LTC3533 2A Wide Input Voltage Synchronous Buck-Boost DC/DC Converter DESCRIPTION FEATURES Regulated Output with Input Voltages Above, Below or Equal to the Output n 1.8V to 5.5V (Input) and 5.25V (Output) Voltage Range n 0.8A Continuous Output Current: V > 1.8V IN n 2A Continuous Output Current: V > 3V IN n Single Inductor n Synchronous Rectification: Up to 96% Efficiency n Programmable Burst Mode® Operation: I = 40µA Q n Output Disconnect in Shutdown n Programmable Frequency from 300kHz to 2MHz n <1µA Shutdown Current n Small Thermally Enhanced 14-Lead (3mm × 4mm × 0.75mm) DFN package The LTC®3533 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 single cell lithium-ion/polymer or multi-cell alkaline/NiMH applications where the output voltage is within the input voltage range. APPLICATIONS Other features include 1µA shutdown current, short circuit protection, programmable soft-start, current limit and thermal shutdown. The LTC3533 is housed in the thermally enhanced 14-lead (3mm × 4mm × 0.75mm) DFN package. n n n n n n n GSM Modems Handheld Instruments Digital Cameras Smart Phones Media Players Miniature Hard Disk Drive Power The LTC3533 features programmable Burst Mode operation, extended VIN and VOUT ranges down to 1.8V, and increased output current. Switching frequencies up to 2MHz are programmed with an external resistor. The Burst Mode threshold is programmed with a single resistor from the BURST pin to GND. L, LT, LTC, LTM and BurstMode are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. TYPICAL APPLICATION 2.2μH SW1 SW2 PVIN PVOUT VIN VOUT 100 340k 47pF LTC3533 OFF ON RUN/SS RT 10μF 6.49k FB VC 107k 330pF 100μF 4.7pF 33.2k PGND 90 80 70 60 50 Burst Mode OPERATION VIN = 2.9V VIN = 2.2V 40 VIN = 3.9V 30 20 BURST SGND VOUT 3.3V 1.5A EFFICIENCY (%) VIN 2.4V TO 4.2V Efficiency 10 0.1μF 200k 200k 0 0.1 3533 TA01 1 10 100 1000 OUTPUT CURRENT (mA) 10000 3533 TA01b 3533fb 1 LTC3533 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) TOP VIEW VIN, PVIN Voltages............................................–0.3 to 6V VOUT, PVOUT Voltages......................................–0.3 to 6V SW1, SW2 Voltages DC................................................................–0.3 to 6V Pulsed < 100ns............................................–0.3 to 7V VC, FB, RUN/SS, BURST Voltages...................–0.3 to 6 V Operating Temperature Range (Note 2).... –40°C to 85°C Maximum Junction Temperature (Note 3)............. 125°C Storage Temperature Range.................... –65°C to 125°C RT 1 14 VC BURST 2 13 FB SGND 3 SW1 4 PGND 5 10 VIN PGND 6 9 PVOUT SW2 7 8 VOUT 12 RUN/SS 15 11 PVIN DE PACKAGE 14-LEAD (4mm × 3mm) PLASTIC DFN TJMAX = 125°C, θJA = 43°C/W, θJC = 4.3°C/W EXPOSED PAD (PIN 15) IS GND, MUST BE SOLDERED TO PCB ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LTC3533EDHC#PBF LTC3533EDHC#TRPBF 3533 14-Lead (4mm × 3mm) Plastic DFN –40°C to 85°C LEAD BASED FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LTC3533EDHC LTC3533EDHC#TR 3533 14-Lead (4mm × 3mm) Plastic DFN –40°C to 85°C 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/. Some packages are available in 500 unit reels through designated sales channels with #TRMPBF suffix. The ELECTRICAL CHARACTERISTICS l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 3.6V, VOUT = 3.3V, unless otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS Input Operating Range l 1.8 5.5 V Output Voltage Adjust Range l 1.8 5.25 V Feedback