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FEATURES
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LTC3534 7V, 500mA Synchronous Buck-Boost DC/DC Converter DESCRIPTION
The LTC(R)3534 is a wide VIN range, highly efficient, fixed frequency, buck-boost DC/DC converter that operates from input voltages above, below or equal to the output voltage. The topology incorporated in the IC provides a continuous transfer function through all operating modes, making the product ideal for multi-cell Alkaline/NiMH or single Lithium-Ion/Polymer applications where the output voltage is within the battery voltage range. The LTC3534 offers extended VIN and VOUT ranges of 2.4V to 7V and 1.8V to 7V, respectively. Quiescent current is only 25A in Burst Mode operation, maximizing battery life in portable applications. Burst Mode operation is user controlled and can be enabled by driving the PWM pin low. If the PWM pin is driven high then fixed frequency switching is enabled. Other features include fixed 1MHz operating frequency, a <1A shutdown, short-circuit protection, programmable soft-start, current limit and thermal overload protection. The LTC3534 is available in the thermally enhanced 16-lead (3mm x 5mm) DFN and 16-lead GN packages.
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. Burst Mode is a registered trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners.
Regulated Output with Input Voltages Above, Below or Equal to the Output 2.4V to 7V Input and 1.8V to 7V Output Voltage Range 5V VOUT at 500mA from 4 AA Cells Single Inductor Synchronous Rectification: Up to 94% Efficiency Burst Mode(R) Operation with 25A IQ Output Disconnect in Shutdown 1MHz Switching Frequency <1A Shutdown Current Small Thermally Enhanced 16-Lead (5mm x 3mm x 0.75mm) DFN and 16-Lead GN Packages
APPLICATIONS
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Medical Instruments Portable Barcode Readers Portable Inventory Terminals USB to 5V Supply Handheld GPS
TYPICAL APPLICATION
4 AA Cells to 5V at 500mA Buck-Boost Converter
5H 100
4 AA Cells to 5V Efficiency vs VIN
95 SW1 VIN 3.6V TO 6.4V 4 AA CELLS SW2 VOUT 10k LTC3534 FB OFF ON BURST PWM RUN/SS PWM VC 162k
3534 TA01a
+
10F
EFFICIENCY (%)
PVIN VIN
649k
VOUT 5V 22F 500mA
PWM IOUT = 300mA 90 PWM IOUT = 500mA 85
33pF 15k
80
PGND1 GND PGND2 330pF
75 3.6
4.0
4.4
4.8 5.2 VIN (V)
5.6
6.0
6.4
3534 TA01b
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LTC3534 ABSOLUTE MAXIMUM RATINGS
(Note 1)
VIN, PVIN Voltages ........................................ -0.3V to 8V VOUT Voltage ................................................ -0.3V to 8V SW1, SW2 Voltages DC............................................................ -0.3V to 8V Pulsed < 100ns ........................................ -0.3V to 9V RUN/SS, PWM Voltages............................... -0.3V to 8V
VC, FB Voltages ............................................ -0.3V to 6V Operating Temperature Range (Note 2).... -40C to 85C Maximum Junction Temperature (Note 3)............. 125C Storage Temperature Range................... -65C to 150C Lead Temperature (Soldering, 10sec; GN Package) ........................... 300C
PIN CONFIGURATION
TOP VIEW GND RUN/SS GND PGND1 SW1 SW2 PGND2 GND 1 2 3 4 5 6 7 8 17 16 GND 15 FB 14 VC 13 VIN 12 PVIN 11 VOUT 10 PWM 9 GND GND RUN/SS GND PGND1 SW1 SW2 PGND2 GND 1 2 3 4 5 6 7 8 TOP VIEW 16 GND 15 FB 14 VC 13 VIN 12 PVIN 11 VOUT 10 PWM 9 GND
DHC PACKAGE 16-LEAD (5mm x 3mm) PLASTIC DFN TJMAX = 125C, JA = 43C/W (4-LAYER BOARD), JC = 4C/W EXPOSED PAD (PIN 17) IS PGND, MUST BE SOLDERED TO PCB
GN PACKAGE 16-LEAD PLASTIC SSOP NARROW - FUSED TJMAX = 125C,JA = 90C/W (4-LAYER BOARD), JC = 37C/W PINS 1, 8, 9, AND 16 ARE PGND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH LTC3534EDHC#PBF LTC3534EGN#PBF LEAD BASED FINISH LTC3534EDHC LTC3534EGN TAPE AND REEL LTC3534EDHC#TRPBF LTC3534EGN#TRPBF TAPE AND REEL LTC3534EDHC#TR LTC3534EDE#TR PART MARKING 3534 3534 PART MARKING 3534 3534 PACKAGE DESCRIPTION 16-Lead (5mm x 3mm) Plastic DFN 16-Lead SSOP Narrow - Fused PACKAGE DESCRIPTION 16-Lead (5mm x 3mm) Plastic DFN 16-Lead SSOP Narrow - Fused TEMPERATURE RANGE -40C to 85C -40C to 85C TEMPERATURE RANGE -40C to 85C -40C to 85C
Consult LTC Marketing for parts specified with wider operating temperature ranges. 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/
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LTC3534 ELECTRICAL CHARACTERISTICS
PARAMETER Input Start-Up Voltage Input Operating Range Output Voltage Adjust Range Feedback Voltage Feedback Input Current VIN Quiescent Current - Burst Mode Operation VIN Quiescent Current - Shutdown VIN Quiescent Current - Active Input Current Limit Reverse Current Limit Burst Current Limit NMOS Switches Leakage PMOS Switches Leakage PMOS Switches On-Resistance NMOS B Switch On-Resistance NMOS C Switch On-Resistance Maximum Duty Cycle Minimum Duty Cycle Frequency Error Amp AVOL Error Amp Source Current Error Amp Sink Current RUN/SS Threshold RUN/SS Input Current - Shutdown RUN/SS Input Current - Active PWM Threshold PWM Input Current VRUN/SS = 400mV; IC is Shut Down VRUN/SS = 5V; IC is Enabled Measured at PWM Pin; Voltage at which Burst Mode Operation is Disabled (PWMing Enabled) VPWM = 5V 0.4
l
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = VOUT = 5V, unless otherwise noted.
