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LTC3443 High Current Micropower 600kHz Synchronous Buck-Boost DC/DC Converter
FEATURES

DESCRIPTIO
Regulated Output with Input Above, Below or Equal to the Output Single Inductor, No Schottky Diodes High Efficiency: Up to 96% 28A Quiescent Current in Burst Mode(R) Operation Up to 1.2A Continuous Output Current from a Single Lithium-Ion True Output Disconnect in Shutdown 2.4V to 5.5V Input Range 2.4V to 5.25V Output Range 600kHz Fixed Frequency Operation Synchronizable Oscillator Selectable Burst Mode or Fixed Frequency Operation <1A Quiescent Current in Shutdown Small, Thermally Enhanced 12-Lead (4mm x 3mm x 0.8mm) DFN package
The LTC(R)3443 is a high efficiency, fixed frequency, buckboost DC/DC converter that operates from input voltages above, below or equal to the output voltage. The part is pin for pin compatible with its predecessor, the LTC3441, with a lower operating frequency (600kHz), and a VC pin clamp circuit during Burst Mode operation. The topology incorporated in the IC provides a continuous transfer function through all operating modes, making the product ideal for single Lithium Ion or multicell applications where the output voltage is within the battery voltage range. The device includes two 0.10 N-channel MOSFET switches and two 0.11 P-channel switches. External Schottky diodes are optional, and can be used for a moderate efficiency improvement. The operating frequency is internally set to 600kHz and can be synchronized up to 1.2MHz. Quiescent current is only 28A in Burst Mode operation, maximizing battery life in portable applications. Burst Mode operation is user controlled and can be enabled by driving the MODE/SYNC pin high. If the MODE/ SYNC pin is driven low or with a clock, then fixed frequency switching is enabled. Other features include a 1A shutdown, soft-start control, thermal shutdown and current limit. The LTC3443 is available in a thermally enhanced 12-lead (4mm x 3mm) DFN Package.
APPLICATIO S

Handheld Computers Handheld Instruments MP3 Players Digital Cameras
, LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode is a registered trademark of Linear Technology Corporation. U.S. Patent #'s 6404251, 6166527
TYPICAL APPLICATIO
6H
Li-Ion to 3.3V at 1A Buck-Boost Converter
220pF SW1 VIN 2.5V TO 4.2V Li-Ion 10F PVIN SW2 340k
EFFICIENCY (%)
VOUT 3.3V 1A
100 95 90 85 80 75 70 65 60 55
VOUT LTC3443 VIN FB SHDN/SS VC
2.2k 15k 560pF 200k 44F (2 x 22F)
MODE/SYNC GND PGND PGND
3443 TA01
50
2.7
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Efficiency vs VIN
IOUT = 200mA IOUT = 1A VOUT = 3.3V 3.2 3.7 4.2 VIN (V) 4.7 5.2
3443 TA02
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LTC3443
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW SHDN/SS GND PGND SW1 SW2 PGND 1 2 3 4 5 6 13 12 FB 11 VC 10 VIN 9 8 7 PVIN VOUT MODE/SYNC
VIN, VOUT Voltage........................................ - 0.3V to 6V SW1, SW2 Voltage DC ...........................................................- 0.3V to 6V Pulsed < 100ns ...................................... - 0.3V to 7V SHDN/SS, MODE/SYNC Voltage ................. - 0.3V to 6V Operating Temperature Range (Note 2) .. - 40C to 85C Maximum Junction Temperature (Note 4) ........... 125C Storage Temperature Range ................ - 65C to 125C
ORDER PART NUMBER LTC3443EDE
DE12 PACKAGE 12-LEAD (4mm x 3mm) PLASTIC DFN TJMAX = 125C JA = 53C/W 1-LAYER BOARD JA = 43C/W 4-LAYER BOARD JC = 4.3C/W EXPOSED PAD IS PGND (PIN 13) MUST BE SOLDERED TO PCB
DE PART MARKING 3443
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
PARAMETER Input Start-Up Voltage Output Voltage Adjust Range Feedback Voltage Feedback Input Current Quiescent Current--Burst Mode Operation Quiescent Current--SHDN Quiescent Current--Active NMOS Switch Leakage PMOS Switch Leakage NMOS Switch On Resistance PMOS Switch On Resistance Input Current Limit Max Duty Cycle Min Duty Cycle Frequency Accuracy MODE/SYNC Threshold MODE/SYNC Input Current Error Amp AVOL Error Amp Source Current Error Amp Sink Current SHDN/SS Threshold SHDN/SS Threshold SHDN/SS Input Current VFB = 1.22V CONDITIONS
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = VOUT = 3.6V,unless otherwise noted.