Voltage l 1.196 1.22 1.244 V Feedback Input Current VFB = 1.22V 1 50 nA Quiescent Current – Burst Mode Operation VC = 0V, VBURST = 0V (Note 4) 40 50 µA Quiescent Current – Shutdown VRUN = 0V, Not Including Switch Leakage 0.1 1 µA Quiescent Current – Active VC = 0V, BURST = 3.6V (Note 4) 700 1100 µA Input Current Limit l Peak Current Limit Reverse Current Limit 3.5 4.5 A 7 A 0.5 A NMOS Switch Leakage Switches B and C 0.1 5 µA PMOS Switch Leakage Switches A and D 0.1 10 µA NMOS Switch On Resistance Switches B and C 60 mW PMOS Switch On Resistance Switches A and D 80 mW 2 3533fb LTC3533 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 3.6V, VOUT = 3.3V, unless otherwise noted. PARAMETER CONDITIONS Maximum Duty Cycle Boost (% Switch C On) Buck (% Switch A On) l l Minimum Duty Cycle Frequency Accuracy MIN TYP 80 100 90 l 0.7 1 UNITS % % 0 l RT = 33.2k MAX 1.3 % MHz Error Amp AVOL 80 dB Error Amp Source Current –20 µA Error Amp Sink Current 250 µA 1 V Burst Threshold Burst Input Current VBURST = 5.5V, VIN = 5.5V RUN/SS Threshold When IC is Enabled When EA is at Maximum Boost Duty Cycle RUN/SS Input Current VRUN = 5.5V 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. Note2: The LTC3533EDE is guaranteed to meet performance specifications from 0ºC to 85ºC. Specifications over the –40ºC to 85ºC operating temperature range are assured by design, characterization and correlation with statistical process controls. l 0.4 8 µA 0.7 1.3 1.4 V V 0.01 1 µA Note 3: This IC includes over-temperature protection that is intended to protect the device during momentary overload conditions. Junction temperature will exceed 125°C when over-temperature protection is active. Continuous operation above the specified maximum operating junction temperature may result in device degradation or failure. Note 4: Current Measurements are performed when the outputs are not switching. 3533fb 3 LTC3533 TYPICAL PERFORMANCE CHARACTERISTICS Quiescent Current vs VIN (Fixed Frequency Mode) 3.0 1.5 MHz 1.0 MHz 2.0 1.5 0.5 MHz 1.0 NO SWITCHING 50 5 45 4 40 3 CURRENT LIMIT CHANGE (%) VIN QUIESCENT CURRENT (μA) VIN QUIESCENT CURRENT (mA) 2.0 MHz 2.5 35 30 25 20 15 10 2 1 0 –1 –2 –3 0.5 5 –4 0.0 2.5 0 –5 –55 –35 –15 3.0 3.5 4.0 VIN (V) 4.5 5.0 5.5 2.5 3.0 3.5 4.0 VIN (V) 4.5 5.0 5.5 3533 G03 Minimum Start Voltage vs Temperature Automatic Burst Mode Threshold vs RBURST Average Input Current Limit vs Temperature 1.84 200 100 ENTER Burst Mode OPERATION 50 0 100 125 150 175 200 RBURST (kΩ) 225 4 3 CHANGE FROM 25°C (%) LEAVE Burst Mode OPERATION 5 1.82 MINIMUM START VOLTAGE (V) 150 5 25 45 65 85 105 125 TEMPERATURE (°C) 3530 G02 3533 G01 LOAD CURRENT (mA) Peak Current Limit vs Temperature Burst Mode Quiescent Current 4.0 3.5 TA = 25°C, unless otherwise specified. 1.80 1.78 1.76 1.74 1.72 1 0 –1 –2 –3 –4 1.70 –45 –25 –5 250 2 15 35 55 75 TEMPERATURE (°C) 95 115 –5 –55 –35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) 3533 G05 3533 G04 Frequency Change vs Temperature 3533 G06 Switch Pins Before Entering Boost Mode Feedback Voltage vs Temperature 1.076 1.2250 1.074 FEEDBACK VOLTAGE (V) FREQUENCY (MHz) 1.072 1.070 1.068 1.066 1.064 1.062 1.2200 SW1 2V/DIV 1.2150 SW2 2V/DIV 1.060 1.058 1.056 –55 –35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) 3533 G07 4 1.2100 –55 –35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) 3533 G08 50ns/DIV 3533 G09 VIN = 2.9V VOUT = 3.3V AT 500mA 3533fb LTC3533 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise specified. Switch Pins Entering Buck-Boost Mode Switch Pins in Buck-Boost Mode SW1 2V/DIV SW1 2V/DIV Output Ripple at 1A Load VIN = 2.7V VIN = 3.3V SW2 2V/DIV SW2 2V/DIV 50ns/DIV VIN = 3.3V VOUT = 3.3V AT 500mA VIN = 4.2V 3533 G10 50ns/DIV 3533 G11 VIN = 4.2V VOUT = 3.3V AT 500mA Load Transient Response in Fixed Frequency Mode, No Load to 1.5A 1μs/DIV VOUT = 3.3V, 20mV/DIV COUT = 100μF CERAMIC 3533 G12 Load Transient Response in Auto Burst Mode, No Load to 600mA VOUT 100mV/DIV VOUT 100mV/DIV IL 0.5A/DIV LOAD 0.5A/DIV 100μs/DIV VIN = 3.6V VOUT = 3.3V COUT = 100μF X5R CERAMIC 100μs/DIV VIN = 3.6V VOUT = 3.3V COUT = 100μF X5R CERAMIC + 100μF LOW ESR TANTALUM 3533 G13 Transition from Burst Mode Operation to Fixed Frequency Mode Burst Mode Operation VOUT 50mV/DIV VOUT 50mV/DIV INDUCTOR CURRENT 0.5A/DIV INDUCTOR CURRENT 0.5A/DIV 20μs/DIV COUT = 100μF CERAMIC 3533 G14 3533 G15 200μs/DIV COUT = 100μF CERAMIC 3533 G16 3533fb 5 LTC3533 PIN FUNCTIONS RT (Pin 1): Programs the Frequency of the Internal Oscillator. Connect a resistor from RT to ground. f(kHz) = 33,170/RT (kΩ) BURST (Pin 2): Used to set the Automatic Burst Mode Threshold. Connect a resistor and capacitor in parallel from this pin to ground. See the Applications Information section for component value selection. For manual control, ground the pin to force Burst Mode operation, connect to VIN to force fixed frequency PWM mode. SGND (Pin 3): Signal ground for the IC. SW1 (Pin 4): Switch Pin where Internal Switches A and B are Connected. Connect inductor from SW1 to SW2. An optional Schottky diode can be connected from SW1 to ground for a moderate efficiency improvement. Minimize trace length to reduce EMI. PGND1, PGND2 (Pins 5, 6): Power Ground for the Internal NMOS Power Switches. SW2 (Pin 7): Switch Pin where Internal Switches C and D are Connected. An optional Schottky diode can be connected from SW2 to VOUT for a moderate efficiency improvement. For applications with output voltages over 4.3V, this Schottky diode is required to ensure the SW2 pin does not exhibit excess voltage. Minimize trace length to reduce EMI. VOUT (Pin 8): Voltage Sensing Pin for PVOUT and Input Supply Pin for Internal Circuitry Powered by PVOUT. 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. 6 PVOUT (Pin 9): Output of the Synchronous Rectifier. A filter capacitor is placed from PVOUT to PGND. A ceramic bypass capacitor is recommended as close to the PVOUT and PGND pins as possible. VIN (Pin 10): Input Supply Pin. Internal VCC for the IC. PVIN (Pin 11): Power VIN Supply Pin. A 10µF ceramic capacitor is recommended as close to the PVIN and PGND pins as possible. RUN/SS (Pin 12): Combined Enable and Soft-Start. Applied voltage <0.4V shuts down the IC. Tie to >1.4V to enable the IC and >1.6V 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 VC FB (Pin 13): Feedback Pin. Connect resistor divider tap here. The output voltage can be adjusted from 1.8V to 5.25V. The feedback reference voltage is typically 1.22V. VOUT = 1.22 • R1+ R2 R2 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. During Burst Mode operation, VC is internally connected to a hold circuit. Exposed Pad (Pin 15): IC Substrate Ground. This pin must be soldered to the PCB ground to provide both electrical contact and a good thermal contact to the PCB. 3533fb LTC3533 BLOCK DIAGRAM SW2 SW1 VOUT SW D SW B GATE DRIVERS AND ANTI-CROSS CONDUCTION –0.5A SW C – SW A ISENSE AMP + VIN 1.8V TO 5.5V REVERSE CURRENT LIMIT R1 + + SUPPLY CURRENT LIMIT + + ERROR AMP – – – 4.5A UVLO + RT VC + R2 OSC SLEEP BURST MODE OPERATION CONTROL BURST 0 = BURST MODE 1 = FIXED FREQUENCY CLAMP FB – – 1.6V RT PWM LOGIC AND OUTPUT PHASING PWM COMPARATORS 1.22V RUN GND RUN/SS RSS VIN CSS 3533 BD 3533fb 7 LTC3533 OPERATION The LTC3533 provides high efficiency, low noise power for a wide variety of handheld electronic devices. The LTC 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 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 entered and the LTC3533’s quiescent current drops to a low 40µA. LOW NOISE FIXED FREQUENCY OPERATION Oscillator The first circuit is a current limit amplifier, sourcing current into FB to drop the output voltage, should the peak input current exceed 4.5A 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 startup, this threshold is cut to 750mA, providing a fold-back 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 7A 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 f(kHz) = 33,170/RT(k) During fixed frequency operation, the LTC3533 operates in forced continuous conduction mode. The reverse current limit comparator monitors the inductor current from the output through switch D. Should this negative inductor current exceed 500mA typical, the LTC3533 shuts off switch D. Error Amplifier Four-Switch Control 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 RC feed-forward network can be placed across the upper feedback divider resistor. The voltage on the RUN/SS pin clamps the error amplifier output, VC, to provide a soft-start function. 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 LTC3533 as a function of the control voltage, VC. The frequency of operation is programmed by an external resistor from RT to ground, according to the following equation: Supply Current Limits There are two different supply current limit circuits in the LTC3533, working consecutively, each having internally fixed thresholds which vary inversely with VIN. 8 Dependent on VC’s magnitude, the LTC3533 will operate in either buck, buck/boost or boost mode. 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 150ns. Referring to Figures 1 and 2, the various regions of operation will now be described. 3533fb LTC3533 OPERATION PVIN PVOUT 11 9 PMOS A SW1 where D4SW = duty cycle % of the four switch range. D4SW = (150ns • f) • 100 % PMOS D L1 SW2 3 7 NMOS B NMOS C Figure 1. Simplified Diagram of Output Switches V4 (≈1.5V) A ON, B OFF BOOST REGION PWM CD SWITCHES DMIN BOOST DMAX BUCK V3 (≈1.15V) FOUR SWITCH PWM Beyond this point the “four switch,” or buck/boost region is reached. Buck/Boost or Four Switch (VIN ~ VOUT) 3533 F01 85% DMAX BOOST where f = operating frequency, Hz. BUCK/BOOST REGION V2 (≈1V) D ON, C OFF PWM AB SWITCHES BUCK REGION When the control voltage, VC, is above voltage V2, switch pair AD remain on for duty cycle DMAX_BUCK, and switch pair AC begins to phase in. As switch pair AC phases in, switch pair BD phases out accordingly. When VC 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(1 – D) = VOUT(1 – 150ns • f) V The point at which the four switch region ends is given by: V1 (≈0.7V) 0% DUTY CYCLE 3533 F02 CONTROL VOLTAGE, VC Figure 2. Switch Control vs Control Voltage, VC Buck Region (VIN > VOUT) Switch D is always on and switch C is always off during this mode. When the control voltage, VC, is above voltage V1, switch 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: VIN = VOUT V 1− (150ns • f) where f = operating frequency, Hz. Boost Region (VIN < VOUT) Switch A is always on and switch B is always off during this mode. When the control voltage, VC, 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 90% typical and is reached when VC is above V4. DMAX_BUCK = 100 – D4SW % 3533fb 9 LTC3533 OPERATION BURST MODE OPERATION Programmable Automatic Burst Mode Operation Burst Mode operation reduces the LTC3533’s quiescent current consumption at light loads and improves overall conversion efficiency, increasing battery life. During Burst Mode operation the LTC3533 delivers energy to the output until it is regulated and then goes into a sleep mode where the outputs are off and the quiescent current drops to 40µA. 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. Another method of reducing Burst Mode operation ripple is to place a small feed-forward capacitor across the upper resistor in the VOUT feedback divider network (as in Type III compensation). Burst Mode operation can be automatic or digitally controlled with a single pin. In automatic mode, the LTC3533 enters Burst Mode operation at the programmed threshold and returns to fixed frequency operation when the load demand increases. The load current at which the mode transition occurs is programmed using a single external resistor from BURST to ground, according to the following equations: During the period where the device is delivering energy to the output, the peak switch current will rise to 900mA typical and the inductor current will terminate at zero current for each cycle. In this mode, the typical maximum average output currents are given by: Where RBURST is in kΩ and IBURST is the load transition current in Amps. Do not use values of RBURST greater than 250kΩ. IMAX(BURST)BUCK ≈ 450mA; VOUT < VIN Enter Burst Mode Operation: I BURST = The efficiency below 1mA becomes dominated primarily by the quiescent current. The Burst Mode operation efficiency is given by: Efficiency ≅ η •ILOAD 40µA +ILOAD where h is typically 90% during Burst Mode operation 10 RBURST 19 RBURST For automatic operation a filter capacitor must also be connected from BURST to ground. The equation for the minimum capacitor value is: IMAX(BURST)BOOST ≈ 450mA • (VIN/VOUT); VOUT > VIN IMAX(BURST)BUCK-BOOST ≈ 700mA; VOUT ≈ VIN, since the input and output are connected together for most of the cycle. Exit Burst Mode Operation: I BURST = 17 CBURST(MIN) ≥ COUT • VOUT 60,000 where CBURST(MIN) and COUT are in µF. In the event that a load transient causes FB to drop by more than 4% from the regulation value while in Burst Mode operation, the LTC3533 will immediately switch to fixed frequency mode and an internal pull-up will be momentarily applied to BURST, rapidly charging CBURST. This prevents the IC from immediately re-entering Burst mode operation once the output achieves regulation. 3533fb LTC3533 OPERATION Manual Burst Mode Operation For manual control of Burst Mode operation, the RC network connected to BURST can be eliminated. To force fixed frequency mode, BURST should be connected to VIN. To force Burst Mode operation, BURST should be grounded. When commanding Burst Mode operation manually, the circuit connected to BURST should be able to sink up to 2mA. For optimum transient response with large dynamic loads, the operating mode should be controlled digitally by the host. By commanding fixed frequency operation