CONDITIONS
l l l
MIN 2.4 1.8 0.975
TYP 2.2
MAX 2.4 7 7
UNITS V V V V nA A A A A mA mA
(Note 4) VFB = Measured Feedback Voltage (Note 4) VFB = 1.2V, VPWM = 0V (Note 5) VRUN/SS = 0V, Not Including Switch Leakage, VOUT = 0V VFB = 1.2V, VPWM = 5V (Note 5) VPWM = 5V VPWM = 5V VPWM = 0V Switches B and C Switches A and D Switches A and D Switch B Switch C Boost (% Switch C On) Buck (% Switch A On)
l
1 1 25 0.1 420
1.015 50 50 1 700
l
1
1.8 500 400 0.1 0.1 260 275 215 7 10
A A m m m % %
l l l l
75 100 0.80
85 0 1 74 -15 225 1.15
% MHz dB A A
(Note 4)
0.4
1 0.02 0.28 1 1.25
1.4 1 1 1.4 2.5
V A A V 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 LTC3534E 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: 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. Note 4: The IC is tested in a feedback loop to make this measurement. Note 5: Current Measurements are performed when the outputs are not switching.
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LTC3534 TYPICAL PERFORMANCE CHARACTERISTICS
4 Alkaline Cells to 5V Efficiency vs ILOAD
100 Burst 90 Mode OPERATION 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0.01 0.1 VIN = 3.6V VIN = 5V VIN = 6.4V 1 10 100 LOAD CURRENT (mA) 1000
3534 G01
TA = 25C, unless otherwise noted.
USB to 5V Efficiency vs ILOAD
100 Burst 90 Mode OPERATION 80 70 60 50 40 30 20 10 0.01 0.1 VIN = 4.35V VIN = 4.8V VIN = 5.25V 1 10 100 LOAD CURRENT (mA) 1000
3534 G02
EFFICIENCY (%)
Active Quiescent and Burst Mode SLEEP Currents vs VIN
425 ACTIVE QUIESCENT CURRENT (A) VFB = 1.2V ACTIVE QUIESCENT CURRENT 415 28 30 Burst Mode SLEEP CURRENT (A) 3.3 3.0 CURRENT LIMIT (A) 2.7 2.4 2.1
Current Limits vs VIN
VOUT = 5V
PEAK CURRENT LIMIT
405
26
395
Burst Mode SLEEP CURRENT
24
LINEAR CURRENT LIMIT 1.8 1.5 2.4
385 2.4
3.2
4.8 5.6 6.4 4 INPUT VOLTAGE (V)
7.2
8
22
3.2
4.8 5.6 6.4 4 INPUT VOLTAGE (V)
7.2
8
3534 G03
3534 G04
Minimum Start-Up Voltage vs Temperature
2.200 ACTIVE QUIESCENT CURRENT (A) 450
Active Quiescent Current vs Temperature
VFB = 1.2V Burst Mode SLEEP CURRENT (A) 50
Burst Mode SLEEP Current vs Temperature
VFB = 1.2V
VIN START VOLTAGE (V)
430
40
2.175
410
30
2.150
390
20
2.125 -50
-25
0 50 25 TEMPERATURE (C)
75
100
3534 G05
370 -50
-25
0 50 25 TEMPERATURE (C)
75
100
3534 G06
10 -50
-25
0 50 25 TEMPERATURE (C)
75
100
3534 G07
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LTC3534 TYPICAL PERFORMANCE CHARACTERISTICS
Converter Line Regulation vs Temperature
5.005 CONVERTER LINE REGULATION (V) 5.000 4.995 4.990 4.985 4.980 4.975 -50 3.6V 5.0V 6.4V -25 0 50 25 TEMPERATURE (C) 75 100
3534 G08
TA = 25C, unless otherwise noted.