MIN

TYP 2.3
MAX 2.4 5.25 1.25 50 45 1 900 7 10
UNITS V V V nA A A A A A A % %
2.4 1.19 1.22 1 28 0.1 520 0.1 0.1 0.10 0.11
VC = 0V, MODE/SYNC = 3V (Note 3) VOUT = SHDN = 0V, Not Including Switch Leakage MODE/SYNC = 0V (Note 3) Switches B and C Switches A and D Switches B and C Switches A and D
2 70 100 510 0.4
3.2 88 0 600 0.01 90 14 300 690 1.4 1
Boost (% Switch C On) Buck (% Switch A In)

VMODE/SYNC = 5.5V
When IC is Enabled When EA is at Max Boost Duty Cycle VSHDN = 5.5V
0.4
1 2 0.01
1.4 2.4 1
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% kHz V A dB A A V V A
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LTC3443
ELECTRICAL CHARACTERISTICS
Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The LTC3443E is guaranteed to meet performance specifications from 0C to 70C. Specifications over the -40C to 85C operating temperature range are assured by design, characterization and correlation with statistical process controls. Note 3: Current measurements are performed when the outputs are not switching. Note 4: This IC 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 result in device degradation or failure.
TYPICAL PERFOR A CE CHARACTERISTICS
Li-Ion to 3.3V Efficiency
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 0.1 1.0 10 100 OUTPUT CURRENT (mA) 1000
3443 G01
Burst Mode OPERATION VIN = 4.2V VIN = 3.3V VOUT 200mV/DIV AC-COUPLED MODE 5V/DIV VOUT = 3.3V VIN = 3.3V IOUT = 30mA 500s/DIV
3443 G03
VIN = 2.7V
VOUT Ripple at 1A Load
BUCK VIN = 4.2V VOUT 20mV/DIV AC-COUPLED BUCK-BOOST VIN = 3.3V BOOST VIN = 2.7V 1A IOUT = 1A VOUT = 3.3V 2s/DIV
3443 G02
UW
(TA = 25C unless otherwise specified) MODE Transient Response: Fixed Frequency to Burst Mode Operation
MODE Transient Response: Burst Mode Operation to Fixed Frequency
VOUT 100mV/DIV AC-COUPLED MODE 5V/DIV VOUT = 3.3V VIN = 3.3V IOUT = 30mA 500s/DIV
3443 G03
Load Transient Response, 100mA to 1A
VOUT 100mV/DIV
100mA 100s/DIV
3443 G03
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LTC3443 TYPICAL PERFOR A CE CHARACTERISTICS
Switch Pins in Buck-Boost Mode
SW1 2V/DIV
SW2 2V/DIV
VIN = 3.3V VOUT = 3.3V IOUT = 500mA
Switch Pins Before Entering Boost Mode
630 620
VIN + VOUT CURRENT (A)
600 590 580 570 560 550 540 530 520 -55 -25 5 35 65 TEMPERATURE (C) 95 125
3443 G07
SW2 2V/DIV
VIN = 3V VOUT = 3.3V IOUT = 500mA
50ns/DIV
3443 G06
FEEDBACK VOLTAGE (V)
SW1 2V/DIV
Burst Mode Quiescent Current
50 VIN = VOUT = 3.6V
LINE REGULATION (dB)
40
80
EA SOURCE CURRENT (A)
VIN + VOUT CURRENT (A)
30
20
10 -55
-25
5 35 65 TEMPERATURE (C)
4
UW
95
3443 G09
(TA = 25C unless otherwise specified)
Switch Pins Entering Buck-Boost Mode
SW1 2V/DIV
SW2 2V/DIV
50ns/DIV
3443 G04
VIN = 4.2V VOUT = 3.3V IOUT = 500mA
50ns/DIV
3443 G05
Active Quiescent Current
VIN = VOUT = 3.6V
1.241 1.236 1.231 1.226 1.221 1.216 1.211 1.206 1.201
Feedback Voltage
VIN = VOUT = 3.6V
610
1.196 -55
-25
5 35 65 TEMPERATURE (C)
95
125
3443 G08
Feedback Voltage Line Regulation
90 VIN = VOUT = 2.4V TO 5.5V
20
Error Amp Source Current
VIN = VOUT = 3.6V
15
70
10
125
60 -55
-25
5 35 65 TEMPERATURE (C)
95
125
3443 G10
5 -55
-25
5 35 65 TEMPERATURE (C)
95
125
3443 G11
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LTC3443 TYPICAL PERFOR A CE CHARACTERISTICS
Error Amp Sink Current
400 VIN = VOUT = 3.6V 0.70
EA SINK CURRENT (A)
350
FREQUENCY (MHz)
CURRENT LIMIT (A)
300
250
200 -55
