LTC3127 1A Buck-Boost DC/DC Converter with Programmable Input Current Limit Description Features Programmable (0.2A to 1A) ±4% Accurate Average Input Current Limit n Regulated Output with Input Voltages Above, Below or Equal to the Output n 1.8V to 5.5V (Input) and 1.8V to 5.25V (Output) Voltage Range n 0.6A Continuous Output Current: V > 1.8V IN n 1A Continuous Output Current: V > 3V IN n Single Inductor n Synchronous Rectification: Up to 96% Efficiency n Burst Mode® Operation: I = 35μA (Pin Selectable) Q n Output Disconnect in Shutdown n <1μA Shutdown Current n Small, Thermally Enhanced 10-Lead (3mm × 3mm × 0.75mm) DFN and 12-Lead MSOP Packages n Applications n n n n n The LTC®3127 is a wide VIN range, highly efficient, 1.35MHz fixed frequency buck-boost DC/DC converter that operates from input voltages above, below or equal to the output voltage. The LTC3127 features programmable average input current limit, making it ideal for power-limited input sources. The input current limit is programmed with a single resistor and is accurate from 0.2A to 1A of average input current. The topology incorporated provides a continuous transfer function through all operating modes. Other features include <1μA shutdown current, pin-selectable Burst Mode operation and thermal overload protection. The LTC3127 is housed in thermally enhanced 10-lead (3mm × 3mm × 0.75mm) DFN packages and 12-lead MSOP packages. L, LT, LTC, LTM, Linear Technology, Burst Mode and the Linear logo are registered trademarks and PowerPath and ThinSOT are trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. USB Powered GSM Modems Supercap Charger Handheld Test Instruments PC Card Modems Wireless Terminals Typical Application USB or Li-Ion (500mA Maximum Input Current) to 3.3V Efficiency vs VIN 100 L1 4.7µH 90 SW2 VOUT MODE OFF ON 10µF 320k SHDN FB VC PROG SGND PGND 32.4k 2.2mF 1A LOAD 80 70 182k 100pF 60 499k 3127 TA01 L1: COILCRAFT XPL4020-472ML VOUT 3.3V EFFICIENCY (%) SW1 VIN USB OR Li-Ion 2.9V to 5.5V 300mA LOAD 50 2.5 VOUT = 3.3V L = 4.7µH F = 1.35MHz 3 3.5 4 VIN(V) 4.5 5 5.5 3127 TA01a 3127f LTC3127 Absolute Maximum Ratings (Note 1) VIN , VOUT Voltage .......................................... –0.3 to 6V SW1, SW2 DC Voltage.................................... –0.3 to 6V SW1, SW2 Pulsed (<100ns) Voltage............... –0.3 to 7V MODE, FB, VC Voltage..................................... –0.3 to 6V SHDN Voltage ................................................ –0.3 to 6V PROG Voltage................................................. –0.3 to 6V Operating Junction Temperature Range (Note 2).....................................................–40°C to 85°C Maximum Junction Temperature (Note 5)............ 125°C Storage Temperature Range................... –65°C to 125°C Pin Configuration TOP VIEW TOP VIEW SW1 1 10 SW2 VIN 2 9 VOUT SHDN 3 MODE 4 PROG 5 11 PGND PGND SW1 VIN SHDN MODE PROG 8 VC 7 FB 6 SGND 1 2 3 4 5 6 13 PGND 12 11 10 9 8 7 PGND SW2 VOUT VC FB SGND MSE PACKAGE 12-LEAD PLASTIC MSOP DD PACKAGE 10-LEAD (3mm s 3mm) PLASTIC DFN TJMAX = 125°C, θJA = 43°C/W (NOTE 6) EXPOSED PAD (PIN 11) IS PGND, MUST BE SOLDERED TO PCB TJMAX = 125°C, θJA = 40°C/W (NOTE 6) EXPOSED PAD (PIN 11) IS PGND, MUST BE SOLDERED TO PCB order information LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LTC3127EDD#PBF LTC3127EDD#TRPBF LDYD 10-Lead (3mm × 3mm) Plastic DFN –40°C to 85°C LTC3127EMSE#PBF LTC3127EMSE#TRPBF 3127 12-Lead Plastic MSOP –40°C to 85°C Consult LTC Marketing for parts specified with wider operating temperature ranges. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ 3127f LTC3127 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TJ = 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 l 1.8 5.25 V Feedback Voltage l 1.165 1.195 1.225 V 1 50 nA Feedback Input Current VFB = 1.25V Quiescent Current—Burst Mode Operation VFB > 1.225, VMODE = VIN (Note 4) 35 Quiescent Current—Shutdown VSHDN = 0V, Including SW Leakage 0.1 Quiescent Current—Active VFB > 1.225V, VMODE = 0V (Note 4) 400 Input Current Limit RPROG = 32.4k (Note 3) µA 4 µA µA 480 500 520 mA 0°C to 85°C (Note 3) l 465 500 540 mA –40°C to 85°C (Note 3) l 430 500 540 mA l 2 2.5 0.15 0.3 0.45 A 4 µA Peak Current Limit Reverse-Current Limit A P-Channel MOSFET Leakage Switches A and D 0.1 N-Channel MOSFET On-Resistance Switch B Switch C 140 170 mΩ mΩ P-Channel MOSFET On-Resistance Switch A Switch D 160 190 mΩ mΩ Maximum Duty Cycle Boost( % Switch C On) Buck (% Switch A On) 90 % % l l 80 100 0 Minimum Duty Cycle l Frequency Accuracy l 1 SHDN Input High Voltage l 1.2 SHDN Input Low Voltage SHDN Input Current 0.01 l MODE Input Low Voltage l VMODE = 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. Note 2: The LTC3127 is guaranteed to meet performance specifications from 0°C to 85°C. Specifications over the –40°C to 85°C operating junction temperature range are assured by design, characterization and correlation with statistical process controls. Note that the maximum ambient temperature is determined by specific operating conditions in conjunction with board layout, the rated package thermal resistance and other environmental factors. 1.7 MHz V l VSHDN = 5.5V MODE Input High Voltage MODE Input Current 1.35 % 0.3 V 1 µA 1.2 V 0.01 0.3 V 1 µA Note 3: Specification is guaranteed when the inductor current is in continuous conduction. Note 4: Current measurements are made when the output is not switching. Note 5: This IC includes overtemperature protection that is intended to protect the device during momentary overload conditions. Junction temperature will exceed 125°C when overtemperature protection is active. Continuous operation above the specified maximum operating junction temperature may result in device degradation or failure. Note 6: Failure to solder the exposed backside of the package to the PC board ground plane will result in a thermal resistance much higher than 40°C/W. 3127f LTC3127 Typical Performance Characteristics PWM 90 80 BURST 80 70 70 60 50 40 30 20 VIN = 1.8V VIN = 3.6V VIN = 5V 10 0 0.1 1 10 100 LOAD CURRENT (mA) 50 PWM 40 –2 –3 –4 3.4 3.8 4.2 4.6 VIN (V) VIN = 2.9V VIN = 3.6V VIN = 4.3V 1 10 100 LOAD CURRENT (mA) 5 5.4 VIN = 4.5V VIN = 5V VIN = 5.5V 10 0 0.1 1000 1 10 100 1000 LOAD CURRENT (mA) 3127 G02 10000 3127 G03 Quiescent Current vs VIN (Fixed Frequency Mode–Not Switching) 430 VOUT = 3.3V RPROG = 32.4k 410 0 –1 –2 –3 390 370 350 330 310 290 –5 –45 –30 –15 3127 G04 0 15 30 45 60 TEMPERATURE (°C) 75 90 270 1.8 2.2 2.6 3 3127 G05 3.4 3.8 4.2 4.6 VIN (V) 5 5.4 3127 G06 No Load Input Current vs VIN in Burst Mode Operation 52.5 VOUT = 3.3V 52.0 INPUT CURRENT (µA) 37 INPUT CURRENT (µA) PWM 40 30 Burst Mode Quiescent Current vs VIN 36 35 34 33 32 1.8 2.2 2.6 50 20 –4 38 60 30 1 –1 3 70 20 2 0 –5 1.8 2.2 2.6 60 Average Input Current Limit vs Temperature (Normalized) VOUT = 3.3V RPROG = 32.4k VOUT = 5V 80 BURST 3127 G01 INPUT CURRENT LIMIT (%) INPUT CURRENT LIMIT (%) 1 90 BURST 0 0.1 Average Input Current Limit vs VIN (Normalized) 2 VOUT = 3.3V 10 1000 Efficiency vs Load Current 100 INPUT CURRENT (µA) VOUT = 1.8V EFFICIENCY (%) EFFICIENCY (%) 90 Efficiency vs Load Current 100 EFFICIENCY (%) Efficiency vs Load Current 100 (TJ = 25°C, unless otherwise noted ) 51.5 51.0 50.5 50.0 49.5 49.0 3 3.4 3.8 4.2 4.6 VIN (V) 5 5.4 3127 G07 48.5 1.8 2.2 2.6 3 3.4 3.8 4.2 4.6 VIN (V) 5 