prior to a sudden increase in load, output voltage droop can be minimized. Note that if the load current applied during forced Burst Mode operation (BURST pin is grounded) exceeds the current that can be supplied, the output voltage will start to droop and the LTC3533 will automatically come out of Burst Mode operation and enter fixed frequency mode, raising VOUT. Once regulation is achieved, the LTC3533 will then enter Burst Mode operation once again (since the user is still commanding this by grounding BURST), and the cycle will repeat, resulting in about 4% output ripple. 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 3 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 LTC3533 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 above 1.6V. VIN RUN/SS VC 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 of operation, even at the same load current. To prevent this, the LTC3533 3533 F03 Figure 3. 3533fb 11 LTC3533 APPLICATIONS INFORMATION COMPONENT SELECTION where f = switching frequency, Hz ∆IL = maximum allowable inductor ripple current 1 RT VC 14 VIN(MIN) = minimum input voltage 2 BURST FB 13 VIN(MAX) = maximum input voltage 3 SGND RUN/SS 12 4 SW1 PVIN 11 5 PGND VIN 10 6 PGND PVOUT 9 7 SW2 VOUT 8 GND VOUT = output voltage VIN VOUT MULTIPLE VIAS 3533 F04 Figure 4. Recommended Component Placement. Traces Carrying High Current Should be Short and Wide. Trace Area at FB and VC Pins are Kept Low. Lead Length to Battery Should be Kept Short. PVOUT and PVIN Ceramic Capacitors Close to the IC Pins. Inductor Selection The high frequency operation of the LTC3533 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 • ΔIL • VOUT VOUT • (VIN(MAX) − VOUT ) f • ΔIL • VIN(MAX) H For high efficiency, choose a ferrite inductor with a high frequency core material to reduce core losses. 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 4A to 6A region. To minimize radiated noise, use a shielded inductor. See Table 1 for a suggested list of inductor suppliers. 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: %Ripple _Boost = %Ripple _Buck = IOUT(MAX) • (VOUT − VIN(MIN) ) • 100 COUT • VOUT 2 • f (VIN(MAX) − VOUT ) • 100 8L COUT • VIN(MAX) • f 2 % % where COUT = output filter capacitor IOUT(MAX) = maximum output load current H The output capacitance is usually many times larger than the minimum value in order to handle the transient response Table 1. Inductor Vendor Information SUPPLIER PHONE FAX WEB SITE Coilcraft (847) 639-6400 (847) 639-1469 www.coilcraft.com CoEv Magnetics (800) 227-7040 (650) 361-2508 www.circuitprotection.com/magnetics.asp Murata (814) 237-1431 (800) 831-9172 (814) 238-0409 www.murata.com Sumida USA: (847) 956-0666 Japan: 81(3) 3607-5111 USA: (847) 956-0702 Japan: 81(3) 3607-5144 www.sumida.com TDK (847) 803-6100 (847) 803-6296 www.component.tdk.com TOKO (847) 297-0070 (847) 699-7864 www.tokoam.com 12 3533fb LTC3533 APPLICATIONS INFORMATION 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. to provide the conduction path to the output. Note that Burst Mode operation is inhibited at output voltages below 1V typical. 