Converter Load Regulation vs Temperature
5.01 CONVERTER LOAD REGULATION (V) 5.00 1.000 FB VOLTAGE (V) 4.99 4.98 500mA 4.97 4.96 4.95 -50 300mA VIN = 5V 1.001 25mA
Feedback Voltage vs Temperature
ILOAD = 100mA
0.999
0.998
-25
0 50 25 TEMPERATURE (C)
75
100
3534 G09
0.997 -50
-25
0 50 25 TEMPERATURE (C)
75
100
3534 G10
Switching Frequency vs Temperature
1050 3.0 2.8 1025 CURRENT LIMIT (A) 2.5 2.3 2.0
Current Limits vs Temperature
BURST NO-LOAD INPUT CURRENT (A) VIN = VOUT = 5V 50
BURST No-Load Input Current vs VIN (Switching)
VOUT = 5V
SWITCHING FREQUENCY (kHz)
PEAK CURRENT LIMIT
45
1000
40
975 1.8 950 -50 1.5 -50
LINEAR CURRENT LIMIT
35
-25
0 50 25 TEMPERATURE (C)
75
100
3534 G11
-25
25 0 50 TEMPERATURE (C)
75
100
3534 G12
30 2.4
3.2
4 4.8 5.6 6.4 INPUT VOLTAGE (V)
7.2
8
3534 G13
PWM No-Load Input Current vs VIN (Switching)
18 PWM NO-LOAD INPUT CURRENT (mA) VOUT = 5V OUTPUT CURRENT CAPABILITY (mA) 225 200 175 150 125 100 75
BURST Maximum Output Current Capability vs VIN
1800 OUTPUT CURRENT CAPABILITY (mA)
PWM Maximum Output Current Capability vs VIN
VOUT = 5V 1600 L = 4.7H 1400 1200 1000 800 600 400 200 2.4 3.2 4.8 5.6 6.4 4 INPUT VOLTAGE (V) 7.2 8
14
10
6
2 2.4
3.2
4.8 5.6 6.4 4 INPUT VOLTAGE (V)
7.2
8
50 2.4
VOUT = 5V Burst Mode OPERATION 3.2 4 4.8 5.6 6.4 INPUT VOLTAGE (V) 7.2 8
3534 G14
3534 G15
3534 G16
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LTC3534 TYPICAL PERFORMANCE CHARACTERISTICS
VOUT Ripple at 300mA Load
VIN = 5V VIN = 3.6V VIN = 6.4V ILOAD = 100mA/DIV 1s/DIV VOUT = 5V, AC-COUPLED 20mV/DIV COUT = 22F ILOAD = 300mA
3534 G17 3534 G18
TA = 25C, unless otherwise noted. Load Transient Response in Fixed Frequency Mode, No-Load to 300mA
VOUT = 100mV/DIV
100s/DIV VIN = VOUT = 5V ILOAD = 0 TO 300mA COUT = 22F X5R CERAMIC
Burst Mode Operation VOUT Ripple at 25mA Load
VOUT = 50mV/DIV VOUT = 50mV/DIV
Transition from Burst Mode Operation to Fixed Frequency Mode
INDUCTOR CURRENT = 200mA/DIV 10s/DIV VIN = VOUT = 5V COUT = 22F X5R CERAMIC
3534 G19
PWM = 2V/DIV 100s/DIV VIN = VOUT = 5V ILOAD = 25mA COUT = 22F X5R CERAMIC
3534 G20
VOUT Start-Up
VOUT = 2V/DIV RUN/SS = 1V/DIV (STARTS AT 1V) INDUCTOR CURRENT = 500mA/DIV 500s/DIV ILOAD = 100mA
3534 G21
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LTC3534 PIN FUNCTIONS
GND Pads (Pins 1, 8, 9, 16; GN Package): IC Substrate Grounds. These pins MUST be soldered to the printed circuit board ground to provide both electrical contact and a good thermal contact to the PCB. RUN/SS (Pin 2): Combined Shutdown and Soft-Start. Applying a voltage below 400mV shuts down the IC. Apply a voltage above 1.4V to enable the IC and above 2.4V to ensure that the error amp is not clamped from soft-start. An R-C from the enable command signal to this pin will provide a soft-start function by limiting the rise time of the VC pin. GND (Pin 3): Signal Ground for the IC. PGND1, PGND2 (Pins 4, 7): Power Ground for the Internal N-channel MOSFET Power Switches (Switches B and C). SW1 (Pin 5): Switch Pin where Internal Switches A and B are Connected. Connect inductor from SW1 to SW2. Minimize trace length to reduce EMI. SW2 (Pin 6): Switch Pin where Internal Switches C and D are Connected. Minimize trace length to reduce EMI. PWM (Pin 10): Burst Mode Select. Applying a voltage below 400mV enables Burst Mode operation, providing a significant efficiency improvement at light loads. During the period where the IC is supplying energy to the output, the inductor peak current will reach 400mA typical and return to zero current on each cycle. Burst Mode operation will continue until this pin is driven high. Applying a voltage above 1.4V disables Burst Mode operation, enabling low noise, fixed frequency operation. VOUT (Pin 11): 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. VOUT is given by the following equation: VOUT = 1.000 * R1+ R2 V R2
PVIN (Pin 12): Power VIN Supply Pin. A 10F ceramic capacitor is recommended as close to the PVIN and PGND pins as possible. VIN (Pin 13): Input Supply Pin. Connect the power source to this pin. VC (Pin 14): Error Amp Output. An R-C network is connected from this pin to FB for loop compensation. Refer to "Closing the Feedback Loop" section for component selection guidelines. FB (Pin 15): Feedback Pin. Connect VOUT resistor divider tap to this pin. The output voltage can be adjusted from 1.8V to 7V. The feedback reference voltage is typically 1V. Exposed Pad (Pin 17; DHC Package): IC Substrate Ground. This pin MUST be soldered to the printed circuit board ground to provide both electrical contact and a good thermal contact to the PCB.