5.4 3127 G08 3127f LTC3127 Typical Performance Characteristics Feedback Voltage vs Temperature (Normalized) 0.40 L = 4.7µH VOUT = 3.3V VIN = 3.6V NMOS RDS(ON) vs VIN 300 VOUT = 3.3V 0.30 0.20 –0.20 –0.40 –0.60 250 0.10 RDS(ON) (mΩ) CHANGE (%) 0.00 VOUT Regulation vs Load Current (Normalized) VOUT REGULATION (%) 0.20 (TJ = 25°C, unless otherwise noted ) 0 –0.10 –0.20 –0.30 200 SWC 150 –0.40 SWB –0.50 –0.80 –50 –30 50 –10 10 30 TEMPERATURE (°C) 70 –0.60 90 3127 G09 2250 2000 1750 LOAD CURRENT (mA) 275 RDS(ON) (mΩ) 1000 600 800 400 LOAD CURRENT (mA) 225 SWD 175 2.4 3 1.8 1500 4.2 4.8 5.4 3 3.6 VIN (V) RPROG = 90k 4.8 5.4 3127 G11 ILOAD 1A/DIV VOUT = 2.4V IIN 1A/DIV VOUT 50mV/DIV VOUT = 3.3V 1250 1000 VOUT = 5V 750 IL 1A/DIV 200µs/DIV 0 1.8 2.2 2.6 4.2 Load Transient Response in Fixed Frequency Mode, No Load to 1A, Not in Input Current Limit 250 3.6 VIN (V) 2.4 3127 G10 500 SWA 1.8 100 Maximum Load Current vs VIN PMOS RDS(ON) vs VIN 325 125 200 0 3 3.4 3.8 4.2 4.6 VIN (V) 5 3127 G14 VIN = 3.6V VOUT = 3.3V RPROG = 90k COUT = 4.4mF R3 = 499k C1 = 100pF 5.4 3127 G13 3127 G12 Load Transient Response in Fixed Frequency Mode, No Load to 1A, in Input Current Limit Burst Mode Operation MODE = 0V ILOAD 1A/DIV IL 500mA/DIV IIN 500mA/DIV VOUT 100mV/DIV VOUT 20mV/DIV 200µs/DIV VOUT = 3.3V VIN = 3.6V RPROG = 32.4k COUT = 4.4mF R3 = 499k C1 = 100pF 3127 G15 5µs/DIV 3127 G16 VOUT = 3.3V VIN = 3.6V RPROG = 32.4k COUT = 4.4mF R3 = 499k C1 = 100pF 3127f LTC3127 Typical Performance Characteristics Load Transient Response in Burst Mode Operation, No Load to 1A, Not in Input Current Limit ILOAD 1A/DIV (TJ = 25°C, unless otherwise noted ) Transition from Burst Mode Operation to Fixed Frequency Mode IIN 200mA/DIV IIN 1A/DIV VOUT 50mV/DIV VOUT 20mV/DIV MODE 5V/DIV 200µs/DIV VIN = 3.6V RPROG = 90k R3 = 499k 3127 G17 MODE 5V/DIV 100µs/DIV VOUT = 3.3V COUT = 4.4mF C1 = 100pF 3127 G18 VOUT = 3.3V VIN = 3.6V RPROG = 32.4k COUT = 4.4mF R3 = 499k C1 = 100pF Load Transient Response in Burst Mode Operation, No Load to 1A, in Input Current Limit Start-Up Waveform ILOAD 1A/DIV IIN 500mA/DIV VOUT 100mV/DIV VOUT 1V/DIV IIN 500mA/DIV MODE 5V/DIV SHDN 5V/DIV 200µs/DIV VOUT = 3.3V VIN = 3.6V RPROG = 32.4k COUT = 4.4mF R3 = 499k C1 = 100pF 3127 G19 5ms/DIV 3127 G20 VOUT = 3.3V VIN = 3.6V RPROG = 32.4k COUT = 4.4mF R3 = 499k C1 = 100pF 3127f LTC3127 Pin Functions (DD Package) SW1 (Pin 1): Switch Pin Where Internal Switches A and B Are Connected. Connect inductor from SW1 to SW2. Minimize trace length to reduce EMI. SGND (Pin 6): Signal Ground for the IC. Terminate the PROG resistor, compensation components and the output voltage divider to SGND. VIN (Pin 2): Input Supply Pin. Internal VCC for the IC. A 10μF or greater ceramic capacitor should be placed as close to VIN and PGND as possible. FB (Pin 7): Feedback Pin. Connect resistor divider tap here. The output voltage can be adjusted from 1.8V to 5.25V. The feedback reference voltage is 1.195V. SHDN (Pin 3): Logic-Controlled Shutdown Input. R2 VOUT = 1.195 • 1+ R1 V SHDN = High: Normal Operation SHDN = Low: Shutdown MODE (Pin 4): Pulse Width Modulation/Burst Mode Selection Input. MODE = High: Burst Mode Operation MODE = Low: PWM Operation Only. Forced continuous conduction mode. PROG (Pin 5): Sets the Average Input Current Limit Threshold. Connect a resistor from PROG to ground. See below for component value selection. VC (Pin 8): Error Amplifier Output. Place compensation components from this pin to SGND. VOUT (Pin 9): Output of the Synchronous Rectifier. Connect the output filter capacitor from this pin to GND. A minimum value of 22µF is recommended. Output capacitors must be low ESR. SW2 (Pin 