LTC3534 7V, 500mA Synchronous Buck-Boost DC/DC Converter Description Features n n n n n n n n n n Regulated Output with Input Voltages Above, Below or Equal to the Output 2.4V to 7V VIN and 1.8V to 7V VOUT Ranges 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 n n n n n Medical Instruments Portable Barcode Readers Portable Inventory Terminals USB to 5V Supply Handheld GPS 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. Typical Application 4 AA Cells to 5V at 500mA Buck-Boost Converter 4 AA Cells to 5V Efficiency vs VIN 100 5H 4 AA CELLS + 10F OFF ON BURST PWM SW2 PVIN VIN VOUT 95 10k LTC3534 RUN/SS PWM 649k 33pF FB 15k VOUT 5V 22F 500mA PWM IOUT = 300mA EFFICIENCY (%) VIN 3.6V TO 6.4V SW1 VC PGND1 GND PGND2 330pF 90 PWM IOUT = 500mA 85 80 162k 3534 TA01a 75 3.6 4.0 4.4 4.8 5.2 VIN (V) 5.6 6.0 6.4 3534 TA01b 3534fb For more information www.linear.com/LTC3534 1 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 1 TOP VIEW GND 1 16 GND RUN/SS 2 15 FB 16 GND RUN/SS 2 15 FB GND 3 14 VC GND 3 14 VC PGND1 4 13 VIN PGND1 4 13 VIN SW1 5 12 PVIN SW1 5 12 PVIN 6 11 VOUT 17 SW2 6 11 VOUT SW2 PGND2 7 10 PWM PGND2 7 10 PWM GND 8 9 GND 8 9 GND GND GN PACKAGE 16-LEAD PLASTIC SSOP NARROW - FUSED 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 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 TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LTC3534EDHC#PBF LTC3534EDHC#TRPBF 3534 16-Lead (5mm x 3mm) Plastic DFN -40C to 85C LTC3534EGN#PBF LTC3534EGN#TRPBF 3534 16-Lead SSOP Narrow - Fused -40C to 85C LEAD BASED FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LTC3534EDHC LTC3534EDHC#TR 3534 16-Lead (5mm x 3mm) Plastic DFN -40C to 85C LTC3534EGN LTC3534EDE#TR 3534 16-Lead SSOP Narrow - Fused -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/ 3534fb 2 For more information www.linear.com/LTC3534 LTC3534 Electrical Characteristics 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. PARAMETER CONDITIONS MIN TYP MAX 2.2 UNITS Input Start-Up Voltage l 2.4 V Input Operating Range l 2.4 7 V Output Voltage Adjust Range l 1.8 7 V l 0.975 1 1.015 V Feedback Voltage (Note 4) Feedback Input Current VFB = Measured Feedback Voltage (Note 4) 1 50 nA VIN Quiescent Current - Burst Mode Operation VFB = 1.2V, VPWM = 0V (Note 5) 25 50 A VIN Quiescent Current - Shutdown VRUN/SS = 0V, Not Including Switch Leakage, VOUT = 0V 0.1 1 A VIN Quiescent Current - Active VFB = 1.2V, VPWM = 5V (Note 5) 420 700 A Input Current Limit VPWM = 5V Reverse Current Limit Burst Current Limit 1.8 A VPWM = 5V 500 mA VPWM = 0V 400 mA l 1 NMOS Switches Leakage Switches B and C 0.1 7 A PMOS Switches Leakage Switches A and D 0.1 10 A PMOS Switches On-Resistance Switches A and D 260 m NMOS B Switch On-Resistance Switch B 275 m NMOS C Switch On-Resistance Switch C 215 m Maximum Duty Cycle Boost (% Switch C On) Buck (% Switch A On) 85 % % l l Minimum Duty Cycle l Frequency l 75 100 0 0.80 1 1.15 MHz 74 dB Error Amp Source