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LTC3534 BLOCK DIAGRAM
L1 5 ANTIRING 6 SW1 12 PVIN SW A SW2 SW D VOUT 11 COUT 13 CIN VIN SW B PGND1 GATE DRIVERS AND ANTICROSS CONDUCTION -500mA VOUT 1.8V TO 7V
VIN 2.4V TO 7V
PGND2
+
Gm = 1 100k 1.8A FB AVERAGE CURRENT LIMIT THERMAL SHUTDOWN VREF 1V 2.6A 15
-
+ -
SUPPLY CURRENT LIMIT
+
2.2V
+
UVLO PWM LOGIC AND OUTPUT PHASING
ERROR AMP
-
-
PWM COMPARATORS VC RZ CP1 14 CP2
SHUTDOWN RSS 2 CSS RUN/SS SHUTDOWN AND SOFT-START
1MHz OSC SLEEP Burst Mode OPERATION PWM 10 CONTROL PGND2 7
PGND1 4
GND 3
EXPOSED PAD 17
8
+
-
+
REVERSE CURRENT LIMIT RFF CZ1
- - +
+ + + +
SW C
R1
R2
3534 BD
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LTC3534 OPERATION
The LTC3534 provides high efficiency, low noise power for a wide variety of handheld electronic devices. Linear Technology's proprietary topology allows input voltages above, below or equal to the output voltage by properly phasing the output switches. The error amplifier output voltage on VC determines the output duty cycle of the switches. Since VC 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. High efficiency is achieved at light loads when Burst Mode operation is invoked and the LTC3534's quiescent current drops to a mere 25A. LOW NOISE FIXED FREQUENCY OPERATION Oscillator The frequency of operation is internally set to 1MHz. Error Amplifier The error amplifier is a voltage mode amplifier. The loop compensation components are configured around the amplifier (from FB to VC) to obtain stability of the converter. For improved bandwidth, an additional R-C feedforward network can be placed across the upper feedback divider resistor. The voltage on RUN/SS clamps the error amplifier output, VC, to provide a soft-start function. Supply Current Limits There are two different supply current limit circuits in the LTC3534, each having internally fixed thresholds.
PVIN 12 PMOS A SW1 5 NMOS B 4 PGND1 7 L1 SW2 6 NMOS C 0%
3534 F01 3534 F02
The first circuit is an average current limit amplifier, sourcing current out of FB to drop the output voltage should the peak input current exceed 1.8A typical. This method provides a closed loop means of clamping the input current. During conditions where VOUT is near ground, such as during a short circuit or start-up, this threshold is cut to 800mA typical, providing a foldback feature. For this current limit feature to be most effective, the Thevenin resistance from FB to ground should be greater than 100k. Should the peak input current exceed 2.6A typical, the second circuit, a high speed peak current limit comparator, shuts off PMOS switch A. The delay to output of this comparator is typically 50ns. Reverse Current Limit During fixed frequency operation, the LTC3534 operates in forced continuous conduction mode. The reverse current limit comparator monitors the inductor current from the output through PMOS switch D. Should this negative inductor current exceed 500mA typical, the LTC3534 shuts off switch D. Four-Switch Control Figure 1 shows a simplified diagram of how the four internal switches are connected to the inductor, PVIN, VOUT, PGND1 and PGND2. Figure 2 shows the regions of operation for the LTC3534 as a function of the internal control voltage, VCI. Dependent on the magnitude of VCI, the LTC3534 will operate in buck, buck-boost or boost mode. VCI is a level
DUTY CYCLE 85% DMAX BOOST INTERNAL CONTROL VOLTAGE, VCI V4 ( 1.2V) A ON, B OFF PWM C AND D SWITCHES FOUR SWITCH PWM D ON, C OFF PWM A AND B SWITCHES BOOST REGION V3 ( 720mV) BUCK-BOOST REGION V2 ( 640mV) BUCK REGION V1 ( 100mV)
VOUT 11 PMOS D
DMIN BOOST DMAX BUCK
PGND2
Figure 1. Simplified Diagram of Output Switches
Figure 2. Switch Control vs Internal Control Voltage, VCI
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LTC3534 OPERATION
shifted voltage from the output of the error amplifier (VC pin), see Figure 3. The four power switches are properly phased so the transfer between operating modes is continuous, smooth and transparent to the user. When VIN approaches VOUT the buck-boost region is entered, where the conduction time of the four switch region is typically 125ns. 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 period. Switches A and B will alternate 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 = (125ns * f) * 100% where f = operating frequency in Hz, typically 1MHz. Hence, D4SW = 12.5% for the LTC3534. DMAX_BUCK = 87.5% 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 VCI 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- (125ns * f ) The VIN potential at which the four switch region ends is given by: VIN = VOUT * (1 - D) = VOUT * (1 - 125ns * ) V where f = operating frequency in Hz, typically 1MHz. Hence, for the LTC3534, VIN(ENTER4SW) VOUT V 0.875
Approximate VIN potential at which the four switch region is entered. VIN(4SWEXIT) 0.875 * VOUT V Approximate VIN potential at which the four switch region is exited. 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 85% typical and is reached when VCI is above V4. Burst Mode OPERATION Burst Mode operation reduces the LTC3534's quiescent current consumption at light loads and improves overall conversion efficiency, increasing battery life. During Burst Mode operation the LTC3534 delivers energy to the output until it is regulated and then enters a sleep state where the switches are off and the quiescent current drops to 25A typical. In this mode the output ripple has a variable frequency component that depends upon load current, and will typically be about 2% peak-to-peak. Burst Mode operation ripple can be reduced slightly by using more output capacitance (47F or greater). Another method of reducing Burst Mode operation ripple is to place a small feedforward capacitor across the upper resistor in the VOUT feedback divider network (as in Type III compensation), see Figure 6.