10): Switch Pin Where Internal Switches C and D Are Connected. Minimize trace length to reduce EMI. PGND (Exposed Pad Pin 11): Power Ground. The exposed pad must be soldered to the PCB ground plane. RPROG = 54.92 • ILIMIT (A) + 4.94 (kΩ) 3127f LTC3127 Block Diagram SW1 L SW2 VIN VOUT CIN – + VC IZERO AMP IPEAK AMP PWM COMPARATOR AND LOGIC SHDN MODE PROG RPROG SAMPLE/HOLD AND RESET R2 + – FB + 1.195V – R3 COUT C1 R1 – VCLAMP + SGND 3127 BD 3127f LTC3127 Operation The LTC3127 is an average input current controlled buckboost DC/DC converter offered in both a thermally enhanced 3mm × 3mm DFN package and a thermally enhanced 12lead MSOP package. The buck-boost converter utilizes a proprietary switching algorithm which allows its output voltage to be regulated above, below or equal to the input voltage. The low RDS(ON), low gate charge synchronous switches efficiently provide high frequency PWM control. High efficiency is achieved at light loads when Burst Mode operation is commanded. the AC switch pair remains on for longer durations and the duration of the BD phase decreases proportionally. As the input voltage drops below the output voltage, the AC phase will eventually increase to the point that there is no longer any BD switching. At this point, switch A remains on continuously while switch pair CD is pulse width modulated to obtain the desired output voltage. At this point, the converter is operating solely in boost mode. This switching algorithm provides a seamless transition between operating modes and eliminates discontinuities in average inductor current, inductor current ripple, and loop transfer function throughout all three operational modes. These advantages result in increased efficiency and stability in comparison to the traditional 4-switch buck-boost converter. In forced PWM mode operation, the inductor is forced to have continuous conduction. This allows for a constant switching frequency and better noise performance. PWM Mode Operation The LTC3127 uses fixed frequency, average input current PWM control. The MODE pin can be used to select automatic Burst Mode operation (MODE connected to VIN) or to disable Burst Mode operation and select forced continuous conduction operation for low noise applications (MODE grounded). A proprietary switching algorithm allows the converter to switch between buck, buck-boost and boost modes without discontinuity in inductor current or loop characteristics. The switch topology for the buck-boost converter is shown in Figure 1. Error Amplifier and Compensation The buck-boost converter utilizes two control loops. The outer voltage loop determines the amount of current required to regulate the output voltage. The voltage loop is externally compensated and can be configured with either integral compensation or proportional control. The inner current loop is internally compensated and forces the input current to equal the commanded current. When the input voltage is significantly greater than the output voltage, the buck-boost converter operates in buck mode. Switch D turns on continuously and switch C remains off. Switches A and B are pulse width modulated to produce the required duty cycle to support the output regulation voltage. As the input voltage decreases, switch A remains on for a larger portion of the switching cycle. When the duty cycle reaches approximately 85%, the switch pair AC begins turning on for a small fraction of the switching period. As the input voltage decreases further, When VC is compensated via proportional control, the dominant pole of the output capacitor is used to ensure stability with a minimum of 1000µF of capacitance on the output when a 