Current -15 A Error Amp Sink Current 225 A Error Amp AVOL (Note 4) % RUN/SS Threshold l 0.4 1 1.4 V RUN/SS Input Current - Shutdown VRUN/SS = 400mV; IC is Shut Down 0.02 1 A RUN/SS Input Current - Active VRUN/SS = 5V; IC is Enabled 0.28 1 A PWM Threshold Measured at PWM Pin; Voltage at which Burst Mode Operation is Disabled (PWMing Enabled) 1 1.4 V PWM Input Current VPWM = 5V 1.25 2.5 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. 0.4 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. 3534fb For more information www.linear.com/LTC3534 3 LTC3534 Typical Performance Characteristics 4 Alkaline Cells to 5V Efficiency vs ILOAD USB to 5V Efficiency vs ILOAD 100 100 70 70 Burst 90 Mode OPERATION 80 EFFICIENCY (%) EFFICIENCY (%) Burst 90 Mode OPERATION 80 60 50 40 30 0.1 1 10 100 LOAD CURRENT (mA) 60 50 40 30 VIN = 3.6V VIN = 5V VIN = 6.4V 20 10 0.01 TA = 25C, unless otherwise noted. VIN = 4.35V VIN = 4.8V VIN = 5.25V 20 10 0.01 1000 0.1 1 10 100 LOAD CURRENT (mA) 3534 G01 3534 G02 Active Quiescent and Burst Mode SLEEP Currents vs VIN Current Limits vs VIN ACTIVE QUIESCENT CURRENT 415 28 26 405 Burst Mode SLEEP CURRENT 395 3.2 4.8 5.6 6.4 4 INPUT VOLTAGE (V) 7.2 24 8 22 VOUT = 5V 3.0 CURRENT LIMIT (A) VFB = 1.2V 385 2.4 3.3 30 Burst Mode SLEEP CURRENT (A) ACTIVE QUIESCENT CURRENT (A) 425 2.7 PEAK CURRENT LIMIT 2.4 2.1 LINEAR CURRENT LIMIT 1.8 1.5 2.4 3.2 4.8 5.6 6.4 4 INPUT VOLTAGE (V) 7.2 2.150 -25 0 50 25 TEMPERATURE (C) 75 100 3534 G05 50 VFB = 1.2V Burst Mode SLEEP CURRENT (A) ACTIVE QUIESCENT CURRENT (A) VIN START VOLTAGE (V) 450 2.175 2.125 -50 Burst Mode SLEEP Current vs Temperature Active Quiescent Current vs Temperature 2.200 430 410 390 370 -50 -25 8 3534 G04 3534 G03 Minimum Start-Up Voltage vs Temperature 1000 25 0 50 TEMPERATURE (C) 75 100 3534 G06 VFB = 1.2V 40 30 20 10 -50 -25 0 50 25 TEMPERATURE (C) 75 100 3534 G07 3534fb 4 For more information www.linear.com/LTC3534 LTC3534 Typical Performance Characteristics Converter Line Regulation vs Temperature Converter Load Regulation vs Temperature 5.01 5.000 4.995 4.990 4.985 3.6V 5.0V 6.4V 4.980 -25 25 0 50 TEMPERATURE (C) 75 100 VIN = 5V 1.000 4.99 300mA 4.98 500mA 4.97 0.998 4.95 -50 -25 25 0 50 TEMPERATURE (C) 75 100 3.0 50 2.8 PEAK CURRENT LIMIT CURRENT LIMIT (A) 2.5 2.3 2.0 LINEAR CURRENT LIMIT 975 1.8 1.5 -50 100 75 -25 25 0 50 TEMPERATURE (C) 3534 G11 OUTPUT CURRENT CAPABILITY (mA) PWM NO-LOAD INPUT CURRENT (mA) 10 6 3.2 4.8 5.6 6.4 4 INPUT VOLTAGE (V) 40 35 30 2.4 100 7.2 8 3534 G14 3.2 4.8 5.6 6.4 4 INPUT VOLTAGE (V) 8 PWM Maximum Output Current Capability vs VIN 1800 175 150 125 100 75 7.2 3534 G13 200 14 2 2.4 45 BURST Maximum Output Current Capability vs VIN VOUT = 5V 100 75 VOUT = 5V 3534 G12 PWM No-Load Input Current vs VIN (Switching) 18 75 OUTPUT CURRENT CAPABILITY (mA) 0 50 25 TEMPERATURE (C) 0 50 25 TEMPERATURE (C) BURST No-Load Input Current vs VIN (Switching) VIN = VOUT = 5V 1025 1000 -25 3534 G10 Current