-25
5 35 65 TEMPERATURE (C)
NMOS RDS(ON)
0.15 VIN = VOUT = 3.6V SWITCHES B AND C 0.13 0.15
0.13 PMOS RDS(ON) ()
MINIMUM START VOLTAGE (V)
NMOS RDS(ON) ()
0.11
0.09
0.07
0.05 -55
-25
5 35 65 TEMPERATURE (C)
PI FU CTIO S
SHDN/SS (Pin 1): Combined Soft-Start and Shutdown. Applied voltage < 0.4V shuts down the IC. Tie to >1.4V to enable the IC and >2.4V to ensure the error amp is not clamped from soft-start. An RC from the shutdown command signal to this pin will provide a soft-start function by limiting the rise time of the VC pin. GND (Pin 2): Signal Ground for the IC. PGND (Pins 3, 6, 13 Exposed Pad): Power Ground for the Internal NMOS Power Switches. The exposed pad must be soldered to PCB ground for optimal thermal performance. SW1 (Pin 4): Switch pin where the internal switches A and B are connected. Connect inductor from SW1 to SW2. An optional Schottky diode can be connected from this SW1 to ground. Minimize trace length to keep EMI down. SW2 (Pin 5): Switch pin where the internal switches C and D are connected. An optional Schottky diode can be connected from SW2 to VOUT (it is required where VOUT > 4.3V). Minimize trace length to keep EMI down. MODE/SYNC (Pin 7): Burst Mode Select and Oscillator Synchronization. MODE/SYNC = High: Enable Burst Mode Operation. During the period where the IC is supplying energy to the output, the inductor peak inductor current will reach 0.8A and return to zero current on each cycle. In Burst Mode operation the operation is variable frequency, which provides a significant efficiency improvement at light loads. The Burst Mode operation will continue until the pin is driven low.
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95
3443 G12
(TA = 25C unless otherwise specified) Current Limit
3.4 VIN = VOUT = 3.6V
Output Frequency
VIN = VOUT = 3.6V
0.65
3.2
0.60
3.0
0.55
125
0.50 -55
-25
5 35 65 TEMPERATURE (C)
95
125
3443 G13
2.8 -55
-25
5 35 65 TEMPERATURE (C)
95
125
3443 G14
PMOS RDS(ON)
VIN = VOUT = 3.6V SWITCHES A AND D
2.30
Minimum Start Voltage
2.25
0.11
2.20
0.09
2.15
0.07
95
125
3443 G15
0.05 -50
-25
35 65 5 TEMPERATURE (C)
95
125
3443 G16
2.10 -55
-25
5 35 65 TEMPERATURE (C)
95
125
3443 G17
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LTC3443
PI FU CTIO S
MODE/SYNC = Low: Disable Burst Mode operation and maintain low noise, constant frequency operation . MODE/SYNC = External CLK : Synchronization of the internal oscillator and Burst Mode operation disable. A clock pulse width between 100ns and 2s and a clock frequency between 1.38MHz and 2.4MHz (twice the desired frequency) is required to synchronize the IC. fOSC = fSYNC/2 VOUT (Pin 8): Output of the Synchronous Rectifier. A filter capacitor is placed from VOUT to GND. A ceramic bypass capacitor is recommended as close to the VOUT and GND pins as possible. PVIN (Pin 9): Power VIN Supply Pin. A 10F ceramic capacitor is recommended as close to the PVIN and PGND pins as possible VIN (Pin 10): Input Supply Pin. Internal VCC for the IC. VC (Pin 11): Error Amp Output. A frequency compensation network is connected from this pin to the FB pin to compensate the loop. See the section "Compensating the Feedback Loop" for guidelines. FB (Pin 12): Feedback Pin. Connect resistor divider tap here. The output voltage can be adjusted from 2.4V to 5.25V. The feedback reference voltage is typically 1.22V.