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LTC3534 OPERATION
In Burst Mode operation the typical maximum average output currents in the three operating regions, buck, four switch, and boost are given by: IOUT(MAX)BURST-BUCK 100mA; Burst Mode operation - buck region: VIN > VOUT IOUT(MAX)BURST-FOUR_SWITCH 200mA; Burst Mode operation - four switch region: VIN VOUT IOUT(MAX)BURST -BOOST 200 * VIN mA; VOUT Burst Mode Operation to Fixed Frequency Transient Response In Burst Mode operation, the compensation network is not used and VC is disconnected from the error amplifier. During long periods of Burst Mode operation, leakage currents in the external components or on the PC board could cause the compensation capacitor to charge (or discharge), which could result in a large output transient when returning to fixed frequency mode operation, even at the same load current. To prevent this, the LTC3534 incorporates an active clamp circuit that holds the voltage on VC at an optimal voltage during Burst Mode operation. This minimizes any output transient when returning to fixed frequency mode operation. For optimum transient response, Type III compensation is also recommended to broad band the control loop and roll off past the two pole response of the output LC filter. (See Closing the Feedback Loop). Soft-Start The soft-start function is combined with shutdown. When the RUN/SS pin is brought above 1V typical, the LTC3534 is enabled but the error amplifier duty cycle is clamped from VC. A detailed diagram of this function is shown in Figure 3. The components RSS and CSS provide a slow ramping voltage on RUN/SS to provide a soft-start function. To ensure that VC is not being clamped, RUN/SS must be raised to 2.4V or above.
Burst Mode operation - boost region: VIN < VOUT The efficiency below 1mA becomes dominated primarily by the quiescent current. The Burst Mode operation efficiency is given by: Efficiency *ILOAD 25A +ILOAD
where is typically 90% during Burst Mode operation. A graph of Burst Mode operation maximum output current vs VIN (for VOUT = 5V) is provided in the Typical Performance Characteristics section.
VIN 13 RSS RUN/SS 2 CSS ERROR AMP VOUT
ENABLE SIGNAL
+ -
1V FB 15 VC CP1
11 R1
R2
3534 F03
CHIP ENABLE
+ -
1V
VCI
14 TO PWM COMPARATORS
Figure 3. Soft-Start Circuitry
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LTC3534 APPLICATIONS INFORMATION
COMPONENT SELECTION
2 RUN/SS 3 GND 4 PGND1 5 SW1 6 SW2 7 PGND2
FB 15 VC 14 VIN 13 VIN PVIN 12 VOUT 11 PWM 10 MULTIPLE VIAS
3534 F04
VOUT PWM
Figure 4. 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. Keep VOUT and VIN Ceramic Capacitors Close to their IC Pins.
Inductor Selection The high frequency operation of the LTC3534 allows the use of small surface mount inductors. The inductor ripple current is typically set to 20% to 40% of the maximum inductor current. For a given ripple the inductance terms are given as follows: LBOOST > LBUCK > VIN(MIN) * VOUT - VIN(MIN) f * IL * VOUT
IL = maximum allowable inductor ripple current, A VIN(MIN) = minimum input voltage, V VIN(MAX) = maximum input voltage, V VOUT = output voltage, V For high efficiency, choose a ferrite inductor with a high frequency core material 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 shielded inductor. See Table 1 for a suggested list of inductor suppliers.
WEBSITE www.coilcraft.com www.fdk.com www.murata.com
(
)H
VOUT * VIN(MAX) - VOUT f * IL * VIN(MAX)
(
)H
where f = switching frequency in Hz, typically 1MHz.