Limits vs Temperature 1050 -25 0.997 -50 3534 G09 Switching Frequency vs Temperature 950 -50 0.999 4.96 3534 G08 SWITCHING FREQUENCY (kHz) 25mA 5.00 BURST NO-LOAD INPUT CURRENT (A) 4.975 -50 Feedback Voltage vs Temperature 1.001 FB VOLTAGE (V) ILOAD = 100mA CONVERTER LOAD REGULATION (V) CONVERTER LINE REGULATION (V) 5.005 TA = 25C, unless otherwise noted. VOUT = 5V Burst Mode OPERATION 50 2.4 3.2 4.8 5.6 6.4 4 INPUT VOLTAGE (V) 7.2 8 3534 G15 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 3534 G16 3534fb For more information www.linear.com/LTC3534 5 LTC3534 Typical Performance Characteristics TA = 25C, unless otherwise noted. Load Transient Response in Fixed Frequency Mode, No-Load to 300mA VOUT Ripple at 300mA Load VOUT = 100mV/DIV VIN = 5V VIN = 3.6V VIN = 6.4V ILOAD = 100mA/DIV 3534 G17 1s/DIV VOUT = 5V, AC-COUPLED 20mV/DIV COUT = 22F ILOAD = 300mA 100s/DIV VIN = VOUT = 5V ILOAD = 0 TO 300mA COUT = 22F X5R CERAMIC 3534 G18 Transition from Burst Mode Operation to Fixed Frequency Mode Burst Mode Operation VOUT Ripple at 25mA Load VOUT = 50mV/DIV VOUT = 50mV/DIV INDUCTOR CURRENT = 200mA/DIV PWM = 2V/DIV 10s/DIV 3534 G19 100s/DIV VIN = VOUT = 5V COUT = 22F X5R CERAMIC 3534 G20 VIN = VOUT = 5V ILOAD = 25mA COUT = 22F X5R CERAMIC VOUT Start-Up VOUT = 2V/DIV RUN/SS = 1V/DIV (STARTS AT 1V) INDUCTOR CURRENT = 500mA/DIV PWM OPERATION MUST BE COMMANDED 500s/DIV 3534 G21 ILOAD = 100mA 3534fb 6 For more information www.linear.com/LTC3534 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. PWM mode operation must be commanded to properly enable the IC. 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. PWM must be driven HIGH during start-up. When VOUT is in regulation, the PWM pin may be driven LOW to command Burst Mode operation. Applying a voltage below 400mV enables Burst Mode operation, providing a significant efficiency improvement at light loads. 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. 3534fb For more information www.linear.com/LTC3534 7 LTC3534 Block Diagram L1 SW A CIN SW B PGND1 - PGND2 R2 VREF 1V - SUPPLY CURRENT LIMIT + PWM LOGIC AND OUTPUT PHASING UVLO - RZ VC CP2 CP1 14 + 2 SHUTDOWN AND SOFT-START ERROR AMP PWM COMPARATORS - - RSS CSS CZ1 15 THERMAL SHUTDOWN SHUTDOWN RUN/SS RFF AVERAGE CURRENT LIMIT + 2.2V R1 REVERSE CURRENT LIMIT FB + 2.6A 11 -500mA SW C + Gm = 1 100k VOUT 1.8V TO 7V COUT GATE DRIVERS AND ANTICROSS CONDUCTION VIN 1.8A VOUT SW D - 13 SW2 + 12 PVIN 6 ANTIRING - + + + + 5 SW1 + VIN 2.4V TO 7V 1MHz OSC Burst Mode OPERATION PWM 10 CONTROL SLEEP PGND1 GND EXPOSED PAD PGND2 4 3 17 7 3534 BD 3534fb 8 For more information www.linear.com/LTC3534 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. 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. LOW NOISE FIXED FREQUENCY OPERATION Reverse Current Limit Oscillator 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. 