BLOCK DIAGRA
VIN 2.4V TO 5.5V 9
PVIN VIN
+
10
ISENSE AMP
+
gm = 1 k 100 3.2A PGND
-
AVERAGE CURRENT LIMIT THERMAL SHUTDOWN CLAMP MODE
SUPPLY CURRENT LIMIT
+
4A VCC INTERNAL
-
UVLO
+
2.4V
-
600kHz OSC SYNC SLEEP /2 5s DELAY 7 MODE/SYNC 2 GND 6 PGND Burst Mode OPERATION CONTROL SHUTDOWN
1 = Burst Mode OPERATION 0 = FIXED FREQUENCY
6
-
PWM LOGIC AND OUTPUT PHASING
PWM COMPARATORS CLAMP
+
-
-
+
+
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SW1 SW A
4
5
SW2
SW D
VOUT
VOUT 2.4V TO 5.25V 8
SW B
GATE DRIVERS AND ANTICROSS CONDUCTION
-0.4A SW C
REVERSE CURRENT LIMIT
ERROR AMP
+ -
1.22V R1 FB 12
VC
11 R2
SHDN/SS
RSS 1 VIN
CSS
3443 BD
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LTC3443
OPERATIO
The LTC3443 provides high efficiency, low noise power for applications such as portable instrumentation. The LTC proprietary topology allows input voltages above, below or equal to the output voltage by properly phasing the output switches. The error amp output voltage on the VC pin determines the output duty cycle of the switches. Since the VC pin is a filtered signal, it provides rejection of frequencies from well below the switching frequency. The low RDS(ON), low gate charge synchronous switches provide high frequency pulse width modulation control at high efficiency. Schottky diodes across the synchronous switch D and synchronous switch B are not required, but provide a lower drop during the break-before-make time (typically 15ns). The addition of the Schottky diodes will improve peak efficiency by typically 1% to 2%. High efficiency is achieved at light loads when Burst Mode operation is entered and when the IC's quiescent current is a low 28A. LOW NOISE FIXED FREQUENCY OPERATION Oscillator The frequency of operation is factory trimmed to 600kHz. The oscillator can be synchronized with an external clock applied to the MODE/SYNC pin. A clock frequency of twice the desired switching frequency and with a pulse width of at least 100ns is applied. The oscillator sync range is 690kHz to 1.2MHz (1.38MHz to 2.4MHz sync frequency). Error Amp The error amplifier is a voltage mode amplifier. The loop compensation components are configured around the amplifier to obtain stability of the converter. The SHDN/SS pin will clamp the error amp output, VC, to provide a softstart function.
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Supply Current Limit The current limit amplifier will shut PMOS switch A off once the current exceeds 4A typical. Before the switch current limit, the average current limit amp (3.2A typical) will source current into the FB pin to drop the output voltage. The current amplifier delay to output is typically 50ns. Reverse Current Limit The reverse current limit amplifier monitors the inductor current from the output through switch D. Once a negative inductor current exceeds - 400mA typical, the IC will shut off switch D. Output Switch Control Figure 1 shows a simplified diagram of how the four internal switches are connected to the inductor, VIN, VOUT and GND. Figure 2 shows the regions of operation for the LTC3443 as a function of the internal control voltage, VCI. The VCI voltage is a level shifted voltage from the output of the error amp (VC pin) (see Figure 5). The output switches are properly phased so the transfer between operation modes is continuous, filtered and transparent to the user. When VIN approaches VOUT the Buck/Boost region is reached where the conduction time of the four switch region is typically 150ns. Referring to Figures 1 and 2, the various regions of operation will now be described. Buck Region (VIN > VOUT) Switch D is always on and switch C is always off during this mode. When the internal control voltage, VCI, is above voltage V1, output A begins to switch. During the off time of switch A, synchronous switch B turns on for the remainder of the time. Switches A and B will alternate
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LTC3443
OPERATIO
8