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. A Schottky diode from SW2 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 parasitic lead and trace inductances. Output Voltage > 4.3V Input Voltage > 4.5V Since PVIN is the supply voltage for the IC it is recommended to place at least a 4.7µF, low ESR ceramic bypass capacitor close to PVIN and GND. It is also important to minimize any stray resistance from the converter to the battery or other power source. For applications with input voltages above 4.5V which could exhibit an overload or short-circuit condition, a 2W/1nF series snubber is required between SW1 and GND. A Schottky diode from SW1 to PVIN 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 PVIN and GND pins as possible is also required. Optional Schottky Diodes Operating Frequency Selection 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. Higher operating frequencies allow the use of a smaller inductor and smaller input and output filter capacitors, thus reducing board area and component height. However, higher operating frequencies also increase the IC’s total quiescent current due to the gate charge of the four switches, as given by: Output Voltage < 1.8V Boost:IQ = [800e – 12 • (VIN + VOUT) • f ] mA The LTC3533 can operate as a buck converter with output voltages as low as 400mV. The part is specified at 1.8V minimum to allow operation without the requirement of a Schottky diode; Since synchronous switch D is powered from PVOUT, and the RDS(ON) will increase at low output voltages, a Schottky diode is required from SW2 to VOUT Buck/Boost:IQ = [(1400e – 12 • VIN + 400e – 12 • VOUT) • f ] mA Input Capacitor Selection Buck:IQ = (600e – 12 • VIN • f ) mA where f = switching frequency in Hz. Therefore frequency selection is a compromise between the optimal efficiency and the smallest solution size. Table 2. Capacitor Vendor Information SUPPLIER PHONE FAX WEB SITE 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 3533fb 13 LTC3533 APPLICATIONS INFORMATION Closing the Feedback Loop The LTC3533 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: f FILTER _POLE = 1 Hz 2 • π • L • COUT (in buckm ode) f FILTER _POLE = VIN Hz 2 • VOUT • π • L • COUT (in boostm ode) where L is in Henries and COUT is in Farads. The output filter zero is given by: f FILTER _ ZERO = 1 2 • π • RESR • COUT Hz A troublesome feature in boost mode is the right-half plane zero (RHP), given by: f UG = 1 Hz 2 • π • 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, 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: 1 f POLE1 = where RESR is the equivalent series resistance of the output capacitor. f RHPZ = 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 with the Type I compensation is given by: VIN2 Hz 2 • π •IOUT • L • VOUT The loop gain is typically rolled off before the RHP zero frequency. Hz 2 • π • 10e3 • R1• CP1 (which is a very low frequency) 1 Hz f ZERO1 = 2 • π • R Z • CP1 1 Hz f ZERO2 = 2 • π • R1• CZ1 1 Hz f POLE2 = 2 • π • R • C Z P2 where resistance is in Ohms and capacitance is in Farads. A simple Type I compensation network can be incorporated + ERROR AMP – VOUT 1.22V R1 FB 11 CP1 R2 3533 F05 Figure 5. Error Amplifier with Type I Compensation 14 + ERROR AMP – 1.22V R1 CZ1 FB 12 VC 12 VC VOUT 11 CP1 RZ R2 CP2 3533 F06 Figure 6. Error Amplifier with Type III Compensation 3533fb LTC3533 TYPICAL APPLICATIONS High Efficiency, High Current LED Driver 3.3μH 11 VIN 3V TO 4.2V 10 OFF ON 12 4 7 SW1 SW2 PVIN PVOUT VIN VOUT ILED = 1A 8 4.7μF LTC3533 RUN/SS 9 FB 13 1nF 1 10μF RT VC BURST 44.2k SGND PGND 3 5 6 14 2 100k 95.3k 100k 47pF 301k 3533 TA02 3533fb 15 LTC3533 PACKAGE DESCRIPTION Please refer to http://www.linear.com/product/LTC3533#packaging for the most recent package drawings. DE Package 14-Lead Plastic DFN (4mm × 3mm) (Reference LTC DWG # 05-08-1708 Rev B) 0.70 ±0.05 3.30 ±0.05 3.60 ±0.05 2.20 ±0.05 1.70 ±0.05 PACKAGE OUTLINE 0.25 ±0.05 0.50 BSC 3.00 REF RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 4.00 ±0.10 (2 SIDES) R = 0.05 TYP 3.00 ±0.10 (2 SIDES) R = 0.115 TYP 8 0.40 ±0.10 14 3.30 ±0.10 1.70 ±0.10 PIN 1 NOTCH R = 0.20 OR 0.35 × 45° CHAMFER PIN 1 TOP MARK (SEE NOTE 6) 0.200 REF 0.75 ±0.05 (DE14) DFN 0806 REV B 7 1 0.25 ±0.05 0.50 BSC 3.00 REF 0.00 – 0.05 BOTTOM VIEW—EXPOSED PAD NOTE: 1. DRAWING PROPOSED TO BE MADE VARIATION OF VERSION (WGED-3) IN JEDEC PACKAGE OUTLINE MO-229 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 16 3533fb LTC3533 REVISION HISTORY (Revision history begins at Rev B) REV DATE DESCRIPTION B 01/16 Corrected part number in Order Information PAGE NUMBER 2 Modified Burst Mode Operation 10 Moved application circuit to back page 18 3533fb 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. 17 LTC3533 TYPICAL APPLICATION 1MHz Li-Ion to 3.6V at 2A, Pulsed, with Manual Mode Control 6.8μH 11 VIN 3V TO 4.2V 10 12 OFF ON 1 10μF 4 7 SW1 SW2 PVIN PVOUT VIN VOUT LTC3533 RUN/SS FB RT VC BURST 64.9k SGND PGND 3 5 9 8 388k 220pF 13 14 2.2k VOUT 3.6V AT 2A 15k 470pF 200μF 2 FIXED BURST FREQUENCY 6 200k 3533 TA03 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC3113 3A Low Noise Buck-Boost DC/DC Converter LTC3127 LTC3401/LT3402 1A Buck-Boost DC/DC Converter with Programmable Input Current Limit 1A/2A (ISW), 3MHz Synchronous Step-Up DC/DC Converter LTC3411 1.25A (IOUT), 4MHz Synchronous Step-Up DC/DC Converter LTC3412 2.5A (IOUT), 4MHz Synchronous Step-Up DC/DC Converter LTC3421 3A (ISW), 3MHz Synchronous Step-Up DC/DC Converter LTC3440 600mA (IOUT), 2MHz Synchronous Buck-Boost DC/DC Converter LTC3441 1.2A (IOUT), 1MHz Synchronous Buck-Boost DC/DC Converter LTC3442/LTC3443 LTC3444 1.2A (IOUT), Synchronous Buck-Boost DC/DC Converters, LTC3442 (1MHz), LTC3443 (600kHz) 500mA (IOUT), Synchronous Buck-Boost DC/DC Converter LTC3530 600mA (IOUT), 2MHz Synchronous Buck-Boost DC/DC Converter LTC3532 500mA (IOUT), 2MHz Synchronous Buck-Boost DC/DC Converter LTC3536 1A (IOUT) Low Noise Buck-Boost DC/DC Converter VIN: 1.8V to 5.5V, VOUT: 1.8V to 5.5V, IQ = 300µA, ISD < 1µA, 20-Pin TSSOP Package, 4mm × 5mm DFN VIN: 1.8V to 5.5V, VOUT: 1.8V to 5.25V, IQ = 35µA, ISD < 4mA, 12-Pin MSOP Package, 3mm × 3mm DFN VIN: 0.5V to 5V, VOUT(MAX) = 6V, IQ = 38mA, ISD < 1µA, MS Package VIN: 2.5V to 5.5V, VOUT(MIN) = 0.8V, IQ = 60µA, ISD ≤ 1µA, MS Package VIN: 2.5V to 5.5V, VOUT(MIN) = 0.8V, IQ = 60µA, ISD ≤ 1µA, TSSOP16E Package VIN: 0.5V to 4.5V, VOUT(MAX) = 5.25V, IQ = 12µA, ISD < 1µA, QFN Package VIN: 2.5V to 5.5V, VOUT(MAX): 2.5V to 5.5V, IQ = 25µA, ISD < 1µA, MS, DFN Package VIN: 2.5V to 5.5V, VOUT(MAX): 2.4V to 5.5V, IQ = 25µA, ISD < 1µA, DFN Package VIN: 2.4V to 5.5V, VOUT(MAX): 2.4V to 5.25V, IQ = 28µA, ISD < 1µA, DFN Package VIN: 2.7V to 5.5V, VOUT = 0.5V to 5V, DFN Package, Internal Compensation VIN: 1.8V to 5.5V, VOUT: 1.8V to 5.25V, IQ = 40µA, ISD < 1µA, 10-Pin MSOP Package, 3mm × 3mm DFN VIN: 2.4V to 5.5V, VOUT: 2.4V to 5.5V, IQ = 35µA, ISD < 1µA, 10-Pin MSOP Package, 3mm × 3mm DFN VIN: 1.8V to 5.5V, VOUT: 1.8V to 5.5V, IQ = 32µA, ISD < 1µA, 12-Pin MSOP Package, 3mm × 3mm DFN Thin SOT is a trademark of Linear Technology Corporation. 18 Linear Technology Corporation 3533fb LT 0116 REV B • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com/LTC3533 LINEAR TECHNOLOGY CORPORATION 2007