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 VOUT 12 11 PMOS A SW1 5 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 SW2 DMIN BOOST DMAX BUCK 6 NMOS B INTERNAL CONTROL VOLTAGE, VCI DUTY CYCLE 85% DMAX BOOST PMOS D L1 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. NMOS C 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) 0% 4 7 PGND1 PGND2 3534 F01 3534 F02 Figure 1. Simplified Diagram of Output Switches Figure 2. Switch Control vs Internal Control Voltage, VCI 3534fb For more information www.linear.com/LTC3534 9 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 offtime 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: 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) where f = operating frequency in Hz, typically 1MHz. 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. Hence, D4SW = 12.5% for the LTC3534. Burst Mode OPERATION DMAX_BUCK = (100 - D4SW)% where D4SW = duty cycle % of the four switch range. D4SW = (125ns * f) * 100% 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 = 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. VOUT V 1- (125ns * f ) 3534fb 10 For more information www.linear.com/LTC3534 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 125mA; Burst Mode operation - four switch region: VIN VOUT IOUT(MAX)BURST-BOOST 125 * VIN mA; VOUT 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: *ILOAD Efficiency 25A +ILOAD where h 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. Burst Mode Operation to Fixed Frequency Transient Response 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. The IC must be enabled (even with a soft-start) commanding PWM mode. Once the LTC3534 is in regulation, then Burst Mode operation can be commanded. In Burst Mode operation, the compensation network is not used and VC is disconnected from the error amplifier. VIN 13 ENABLE SIGNAL RSS VOUT RUN/SS + 2 ERROR AMP CSS - - VCI 1V R1 FB 15 VC + CHIP ENABLE 11 1V 14 CP1 R2 3534 F03 TO PWM COMPARATORS Figure 3. Soft-Start Circuitry 3534fb For more information www.linear.com/LTC3534 11 LTC3534 Applications Information COMPONENT SELECTION 2 RUN/SS FB 15 3 GND VC 14 4 PGND1 VIN 13 VIN 5 SW1 PVIN 12 6 SW2 VOUT 11 7 PGND2 PWM 10 VOUT PWM MULTIPLE VIAS 3534 F04 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 DIL = maximum allowable inductor ripple current, A 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: VIN(MIN) = minimum input voltage, V LBOOST > LBUCK > ( VIN(MIN) * VOUT - VIN(MIN) ( f * IL * VOUT VOUT * VIN(MAX) - VOUT f * IL * VIN(MAX) )H )H where f = switching frequency in Hz, typically 1MHz. 