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PVIN 9 PMOS A SW1 4 NMOS B SW2 5 NMOS C VOUT 8 VOUT PMOS D
3443 F01
Figure 1. Simplified Diagram of Output Switches
75% DMAX BOOST A ON, B OFF BOOST REGION PWM CD SWITCHES DMIN BOOST DMAX BUCK FOUR SWITCH PWM BUCK/BOOST REGION
D ON, C OFF PWM AB SWITCHES BUCK REGION 0% DUTY CYCLE
3443 F02
Figure 2. Switch Control vs Internal Control Voltage, VCI
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LTC3443
OPERATIO
similar to a typical synchronous buck regulator. As the control voltage increases, the duty cycle of switch A increases until the maximum duty cycle of the converter in Buck mode reaches DMAX_BUCK, given by: DMAX_BUCK = 100 - D4SW % where D4SW = duty cycle % of the four switch range. D4SW = (150ns * f) * 100 % where f = operating frequency, Hz. Beyond this point the "four switch," or Buck/Boost region is reached. Buck/Boost or Four Switch (VIN ~ VOUT) When the internal control voltage, VCI, is above voltage V2, switch pair AD remain on for duty cycle DMAX_BUCK, and the switch pair AC begins to phase in. As switch pair AC phases in, switch pair BD phases out accordingly. When the VCI voltage reaches the edge of the Buck/Boost range, at voltage V3, the AC switch pair completely phase out the BD pair, and the boost phase begins at duty cycle D4SW. The input voltage, VIN, where the four switch region begins is given by:
VIN =
VOUT V 1 - (150ns * f)
The point at which the four switch region ends is given by: VIN = VOUT(1 - D) = VOUT(1 - 150ns * f) V Boost Region (VIN < VOUT) Switch A is always on and switch B is always off during this mode. When the internal control voltage, VCI, is above voltage V3, switch pair CD will alternately switch to provide a boosted output voltage. This operation is typical to a synchronous boost regulator. The maximum duty cycle of the converter is limited to 88% typical and is reached when VCI is above V4.
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Burst Mode OPERATION Burst Mode operation is when the IC delivers energy to the output until it is regulated and then goes into a sleep mode where the outputs are off and the IC is consuming only 28A. In this mode the output ripple has a variable frequency component that depends upon load current. During the period where the device is delivering energy to the output, the peak current will be equal to 800mA typical and the inductor current will terminate at zero current for each cycle. In this mode the typical maximum average output current is given by:
IOUT(MAX)BURST
0.2 * VIN A VOUT + VIN
Burst Mode operation is user controlled, by driving the MODE/SYNC pin high to enable and low to disable. The peak efficiency during Burst Mode operation is less than the peak efficiency during fixed frequency because the part enters full-time 4-switch mode (when servicing the output) with discontinuous inductor current as illustrated in Figures 3 and 4. During Burst Mode operation, the control loop is nonlinear and cannot utilize the control voltage from the error amp to determine the control mode, therefore full-time 4-switch mode is required to maintain the Buck/Boost function. The efficiency below 1mA becomes dominated primarily by the quiescent current and not the peak efficiency. The equation is given by:
Efficiency Burst ( bm) * ILOAD 25A + ILOAD
where (bm) is typically 80% during Burst Mode operation.
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LTC3443
OPERATIO
SOFT-START The soft-start function is combined with shutdown. When the SHDN/SS pin is brought above typically 1V, the IC is enabled but the EA duty cycle is clamped from the VC pin.
PVIN 9 A 4 SW1 B dI VIN L dt L D VOUT 8 A IINDUCTOR 800mA 4 SW1 B 0mA T1 6 GND
3443 F03
+
-
SW2 C
L
SW2 C
IINDUCTOR
Figure 3. Inductor Charge Cycle During Burst Mode Operation
TO PWM COMPARATORS
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A detailed diagram of this function is shown in Figure 5. The components RSS and CSS provide a slow ramping voltage on the SHDN/SS pin to provide a soft-start function.