Table 1. Inductor Vendor Information
SUPPLIER Coilcraft FDK Murata Sumida TDK TOKO PHONE (847) 639-6400 (408) 432-8331 (814) 237-1431 (800) 831-9172
FAX OR E-MAIL (847) 639-1469 america@fdk.com (814) 238-0490
USA: (847) 956-0666 USA: (847) 956-0702 www.sumida.com Japan: 81(3) 3607-5111 Japan: 81(3) 3607-5144 (847) 803-6100 (847) 297-0070 (847) 803-6296 (847) 699-7864 www.component.tdk.com www.tokoam.com
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LTC3534 APPLICATIONS INFORMATION
Output Capacitor Selection The bulk value of the output filter 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:
VP-P Boost = VP-P Buck = IOUT * VOUT - VIN(MIN) COUT * VOUT * f 1 8 * L * COUT * f * 2
Input Capacitor Selection Since VIN is the supply voltage for the IC, as well as the input to the power stage of the converter, it is recommended to place at least a 10F low ESR ceramic bypass , capacitor close to the PVIN/VIN and PGND/GND pins. It is also important to minimize any stray resistance from the converter to the battery or other power source. Optional Schottky Diodes Schottky diodes across the synchronous switches B and D are not required, but do provide a lower drop during the break-before-make time (typically 15ns), thus improving efficiency. Use a surface mount Schottky diode such as an MBRM120T3 or equivalent. Do not use ordinary rectifier diodes since their slow recovery times will compromise efficiency. Output Voltage < 1.8V The LTC3534 can operate as a buck converter with output voltages as low as 400mV. Since synchronous switch D is powered from VOUT and the RDS(ON) will increase significantly at output voltages below 1.8V typical, a Schottky diode is required from SW2 to VOUT to provide the conduction path to the output at low VOUT voltages. The current limit is folded back to 800mA when VOUT < 0.9V typical which will significantly reduce the output current capability of the application. Note that Burst Mode operation is inhibited at output voltages below 1.6V typical. Closing the Feedback Loop The LTC3534 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, as given by:
fFILTER _ POLE = fFILTER _ POLE = 1 Hz (in buck mode) 2 * * L1* COUT VIN 2 * VOUT * * L1* COUT Hz (in boost mode)
(
)V
- VOUT * VOUT VIN(MAX)
(V
IN(MAX)
)
V
where f = switching frequency in Hz, typically 1MHz. COUT = output filter capacitor, F IOUT = output load current, A The output capacitance is usually many times larger than the minimum value in order to handle the transient response requirements of the converter. As 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 above calculations in order to maintain the desired transient response. A 22F or larger ceramic capacitor is appropriate for most applications. 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 or TDK ceramic capacitors, AVX TPS series tantalum capacitors or Sanyo POSCAP are recommended. See Table 2 for contact information.
Table 2. Capacitor Vendor Information
SUPPLIER PHONE AVX Sanyo Taiyo Yuden TDK FAX WEBSITE (803) 448-9411 (803) 448-1943 www.avxcorp.com (619) 661-6322 (619) 661-1055 www.sanyovideo.com (408) 573-4150 (408) 573-4159 www.t-yuden.com (847) 803-6100 (847) 803-6296 www.component.tdk.com
where L1 is in Henries and COUT is in Farads.
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13
LTC3534 APPLICATIONS INFORMATION
The output filter zero is given by: fFILTER _ ZERO = 1 2 * * RESR * COUT Hz Most applications demand an improved transient response to allow a smaller output filter capacitor. To achieve a higher bandwidth, Type III compensation is required, providing two zeros to compensate for the double-pole response of the output filter. Referring to Figure 6, the location of the poles and zeros are given by: 2 * * 5 x 103 * R1* CP1 (which is extremely close to DC) f ZERO1 = 1 Hz 2 * * R Z * CP1 1 f ZERO2 = Hz 2 * * R1* CZ1 1 Hz fPOLE2 = 2 * * R Z * CP2 fPOLE1 1 Hz
where RESR is the equivalent series resistance of the output capacitor. A troublesome feature in boost mode is the right-half plane zero (RHP), given by: VIN 2 fRHPZ = Hz 2 * *IOUT * L1* VOUT 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 using Type I compensation, the loop must be crossed over a decade before the LC double pole. Referring to Figure 5, the unity-gain frequency of the error amplifier utilizing Type I compensation is given by: fUG = 1 Hz 2 * * R1* CP1
where resistance is in Ohms and capacitance is in Farads.
