 TYP 6
0.40 0.10 10
1
0.200 REF
0.75 0.05
0.50 BSC
0 - 0.05
3495b1b1f
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.
15
LT3495/LT3495B/ LT3495-1/LT3495B-1 TYPICAL APPLICATION
Adjustable High Voltage Power Supply Doesn't Need a Transformer
DANGER HIGH VOLTAGE! OPERATION BY HIGH VOLTAGE TRAINED PERSONNEL ONLY C4 1F L1 22H C1 4.7F D5 C2 1F C6 1F 150
Output vs CTRL
120 VOUT VOLTAGE (V)
3.3V TO 8V INPUT
D1 CAP VOUT C3 1F FB GND
3495 TA04a
D2
D3 C7 1F
D4
90
SW VCC
C5 1F
60
LT3495B TURN ON/OFF VOUT DIMMING SHDN CTRL
909k 10.7k
VOUT 15V TO 120V 10mA (VIN = 3.3V) 18mA (VIN = 5V) 35mA (VIN = 8V)
30
0
0
0.3
C1: 4.7F 16V, X5R, 0805 , C2-C7: 1F 50V, X5R, 0805 , D1-D5: DIODE INC. B0540WS-7 L1: COILCRAFT LPS4018-223MLB
0.6 0.9 1.2 1.5 CTRL VOLTAGE (V)
1.8
2.1
3495 TA04b
Efficiency vs Load Current
90 80 EFFICIENCY (%) 70 60 50 40 30 0.1 VIN = 5V VOUT = 120V 600 500 POWER LOSS (mW) 400 300 200 100 0 100
3495 TA04c
Output Voltage Ripple vs Load Current
700 VOUT PEAK-TO-PEAK RIPPLE (mV) 600 500 400 300 200 100 0 VIN = 5V VOUT = 120V
1 10 LOAD CURRENT (mA)
0
4
8 16 12 LOAD CURRENT (mA)
20
3495 TA04d
RELATED PARTS
PART NUMBER LT1930/LT1930A LT1945 (Dual) LT1946/LT1946A LT3463/LT3463A DESCRIPTION 1A (ISW), 1.2MHz/2.2MHz, High Efficiency Step-Up DC/DC Converters Dual Output, Boost/Inverter, 350mA (ISW), Constant OffTime, High Efficiency Step-Up DC/DC Converter 1.5A (ISW), 1.2MHz/2.7MHz, High Efficiency Step-Up DC/DC Converters COMMENTS VIN: 2.6V to 16V, VOUT(MAX) = 34V, IQ = 4.2mA/5.5mA, ISD <1A, ThinSOT Package VIN: 1.2V to 15V, VOUT(MAX) = 34V, IQ = 40A, ISD <1A, 10-Lead MS Package VIN: 2.45V to 16V, VOUT(MAX) = 34V, IQ = 3.2mA, ISD <1A, 8-Lead MS Package
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3495b1b1f LT 0708 * PRINTED IN USA
LT3467/LT3467A LT3471 LT3473/LT3473A
LT3494/LT3494A LT3580
16 Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
1630 McCarthy Blvd., Milpitas, CA 95035-7417
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2008

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