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. Table 1. Inductor Vendor Information SUPPLIER PHONE FAX OR E-MAIL WEBSITE Coilcraft (847) 639-6400 (847) 639-1469 www.coilcraft.com FDK (408) 432-8331 america@fdk.com www.fdk.com Murata (814) 237-1431 (800) 831-9172 (814) 238-0490 www.murata.com Sumida USA: (847) 956-0702 www.sumida.com USA: (847) 956-0666 Japan: 81(3) 3607-5111 Japan: 81(3) 3607-5144 TDK (847) 803-6100 (847) 803-6296 www.component.tdk.com TOKO (847) 297-0070 (847) 699-7864 www.tokoam.com 3534fb 12 For more information www.linear.com/LTC3534 LTC3534 Applications Information Output Capacitor Selection Input 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: 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. VP-P Boost = VP-P Buck = ( IOUT * VOUT - VIN(MIN) COUT * VOUT * f 1 8 *L *COUT * f * 2 )V ( VIN(MAX) - VOUT ) * VOUT V VIN(MAX) 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 FAX WEBSITE AVX (803) 448-9411 (803) 448-1943 www.avxcorp.com Sanyo (619) 661-6322 (619) 661-1055 www.sanyovideo.com Taiyo Yuden (408) 573-4150 (408) 573-4159 www.t-yuden.com TDK (847) 803-6100 (847) 803-6296 www.component.tdk.com 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 = 1 Hz (in buck mode) 2 * * L1*COUT fFILTER _ POLE = VIN Hz (in boost mode) 2 * VOUT * * L1*COUT where L1 is in Henries and COUT is in Farads. The output filter zero is given by: 3534fb For more information www.linear.com/LTC3534 13 LTC3534 Applications Information fFILTER _ ZERO = 1 2 * *RESR *COUT 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: fRHPZ = fPOLE1 1 2 * * 5x103 *R1*CP1 Hz (which is extremely close to DC) VIN 2 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 = 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: f ZERO1 = 1 Hz 2 * *R Z *CP1 f ZERO2 = 1 Hz 2 * *R1*CZ1 fPOLE2 = 1 Hz 2 * *R Z *CP2 where resistance is in Ohms and capacitance is in Farads. 1 Hz 2 * *R1*CP1 Most applications demand an improved transient response VOUT VOUT + ERROR AMP - 11 1V + ERROR AMP - R1 FB VC 14 CP1 CP1 RZ R2 CP2 3534 F06 3534 F05 Figure 5. Error Amplifier with Type I Compensation R1 15 14 R2 CZ1 FB VC 15 11 1V Figure 6. Error Amplifier with Type III Compensation 3534fb 14 For more information www.linear.com/LTC3534 LTC3534 Typical Applications 4 Alkaline/NiMH to 5V at 500mA L1 5H VIN 3.6V TO 6.4V 4 ALKALINE/ NiMH CELLS + CIN RSS 200k 10F SW1 SW2 PVIN VIN VOUT RFF 10k CZ1 33pF LTC3534 RUN/SS CSS 0.056F *BURST PWM PWM FB VOUT 5V 500mA COUT 22F R1 649k CP1 330pF RZ 15k VC CP2 10pF R2 162k PGND1 GND PGND2 L1: COILCRAFT MSS7341 3534 TA02a *PWM MUST BE DRIVEN HIGH DURING START-UP. WHEN VOUT IS IN REGULATION, THE PWM PIN MAY BE DRIVEN LOW TO COMMAND BURST MODE OPERATION. 4 Alkaline/NiMH Cells to 5V Efficiency vs ILOAD 100 EFFICIENCY (%) Burst 90 Mode OPERATION 80 70 60 50 40 30 VIN = 3.6V VIN = 5V VIN = 6.4V 20 10 0.01 0.1 1 10 100 LOAD CURRENT (mA) 1000 3534 TA02b 3534fb For more information www.linear.com/LTC3534 15 LTC3534 Typical Applications USB to 5V at 500mA L1 5H USB to 5V Efficiency vs ILOAD 100 RSS CIN 200k 10F SW2 PVIN VIN VOUT LTC3534 FB RUN/SS CSS 0.056F *BURST PWM VC PWM RFF 10k CZ1 33pF Burst 90 Mode OPERATION 80 VOUT 5V 500mA** COUT 22F EFFICIENCY (%) USB 4.35V TO 5.25V SW1 R1 649k CP1 330pF RZ 15k 70 60 50 40 30 CP2 10pF VIN = 4.35V VIN = 4.8V VIN = 5.25V 20 10 0.01 R2 162k PGND1 GND PGND2 L1: COILCRAFT