VOUT VOUT
+
ERROR AMP
1V FB 15 VC RZ CP2
11 CZ1 R1
+
ERROR AMP
1V FB 15 VC 14 CP1
11 R1
-
-
CP1
R2
14 R2
3534 F05 3534 F06
Figure 5. Error Amplifier with Type I Compensation
Figure 6. Error Amplifier with Type III Compensation
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14
LTC3534 TYPICAL APPLICATIONS
4 Alkaline/NiMH to 5V at 500mA
L1 5H
SW1 VIN 3.6V TO 6.4V 4 ALKALINE/ NiMH CELLS
SW2 VOUT LTC3534 RFF 10k CZ1 33pF FB CP1 330pF RZ 15k VC COUT 22F
+
CIN RSS 200k 10F
PVIN VIN
VOUT 5V 500mA R1 649k
RUN/SS CSS 0.056F BURST PWM PWM
CP2 10pF R2 162k
3534 TA02a
PGND1 GND PGND2 L1: COILCRAFT MSS7341
4 Alkaline/NiMH Cells to 5V Efficiency vs ILOAD
100 Burst 90 Mode OPERATION 80 70 60 50 40 30 20 10 0.01 0.1 VIN = 3.6V VIN = 5V VIN = 6.4V 1 10 100 LOAD CURRENT (mA) 1000
3534 TA02b
EFFICIENCY (%)
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15
LTC3534 TYPICAL APPLICATIONS
USB to 5V at 500mA
L1 5H
SW1 USB 4.35V TO 5.25V RSS CIN 200k 10F PVIN VIN LTC3534 RUN/SS CSS 0.056F
SW2 VOUT RFF 10k CZ1 33pF FB CP1 330pF RZ 15k VC COUT 22F
VOUT 5V 500mA* R1 649k
BURST PWM
PWM
CP2 10pF R2 162k
3534 TA03a
PGND1 GND PGND2 L1: COILCRAFT MSS7341
*NOTE: OUTPUT CURRENT CAN BE LESS THAN 500mA IF USB INPUT CURRENT LIMIT REACHED.
USB to 5V Efficiency vs ILOAD
100 Burst 90 Mode OPERATION 80 70 60 50 40 30 20 10 0.01 0.1 VIN = 4.35V VIN = 4.8V VIN = 5.25V 1 10 100 LOAD CURRENT (mA) 1000
3534 TA03b
EFFICIENCY (%)
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16
LTC3534 TYPICAL APPLICATIONS
Li-Ion to 3.3V at 400mA
L1 3.3H
SW1 VIN 2.7V TO 4.2V 1 Li-Ion CELL
SW2 VOUT LTC3534 RFF 10k CZ1 66pF CP1 470pF RZ 15k VC COUT 22F
+
RSS 200k
CIN 10F
PVIN VIN
VOUT 3.3V 400mA R1 374k
RUN/SS CSS 0.056F BURST PWM PWM
FB
CP2 10pF R2 162k
3534 TA04a
PGND1 GND PGND2 L1: TDK RLF7030
Li-Ion to 3.3V Efficiency vs ILOAD
100 Burst 90 Mode OPERATION 80 70 60 50 40 30 20 10 0.01 0.1 VIN = 2.7V VIN = 3.6V VIN = 4.2V 1 10 100 LOAD CURRENT (mA) 1000
3534 TA04b
EFFICIENCY (%)
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17
LTC3534 PACKAGE DESCRIPTION
DHC Package 16-Lead Plastic DFN (5mm x 3mm)
(Reference LTC DWG # 05-08-1706)
0.65 0.05 3.50 0.05
1.65 0.05 2.20 0.05 (2 SIDES) PACKAGE OUTLINE 0.25 0.05 0.50 BSC 4.40 0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 5.00 0.10 (2 SIDES) R = 0.20 TYP 3.00 0.10 (2 SIDES) PIN 1 TOP MARK (SEE NOTE 6) 8 0.200 REF 0.75 0.05 4.40 0.10 (2 SIDES) BOTTOM VIEW--EXPOSED PAD NOTE: 1. DRAWING PROPOSED TO BE MADE VARIATION OF VERSION (WJED-1) 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 1 0.25 0.05 0.50 BSC 1.65 0.10 (2 SIDES) PIN 1 NOTCH
(DHC16) DFN 1103
R = 0.115 TYP 9 16
0.40 0.10
0.00 - 0.05
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18
LTC3534 PACKAGE DESCRIPTION
GN Package 16-Lead Plastic SSOP (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1641)
.045 .005 .189 - .196* (4.801 - 4.978) 16 15 14 13 12 11 10 9
.009 (0.229) REF
.254 MIN
.150 - .165 .229 - .244 (5.817 - 6.198) .150 - .157** (3.810 - 3.988)
.0165 .0015
.0250 BSC 1 .015 .004 (0.38 0.10)
45
RECOMMENDED SOLDER PAD LAYOUT 23 4 56 7 8 .004 - .0098 (0.102 - 0.249)
.0532 - .0688 (1.35 - 1.75)
.007 - .0098 (0.178 - 0.249)
0 - 8 TYP
.016 - .050 (0.406 - 1.270) NOTE: 1. CONTROLLING DIMENSION: INCHES INCHES 2. DIMENSIONS ARE IN (MILLIMETERS) 3. DRAWING NOT TO SCALE *DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
.008 - .012 (0.203 - 0.305) TYP
.0250 (0.635) BSC
GN16 (SSOP) 0204
3534f
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.