499k resistor is used. There is no maximum capacitance limitation with proportional compensation. L VIN A SW1 B LTC3127 PGND SW2 D VOUT C PGND 3127 F01 Figure 1. Buck-Boost Switch Topology 3127f LTC3127 Operation Integral compensation is required if an output capacitor less than 1000µF but greater than 44µF is used, otherwise using proportional compensation is recommended. When compensating the converter with integral compensation it is important to consider that the total bandwidth of the network must be below 15kHz. The inner current loop of the LTC3127 eliminates one of the double poles caused by the inductor. The output capacitor causes a dominant pole and also a zero, and the resistor divider sets the gain. GDC = 1 + fPOLE1 = f ZERO1 = R2 R1 1 2 • π • RLOAD • COUT 1 2 • π • RESR • COUT Using the compensation network show in Figure 2, the voltage loop compensation can be approximated with the following transfer function: gm • (C1 • R A • s + 1) H COMP (s) = s • (C1 • C2 • R A • s + C1 + C2) where gm = 150 • 10–6 This causes poles and zeros to occur at the following locations: fPOLE2 @ DC fPOLE3 = 1 2 • π • R A • C2 f ZERO2 = 1 2 • π • R A • C1 The poles and zeros of the compensation should be determined by looking at where fPOLE1 lands at the minimum load where the LTC3127 will be continuously conducting, which places the dominant pole at its lowest frequency. After setting the poles and zeros for the compensation, the phase margin of the system should be greater than 45° and the gain margin should be greater than 3dB. Following these two criteria will help to ensure stability. Current Limit Operation The buck-boost converter has two current limit circuits. The primary current limit is an average input current limit circuit that clamps the output of the outer voltage loop. This limits the amount of input current that can be commanded, and the inner current loop regulates to that clamped value. VOUT VOUT LTC3127 – PWM + MEASURED INPUT CURRENT + – 1.195V R2 FB COUT VC R1 RA C2 SGND C1 3127 F02 Figure 2. Buck-Boost External Compensation 3127f 10 LTC3127 Operation The input current limit is set by the RPROG resistor placed on the PROG pin to SGND. The resistor value can be calculated using the following formula: RPROG = 54.92 • ILIMIT (A) + 4.94 (kΩ) Where ILIMIT is the average input current limit in amps. A secondary 2.5A (typical) current limit forces switches B and D on and A and C off if tripped. This current limit is not affected by the value of RPROG. Reverse Current Limit The reverse current comparator on switch D monitors the inductor current supplied from the output. When this current exceeds 300mA (typical) switch D will be turned off for the remainder of the switching cycle. Burst Mode Operation When the MODE pin is held high the LTC3127 will function in Burst Mode operation as long as the load current is typically less than 35mA. In Burst Mode operation, the LTC3127 still switches at a fixed frequency of 1.35MHz, using the same error amplifiers and loop compensation for average input current mode control. This control method eliminates any output transient when switching between modes. In Burst Mode operation, energy is delivered to the output until the output voltage reaches the nominal regulation value. At this point, the LTC3127 transitions to sleep mode where the output switches are shut off and the LTC3127 consumes only 35μA of quiescent current from VIN . When the output voltage droops slightly, switching resumes. This maximizes efficiency at very light loads by minimizing switching and quiescent losses. Anti-Ringing Control The anti-ringing control connects a resistor from SW1 and SW2 to