MSS7341 0.1 1 10 100 LOAD CURRENT (mA) 1000 3534 TA03b 3534 TA03a *PWM MUST BE DRIVEN HIGH DURING START-UP. WHEN VOUT IS IN REGULATION, THE PWM PIN MAY BE DRIVEN LOW TO COMMAND BURST MODE OPERATION. **NOTE: OUTPUT CURRENT CAN BE LESS THAN 500mA IF USB INPUT CURRENT LIMIT REACHED. Li-Ion to 3.3V at 400mA L1 3.3H Li-Ion to 3.3V Efficiency vs ILOAD 100 1 Li-Ion CELL + RSS 200k CSS 0.056F *BURST PWM CIN 10F SW2 PVIN VIN VOUT LTC3534 RUN/SS PWM FB VC COUT 22F RFF 10k R1 374k CZ1 66pF CP1 470pF RZ 15k 70 60 50 40 30 CP2 10pF VIN = 2.7V VIN = 3.6V VIN = 4.2V 20 R2 162k PGND1 GND PGND2 L1: TDK RLF7030 Burst 90 Mode OPERATION 80 VOUT 3.3V 400mA EFFICIENCY (%) VIN 2.7V TO 4.2V SW1 3534 TA04a 10 0.01 0.1 1 10 100 LOAD CURRENT (mA) 1000 3534 TA04b *PWM MUST BE DRIVEN HIGH DURING START-UP. WHEN VOUT IS IN REGULATION, THE PWM PIN MAY BE DRIVEN LOW TO COMMAND BURST MODE OPERATION. 3534fb 16 For more information www.linear.com/LTC3534 LTC3534 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. DHC Package 16-Lead Plastic DFN (5mm x 3mm) (Reference LTC DWG # 05-08-1706 Rev O) 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) 9 R = 0.115 TYP 0.40 0.10 16 1.65 0.10 (2 SIDES) PIN 1 TOP MARK (SEE NOTE 6) PIN 1 NOTCH 0.200 REF 0.75 0.05 0.00 - 0.05 8 1 0.25 0.05 0.50 BSC (DHC16) DFN 1103 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 3534fb For more information www.linear.com/LTC3534 17 LTC3534 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. GN Package 16-Lead Plastic SSOP (Narrow .150 Inch) (Reference LTC DWG # 05-08-1641 Rev B) .189 - .196* (4.801 - 4.978) .045 .005 16 15 14 13 12 11 10 9 .254 MIN .009 (0.229) REF .150 - .165 .229 - .244 (5.817 - 6.198) .0165 .0015 .150 - .157** (3.810 - 3.988) .0250 BSC RECOMMENDED SOLDER PAD LAYOUT 1 .015 .004 x 45 (0.38 0.10) .007 - .0098 (0.178 - 0.249) .0532 - .0688 (1.35 - 1.75) 2 3 4 5 6 7 8 .004 - .0098 (0.102 - 0.249) 0 - 8 TYP .016 - .050 (0.406 - 1.270) .008 - .012 (0.203 - 0.305) TYP NOTE: 1. CONTROLLING DIMENSION: INCHES INCHES 2. DIMENSIONS ARE IN (MILLIMETERS) .0250 (0.635) BSC GN16 REV B 0212 3. DRAWING NOT TO SCALE 4. PIN 1 CAN BE BEVEL EDGE OR A DIMPLE *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 3534fb 18 For more information www.linear.com/LTC3534 LTC3534 Revision History (Revision history begins at Rev B) REV DATE DESCRIPTION B 02/14 Updated BURST Maximum Output Current Capability vs VIN curve. PAGE NUMBER 5 Added note to VOUT Start-Up scope photo. 6 Modified RUN/SS and PWM pin descriptions. 7 Modified Burst Mode current equations and Soft-Start section. 11 Added start-up conditions to Typical Applications figures. 