19
LTC3534 RELATED PARTS
PART NUMBER LTC3125 DESCRIPTION 1.2A (ISW), 1.5MHz, Synchronous Step-Up DC/DC Converter with Programmable Input Current 3A (ISW), 3MHz, Synchronous Step-Up DC/DC Converter with Output Disconnect 1.5A (ISW), 3MHz, Synchronous Step-Up DC/DC Converter with Output Disconnect 5A (ISW), 8MHz (Low Ripple), 4-Phase Synchronous Step-Up DC/DC Converter with Output Disconnect 600mA (ISW), 500KHz, Synchronous Step-Up DC/DC Converter with Output Disconnect and Soft-Start 600mA (IOUT), 2MHz, Synchronous Buck-Boost DC/DC Converter 1.2A (IOUT), 1MHz/600kHz, Synchronous Buck-Boost DC/DC Converter 1.2A (IOUT), 2MHz, Synchronous Buck-Boost DC/DC Converter 400mA (IOUT), 1.5MHz, Synchronous Buck-Boost DC/DC Converter with wide VOUT Range 1A (IOUT), 2MHz Synchronous Buck-Boost, 600mA Buck DC/DC Converter Synchronous 400mA (IOUT) Buck-Boost and 200mA (IOUT) Buck, 1MHz, DC/DC Converters 500mA (IOUT), 1MHz Synchronous Step-Up DC/DC Converter with Output Disconnect COMMENTS 93% Efficiency, VIN: 1.8V to 5V, VOUT(MAX) = 5.25V, IQ = 15A, ISD < 1A, 5% Input Current Accuracy, 200mA to 1A Program Range, 2mm x 3mm DFN Package 96% Efficiency, VIN: 0.5V to 4.5V, VOUT(MAX) = 5.25V, IQ = 12A, ISD <1A, QFN24 Package 96% Efficiency, VIN: 0.5V to 4.5V, VOUT(MAX) = 5.25V, IQ = 25A, ISD <1A, DFN10 Package 95% Efficiency, VIN: 0.5V to 4.5V, VOUT(MAX) = 5.25V, IQ = 12A, ISD <1A, QFN32 Package 96% Efficiency, VIN: 0.5V to 4.4V, VOUT(MAX) = 5V, IQ = 20A, ISD <1A, ThinSOT-23 Package 96% Efficiency, VIN: 2.5V to 5.5V, VOUT(MAX) = 5.5V, IQ = 25A, ISD <1A, MSOP and DFN Packages 95%/96% Efficiency, VIN: 2.4V to 5.5V, VOUT(MAX) = 5.25V, IQ = 35A/28A, ISD <1A, MSOP Packages 95% Efficiency, VIN: 2.4V to 5.5V, VOUT(MAX) = 5.25V, IQ = 25A, ISD <1A, DFN Package 93% Efficiency, VIN: 2.7V to 5.5V, VOUT: 0.5V to 5V, ISD <1A, DFN Package, Ideal for WCDMA PA Bias 95% Efficiency, VIN: 2.2V to 5.5V, VOUT(MAX) = 5.25V, VOUT(MIN) = 0.8V; IQ = 55A, ISD < 1A, QFN Package 95% Efficiency, VIN: 2.4V to 5.5V, VOUT(MAX) = 5.25V, VOUT(MIN) = 0.6V; IQ = 25A, ISD <1A, QFN Package 94% Efficiency, VIN: 0.8V to 5V, VOUT(MAX) = 5.25V, IQ = 9A, ISD <1A, 2mm x 2mm DFN-6 Package
LTC3421 LTC3422 LTC3425 LTC3429 LTC3440 LTC3441/LTC3443 LTC3442 LTC3444 LTC3520 LTC3522 LTC3526L LTC3530 LTC3531
600mA (IOUT), 2MHz, Synchronous Buck-Boost DC/DC 96% Efficiency, VIN: 1.8V to 5.5V, VOUT(MAX) = 5.25V, Converter with Wide Input Voltage Range IQ = 40A, ISD <1A, MSOP and DFN Packages 200mA (IOUT), Burst Mode Operation, Synchronous Buck-Boost DC/DC Converter with Adjustable and Fixed VOUT Versions 500mA (IOUT), 2MHz, Synchronous Buck-Boost DC/DC Converter 2A (IOUT), 2MHz, Synchronous Buck-Boost DC/DC Converter with Wide Input Voltage Range 800mA (IOUT), 1MHz, Synchronous Buck-Boost DC/DC Converter 90% Efficiency, VIN: 1.8V to 5.5V, VOUT(MAX) = 5V, IQ = 16A Always since Burst Mode Operation, ISD <1A, Small ThinSOT and DFN Packages 95% Efficiency, VIN: 2.4V to 5.5V, VOUT(MAX) = 5.25V, IQ = 35A, ISD <1A, MSOP and DFN Packages 96% Efficiency, VIN: 1.8V to 5.5V, VOUT(MAX) = 5.25V, IQ = 40A, ISD <1A, MSOP and DFN Packages 95% Efficiency, VIN: 2.4V to 5.5V, VOUT(MAX) = 5.25V, IQ = 35A, ISD = 1.5A, DFN Package
LTC3532 LTC3533 LTC3538
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20 Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
LT 0209 * PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2009

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