PGND to prevent high frequency ringing during discontinuous current mode operation in Burst Mode. Although the ringing of the resonant circuit formed by L and CSW (capacitance on SW pin) is low energy, it can cause EMI radiation. Shutdown Shutdown of the converter is accomplished by pulling SHDN below 0.3V and enabled by pulling SHDN above 1.2V. Note that SHDN can be driven above VIN or VOUT, as long as it is limited to less than the absolute maximum rating. Thermal Shutdown If the die temperature exceeds 150°C (typical) the LTC3127 will be disabled. All power devices will be turned off and both switch nodes will be high impedance. The LTC3127 will restart (if enabled) when the die temperature drops to approximately 140°C. Thermal Regulator To help prevent the part from going into thermal shutdown when charging very large capacitive loads, the LTC3127 is equipped with a thermal regulator. If the die temperature exceeds 130°C (typical) the average current limit is lowered to help reduce the amount of power being dissipated in the package. The current limit will be approximately 0A just before thermal shutdown. The current limit will return to its full value when the die temperature drops back below 130°C. Zero Current Comparator Undervoltage Lockout The zero current comparator monitors the inductor current to the output and shuts off the synchronous rectifier when this current reduces to approximately 30mA. This prevents the inductor current from reversing in polarity, improving efficiency at light loads. This comparator is only active in Burst Mode operation. If the input supply voltage drops below 1.7V (typical), the LTC3127 will be disabled and all power devices will be turned off. 3127f 11 LTC3127 Applications Information A typical LTC3127 application circuit is shown on the front page of this data sheet. The external component selection is determined by the desired output voltage, input current and ripple voltage requirements for each particular application. However, basic guidelines and considerations for the design process are provided in this section. Buck-Boost Output Voltage Programming The buck-boost output voltage is set by a resistive divider according to the following formula: R2 VOUT = 1.195V • 1 + V R1 The external divider is connected to the output as shown in Figure 3. The buck-boost converter utilizes input current mode control, and the output divider resistance does not play a role in the stability. 1.8V b VOUT b 5.25V R2 FB LTC3127 R1 GND 3127 F03 Figure 3. Setting the Buck-Boost Output Voltage The LTC3127 can utilize small surface mount inductors due to its fast 1.35MHz switching frequency. Inductor values between 2.2μH and 4.7μH are suitable for most applications. Larger values of inductance will allow slightly greater output current capability by reducing the inductor ripple current. Increasing the inductance above 10μH will increase size while providing little improvement in output current capability. The inductor current ripple is typically set for 20% to 40% of the maximum inductor current. High frequency ferrite core inductor materials reduce frequency dependent power losses compared to cheaper powdered iron types, improving efficiency. The inductor should have low ESR (series resistance of the windings) to reduce the I2R power losses, and must be able to support the peak inductor current without saturating. Molded chokes and some chip inductors usually do not have enough core area to support the peak inductor currents of 2.5A seen on the LTC3127. To minimize radiated noise, use a shielded inductor. See Table 1 and the reference schematics for suggested components and suppliers. Table 