15, 16 3534fb 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. For more information www.linear.com/LTC3534 19 LTC3534 Related Parts PART NUMBER DESCRIPTION COMMENTS LTC3125 1.2A (ISW), 1.5MHz, Synchronous Step-Up DC/DC Converter with Programmable Input Current 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 LTC3421 3A (ISW), 3MHz, Synchronous Step-Up DC/DC Converter with Output Disconnect 96% Efficiency, VIN: 0.5V to 4.5V, VOUT(MAX) = 5.25V, IQ = 12A, ISD <1A, QFN24 Package LTC3422 1.5A (ISW), 3MHz, Synchronous Step-Up DC/DC Converter with Output Disconnect 96% Efficiency, VIN: 0.5V to 4.5V, VOUT(MAX) = 5.25V, IQ = 25A, ISD <1A, DFN10 Package LTC3425 5A (ISW), 8MHz (Low Ripple), 4-Phase Synchronous Step-Up DC/DC Converter with Output Disconnect 95% Efficiency, VIN: 0.5V to 4.5V, VOUT(MAX) = 5.25V, IQ = 12A, ISD <1A, QFN32 Package LTC3429 600mA (ISW), 500KHz, Synchronous Step-Up DC/DC Converter with Output Disconnect and Soft-Start 96% Efficiency, VIN: 0.5V to 4.4V, VOUT(MAX) = 5V, IQ = 20A, ISD <1A, ThinSOT-23 Package LTC3440 600mA (IOUT), 2MHz, Synchronous Buck-Boost DC/DC Converter 96% Efficiency, VIN: 2.5V to 5.5V, VOUT(MAX) = 5.5V, IQ = 25A, ISD <1A, MSOP and DFN Packages LTC3441/LTC3443 1.2A (IOUT), 1MHz/600kHz, Synchronous Buck-Boost DC/DC Converter 95%/96% Efficiency, VIN: 2.4V to 5.5V, VOUT(MAX) = 5.25V, IQ = 35A/28A, ISD <1A, MSOP Packages LTC3442 1.2A (IOUT), 2MHz, Synchronous Buck-Boost DC/DC Converter 95% Efficiency, VIN: 2.4V to 5.5V, VOUT(MAX) = 5.25V, IQ = 25A, ISD <1A, DFN Package LTC3444 400mA (IOUT), 1.5MHz, Synchronous Buck-Boost DC/DC Converter with wide VOUT Range 93% Efficiency, VIN: 2.7V to 5.5V, VOUT: 0.5V to 5V, ISD <1A, DFN Package, Ideal for WCDMA PA Bias LTC3520 1A (IOUT), 2MHz Synchronous Buck-Boost, 600mA Buck DC/DC Converter 95% Efficiency, VIN: 2.2V to 5.5V, VOUT(MAX) = 5.25V, VOUT(MIN) = 0.8V; IQ = 55A, ISD < 1A, QFN Package LTC3522 Synchronous 400mA (IOUT) Buck-Boost and 200mA (IOUT) Buck, 1MHz, DC/DC Converters 95% Efficiency, VIN: 2.4V to 5.5V, VOUT(MAX) = 5.25V, VOUT(MIN) = 0.6V; IQ = 25A, ISD <1A, QFN Package LTC3526L 500mA (IOUT), 1MHz Synchronous Step-Up DC/DC Converter with Output Disconnect 94% Efficiency, VIN: 0.8V to 5V, VOUT(MAX) = 5.25V, IQ = 9A, ISD <1A, 2mm x 2mm DFN-6 Package LTC3530 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 LTC3531 200mA (IOUT), Burst Mode Operation, Synchronous Buck-Boost DC/DC Converter with Adjustable and Fixed VOUT Versions 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 LTC3532 500mA (IOUT), 2MHz, Synchronous Buck-Boost DC/DC Converter 95% Efficiency, VIN: 2.4V to 5.5V, VOUT(MAX) = 5.25V, IQ = 35A, ISD <1A, MSOP and DFN Packages LTC3533 2A (IOUT), 2MHz, Synchronous Buck-Boost DC/DC Converter with Wide Input Voltage Range 96% Efficiency, VIN: 1.8V to 5.5V, VOUT(MAX) = 5.25V, IQ = 40A, ISD <1A, MSOP and DFN Packages LTC3538 800mA (IOUT), 1MHz, Synchronous Buck-Boost DC/DC Converter 95% Efficiency, VIN: 2.4V to 5.5V, VOUT(MAX) = 5.25V, IQ = 35A, ISD = 1.5A, DFN Package 3534fb 20 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 For more information www.linear.com/LTC3534 (408) 432-1900 FAX: (408) 434-0507 www.linear.com/LTC3534 LT 0214 REV B * PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 2009