PVIN 9 dI - VOUT L dt D 5 800mA VOUT 8 5
-
+
0mA T2
3443 F04
6 GND
Figure 4. Inductor Discharge Cycle During Burst Mode Operation
VIN 14A
ERROR AMP VOUT FB R1
+ -
SOFT-START CLAMP VCI
1.22V
12 VC 11 CP1 R2
SHDN/SS 1 CSS
RSS ENABLE SIGNAL
3443 F05
+
CHIP ENABLE
-
1V
Figure 5. Soft-Start Circuitry
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LTC3443
APPLICATIO S I FOR ATIO
COMPONENT SELECTION
1 SHDN/SS 2 GND 3 PGND 4 SW1 5 SW2 6 PGND FB 12 VC 11 VIN 10 PVIN 9 VOUT 8 MODE 7 VOUT VIN
GND
MULTIPLE VIAS
Figure 6. Recommended Component Placement. Traces Carrying High Current are Direct. Trace Area at FB and VC Pins are Kept Low. Lead Length to Battery Should be Kept Short. VOUT and VIN Ceramic Capacitors Close to the IC Pins
Inductor Selection The high frequency operation of the LTC3443 allows the use of small surface mount inductors. The inductor current ripple is typically set to 20% to 40% of the maximum inductor current. For a given ripple the inductance terms are given as follows:
L> L> VIN(MIN)2 * VOUT - VIN(MIN) * 100
(
)
f * IOUT(MAX) * %Ripple * VOUT
2
H,
VOUT * VIN(MAX) - VOUT * 100 f * IOUT(MAX) * %Ripple * VIN(MAX)
(
)
H
where f = operating frequency, Hz %Ripple = allowable inductor current ripple, % VIN(MIN) = minimum input voltage, V VIN(MAX) = maximum input voltage, V VOUT = output voltage, V IOUT(MAX) = maximum output load current
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For high efficiency, choose an inductor with a high frequency core material, such as ferrite, to reduce core loses. The inductor should have low ESR (equivalent series resistance) to reduce the I2R losses, and must be able to handle the peak inductor current without saturating. Molded chokes or chip inductors usually do not have enough core to support the peak inductor currents in the 1A to 2A region. To minimize radiated noise, use a toroid, pot core or shielded bobbin inductor. See Table 1 for suggested components and Table 2 for a list of component suppliers.
Table 1. Inductor Vendor Information
3443 F06
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SUPPLIER Coilcraft Coiltronics Murata
PHONE (847) 639-6400 (561) 241-7876 USA: (814) 237-1431 (800) 831-9172
FAX (847) 639-1469 (561) 241-9339 USA: (814) 238-0490
WEB SITE www.coilcraft.com www.coiltronics.com www.murata.com
Sumida
USA: www.japanlink.com/ (847) 956-0666 (847) 956-0702 sumida Japan: 81(3) 3607-5111 81(3) 3607-5144
Output Capacitor Selection The bulk value of the capacitor is set to reduce the ripple due to charge into the capacitor each cycle. The steady state ripple due to charge is given by:
%Ripple _ Boost = %Ripple _ Buck = IOUT(MAX) * VOUT - VIN(MIN) * 100 COUT * VOUT * f
2
(
)
% %
IOUT(MAX) * VIN(MAX) - VOUT * 100 COUT * VIN(MAX) * VOUT * f
(
)
where COUT = output filter capacitor, F The output capacitance is usually many times larger in order to handle the transient response of the converter. For a rule of thumb, the ratio of the operating frequency to the unity-gain bandwidth of the converter is the amount the output capacitance will have to increase from the
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LTC3443
APPLICATIO S I FOR ATIO
above calculations in order to maintain the desired transient response. The other component of ripple is due to the ESR (equivalent series resistance) of the output capacitor. Low ESR capacitors should be used to minimize output voltage ripple. For surface mount applications, Taiyo Yuden ceramic capacitors, AVX TPS series tantalum capacitors or Sanyo POSCAP are recommended. Input Capacitor Selection Since the VIN pin is the supply voltage for the IC it is recommended to place at least a 4.7F, low ESR bypass capacitor.
Table 2. Capacitor Vendor Information
SUPPLIER AVX Sanyo PHONE (803) 448-9411 (619) 661-6322 FAX (803) 448-1943 (619) 661-1055 (408) 573-4159 WEB SITE www.avxcorp.com www.sanyovideo.com www.t-yuden.com
Taiyo Yuden (408) 573-4150
Optional Schottky Diodes The Schottky diodes across the synchronous switches B and D are not required (VOUT < 4.3V), but provide a lower drop during the break-before-make time (typically 15ns) of the NMOS to PMOS transition, improving efficiency. Use a Schottky diode such as a Phillips PMEG2010EA or equivalent. Do not use ordinary rectifier diodes, since the slow recovery times will compromise efficiency. For applications with an output voltage above 4.3V, a Schottky diode is required from SW2 to VOUT. Output Voltage < 2.4V The LTC3443 can operate as a buck converter with output voltages as low as 0.4V. The part is specified at 2.4V minimum to allow operation without the requirement of a Schottky diode. Synchronous switch D is powered from VOUT and the RDS(ON) will increase at low output voltages, therefore a Schottky diode is required from SW2 to VOUT to provide the conduction path to the output.