1. Recommended Inductors VENDOR PART/STYLE Coilcraft 847-639-6400 www.coilcraft.com LPO2506 LPS4012, LPS4018 MSS6122 MSS4020 MOS6020 DS1605, DO1608 XPL4020 Coiltronics www.cooperet.com SD52, SD53 SD3114, SD3118 Murata 714-852-2001 www.murata.com LQH55D Sumida 847-956-0666 www.sumida.com CDH40D11 Taiyo-Yuden www.t-yuden.com NP04SB NR3015 NR4018 TDK 847-803-6100 www.component.tdk.com VLP, LTF VLF, VLCF Würth Elektronik 201-785-8800 www.we-online.com WE-TPC Type S, M, MH Buck-Boost Inductor Selection To achieve high efficiency, a low ESR inductor should be utilized for the buck-boost converter. The inductor must have a saturation rating greater than the worst case average inductor current plus half the ripple current. The peak-to-peak inductor current ripple will be larger in buck and boost mode than in the buck-boost region. The peak-to-peak inductor current ripple for each mode can be calculated from the following formulas, where L is the inductance in μH: V ( V − VOUT ) ∆ I L,P −P,BUCK = OUT IN ( A) VIN • L • (1.35MHz) ∆ I L,P −P,BOOST VIN ( VOUT − VIN ) = ( A) VOUT • L • (1.35MHz) 3127f 12 LTC3127 Applications Information Output and Input Capacitor Selection The total output voltage droop is given by: When selecting output capacitors for large pulsed loads, the magnitude and duration of the pulse current, together with the droop voltage specification, determine the choice of the output capacitor. Both the ESR of the capacitor and the charge stored in the capacitor each cycle contribute to the output voltage droop. The droop due to the charge is approximately: VDROOP = VDROOP_LOAD + VDROOP_ESR (V) V DROOP _ LOAD = VIN • IIN(MAX ) • h − ISTANDBY • D • T I PULSE − VOUT ( V) COUT where IPULSE = pulsed load current ISTANDBY = static load current in standby mode IIN(MAX) = programmed input current limit in amps T = period of the load pulse High capacitance values and low ESR can lead to instability in typical internally compensated buck-boost converters. Using proportional compensation, the LTC3127 is stable with low ESR output capacitor values greater than 1000µF. Multilayer ceramic capacitors are an excellent choice for input decoupling of the step-up converter as they have extremely low ESR and are available in small footprints. Input capacitors should be located as close as possible to the device. While a 10µF input capacitor is sufficient for most applications, larger values may be used to improve input decoupling without limitation. Consult the manufacturers directly for detailed information on their selection of ceramic capacitors. Although ceramic capacitors are recommended, low ESR tantalum capacitors may be used as well. When using a large capacitance to help with pulsed load applications, the maximum load for a given duty cycle, and the minimum capacitance can be calculated by: D = load pulse’s duty cycle VDROOP = amount the output falls out of regulation in volts I LOAD(MAX ) = h = the efficiency of the converter at the input current limit point C OUT(MIN) = The preceding equation is a worst-case approximation assuming all the pulsing energy comes from the output capacitor. VIN • IIN(MAX ) • h = I PULSE − − ISTANDBY • ESR ( V) VOUT Low ESR and high capacitance are critical to maintaining low output droop. Table 2 and the Typical Applications schematics show a list of several reservoir capacitor manufacturers. D • VOUT ( A) VIN • IIN(MAX ) • h − ISTANDBY IPULSE − VOUT The droop due to the capacitor equivalent series resistance (ESR) is: V DROOP _ ESR VIN • IIN(MAX ) • h • D•T (F) VDROOP Table 2. Capacitor Vendor Information SUPPLIER PHONE WEB SITE Vishay 402-563-6866 www.vishay.com AVX 803-448-9411 