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Output Voltage > 4.3V A Schottky diode from SW to VOUT is required for output voltages over 4.3V. The diode must be located as close to the pins as possible in order to reduce the peak voltage on SW2 due to the parasitic lead and trace inductance. Input Voltage > 4.5V For applications with input voltages above 4.5V which could exhibit an overload or short-circuit condition, a 2/1nF series snubber is required between the SW1 pin and GND. A Schottky diode from SW1 to VIN should also be added as close to the pins as possible. For the higher input voltages, VIN bypassing becomes more critical; therefore, a ceramic bypass capacitor as close to the VIN and GND pins as possible is also required. Operating Frequency Selection Additional quiescent current due to the output switches GATE charge is given by: Buck: 800e-12 * VIN * f Boost: 400e-12 * (VIN + VOUT) * f Buck/Boost: f * (1200e-12 * VIN + 400e-12 * VOUT) where f = switching frequency Closing the Feedback Loop The LTC3443 incorporates voltage mode PWM control. The control to output gain varies with operation region (Buck, Boost, Buck/Boost), but is usually no greater than 15. The output filter exhibits a double pole response is given by:
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fFILTER _ POLE =
1 Hz 2 * * L * COUT
where COUT is the output filter capacitor.
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LTC3443
APPLICATIO S I FOR ATIO
The output filter zero is given by:
fFILTER _ ZERO =
1 2 * * RESR * COUT
Hz
where RESR is the capacitor equivalent series resistance. A troublesome feature in Boost mode is the right-half plane zero (RHP), and is given by:
fRHPZ VIN = Hz 2 * * IOUT * L * VOUT
2
The loop gain is typically rolled off before the RHP zero frequency. A simple Type I compensation network can be incorporated to stabilize the loop but at a cost of reduced bandwidth and slower transient response. To ensure proper phase margin, the loop requires to be crossed over a decade before the LC double pole. The unity-gain frequency of the error amplifier with the Type I compensation is given by: fUG = 1 Hz 2 * * R1 * CP1
Most applications demand an improved transient response to allow a smaller output filter capacitor. To achieve a higher bandwidth, Type III compensation is required. Two zeros are required to compensate for the double-pole response.
U
1 Hz 2 * * 32 e3 * R1 * CP1 Which is extremely close to DC 1 fZERO1 = Hz 2 * * RZ * CP1 1 fZERO2 = Hz 2 * *R1 * CZ 1 fPOLE1 fPOLE2 = 1 Hz 2 * * RZ * CP 2
VOUT
W
UU
+
ERROR AMP
1.22V FB 12 VC 11 CP1 R2
3443 F07
R1
-
Figure 7. Error Amplifier with Type I Compensation
VOUT
+
ERROR AMP
1.22V FB 12 VC 11 CP2
3443 F08
R1
CZ1
-
RZ
CP1
R2
Figure 8. Error Amplifier with Type III Compensation
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LTC3443
TYPICAL APPLICATIO S
Li-Ion to 3.3V at 1.2A Converter
L1 6H 4 9 2.8V TO 4.2V 10 5 8 340k 15k 560pF 200k 220pF D1 VOUT 3.3V 1.2A C2 44F (2 x 22F)
Li-Ion
*1 = Burst Mode OPERATION 0 = FIXED FREQUENCY
EFFICIENCY (%)
14
U
D2
SW1 PVIN VIN
SW2
*
C1 10F
VOUT 12 LTC3443 FB 1 11 VC SHDN/SS 7 2 MODE/SYNC GND 3 6 PGND PGND
2.2k
C1: TAIYO YUDEN JMK212BJ106MG C2: TAIYO YUDEN JMK325BJ226MM D1, D2: PHILLIPS PMEG2010EA L1: SUMIDA CDRH6D28-6R0NC
3443 TA03a
Efficiency vs Load
100 90 80 70 60 50 40 30 20 10 WITH SCHOTTKY DIODES: PHILIPS PMEG2010EA 0 0.1 1 10 100 IOUT (mA) VIN = 2.8V VIN = 4.2V Burst Mode OPERATION VIN = 3.6V
1000
10000
3443 TA03b
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LTC3443
PACKAGE DESCRIPTIO
3.50 0.05 1.70 0.05 2.20 0.05 (2 SIDES) PACKAGE OUTLINE
0.25 0.05 3.30 0.05 (2 SIDES) 0.50 BSC
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 4.00 0.10 (2 SIDES) R = 0.20 TYP 3.00 0.10 (2 SIDES) 1.70 0.10 (2 SIDES) PIN 1 NOTCH
(UE12/DE12) DFN 0603
PIN 1 TOP MARK (NOTE 6)
0.200 REF
BOTTOM VIEW--EXPOSED PAD NOTE: 1. DRAWING PROPOSED TO BE A VARIATION OF VERSION (WGED) 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
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.
U
DE/UE Package 12-Lead Plastic DFN (4mm x 3mm)
(Reference LTC DWG # 05-08-1695)
0.65 0.05 7 R = 0.115 TYP 0.38 0.10 12 0.75 0.05 6 0.25 0.05 3.30 0.10 (2 SIDES) 1 0.50 BSC 0.00 - 0.05
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15
LTC3443 RELATED PARTS
PART NUMBER LT 1613 LT1616 LTC1776 LTC1877 LTC1878 LTC1879 LT1930/LT1930A
(R)
DESCRIPTION 550mA (ISW) 1.4MHz High Efficiency Step-Up DC/DC Converter 500mA (IOUT) 1.4MHz High Efficiency Step-Down DC/DC Converter 500mA (IOUT) 200kHz High Efficiency Step-Down DC/DC Converter 600mA (IOUT) 550kHz Synchronous Step-Down DC/DC Converter 600mA (IOUT) 550kHz Synchronous Step-Down DC/DC Converter 1.2A (IOUT) 550kHz Synchronous Step-Down DC/DC Converter
COMMENTS VIN: 0.9V to 10V, VOUT(MAX) = 34V, IQ = 3mA, ISD 1A, ThinSOTTM High Efficiency, VIN: 3.6V to 25V, VOUT(MIN) = 1.25V, IQ = 1.9mA, ISD 1A, ThinSOT High Efficiency, VIN: 7.4V to 40V, VOUT(MIN) = 1.24V, IQ = 3.2mA, ISD 30A, N8, S8 95% Efficiency, VIN: 2.7V to 10V, VOUT(MIN) = 0.8V, IQ = 10A, ISD 1A, MS8 95% Efficiency, VIN: 2.7V to 6V, VOUT(MIN) = 0.8V, IQ = 10A, ISD 1A, MS8 95% Efficiency, VIN: 2.7V to 10V, VOUT(MIN) = 0.8V, IQ = 15A, ISD 1A, TSSOP16
1A (ISW) 1.2MHz/2.2MHz High Efficiency Step-Up DC/DC Converter VIN 2.6V to 16V, VOUT(MAX) = 34V, IQ = 5.5mA, ISD 1A, ThinSOT 95% Efficiency, VIN: 2.7V to 6V, VOUT(MIN) = 0.8V, IQ = 20A, ISD 1A, ThinSOT 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 20A, ISD 1A, ThinSOT 96% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 40A, ISD 1A, 10-Lead MS 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.8V, IQ = 60A, ISD 1A, 10-Lead MS 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.8V, IQ = 60A, ISD 1A, TSSOP16E 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 2.5V, IQ = 25A, ISD 1A, 10-Lead MS 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 2.5V, IQ = 25A, ISD 1A, DFN
LTC3405/LTC3405A 300mA (IOUT) 1.5MHz Synchronous Step-Down DC/DC Converter LTC3406/LTC3406B 600mA (IOUT) 1.5MHz Synchronous Step-Down DC/DC Converter LTC3407 LTC3411 LTC3412 LTC3440 LTC3441 600mA (IOUT) x2 1.5MHz Dual Synchronous Step-Down DC/DC Converter 1.25A (IOUT) 4MHz Synchronous Step-Down DC/DC Converter 2.5A (IOUT) 4MHz Synchronous Step-Down DC/DC Converter 600mA (IOUT) 2MHz Synchronous Buck-Boost DC/DC Converter High Current Micropower 1MHz Synchronous Buck-Boost DC/DC Converter
ThinSOT is a trademark of Linear Technology Corporation.
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16
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 FAX: (408) 434-0507
LT/TP 0504 1K * PRINTED IN USA
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2004

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