www.avxcorp.com Cooper Bussmann 516-998-4100 www.cooperbussmann.com CAP-XX 843-267-0720 www.cap-xx.com Panasonic 800-394-2112 www.panasonic.com 3127f 13 LTC3127 Applications Information Capacitor Selection Example In this example, a pulsed load application requires that VOUT droops less than 300mV. The application is a Li-Ion battery input to a 3.6V output. The pulsed load is a no-load to a 1.5A step with a frequency of 217Hz and a duty cycle of 12.5%. The input current limit is set to 500mA. In order to meet the 300mV droop requirement, the amount of capacitance must be calculated at the highest VIN to VOUT step-up ratio. All of the following calculations assume a minimum VIN of 3V and an efficiency of 90%. Given the application, the following is known: VIN = 3V Step 2: Calculate the minimum output capacitance required. 3V • 500mA • 0 . 9 COUT(MIN) ≥ 1 . 5A − 3 . 6V • 0 . 125 • 4 . 6ms = 2 . 15mF 300mV Step 3: For this application a 2.2mF Vishay Tantamount tantalum, low ESR capacitor is selected. This capacitor has a maximum ESR of 0.04Ω. With the selected capacitor, the amount of droop must be calculated: VDROOP _ LOAD = VOUT = 3.6V 3V • 500mA • 0 . 9 − 0 A • 0 . 125 • 4 . 6ms 1 . 5 A − 3 . 6V 2 . 2mF = 0 . 294V IIN(MAX) = 500mA IPULSE = 1.5A ISTANDBY = 0A h = 0.9 D = 0.125 VDROOP _ ESR = T = 1/217Hz = 4.6ms 3V • 500mA • 0 . 9 − 0 A • 0 . 04Ω 1 . 5 A − 3 . 6V = 0 . 045V VDROOP = 300mV Step 1: Check to make sure the application can provide enough current to recover from the pulsed load using the ILOAD(MAX) equation: ILOAD(MAX ) = 3V • 500mA • 0 . 9 = 3A 0 . 125 • 3 . 6 V The maximum load that can be pulsed at this VIN to VOUT combination is 3A. VDROOP = VDROOP _ LOAD + VDROOP _ ESR = 0 . 339 V Due to the ESR of the capacitor, the total droop is greater than 300mV. In this case, if the higher droop cannot be accepted, a larger valued, lower ESR capacitor can be selected. 3127f 14 LTC3127 Applications Information PCB Layout Considerations The LTC3127 switches large currents at high frequencies. Special care should be given to the PCB layout to ensure stable, noise-free operation. Figure 4 depicts the recommended PCB layout to be utilized for the LTC3127. A few key guidelines follow: 1. All circulating high current paths should be kept as short as possible. This can be accomplished by keeping the routes to all bold components in Figure 4 as short and as wide as possible. Capacitor ground connections should via down to the ground plane in the shortest route possible. The bypass capacitor on VIN should be placed as close to the IC as possible and should have the shortest possible path to ground. 2. The small-signal ground pad (SGND) should have a single point connection to the power ground. A con- VIA TO GROUND SW1 venient way to achieve this is to short the pin directly to the Exposed Pad as shown in Figure 4. 3. The components shown in bold and their connections should all be placed over a complete ground plane. 4. To prevent large circulating currents from disrupting the output voltage sensing, the ground for the resistor divider and RPROG should be returned directly to the small signal ground pin (SGND). 5. Use of vias in the die attach pad will enhance the thermal environment of the converter especially if the vias extend to a ground plane region on the exposed bottom surface of the PCB. 6. Keep the connections to the FB and PROG pins as short as possible and away from the switch pin connections. VIA TO GROUND SW2 1 10 VIN 2 9 SHDN 3 MODE 4 PROG 5 PGND 8 7 VOUT VC FB 6 SGND 3127 F04 Figure 4. Recommended PCB Layout 3127f 15 LTC3127 Typical Applications USB (500mA Max), 3.8V GSM Pulsed Load L1 4.7µH SW1 VIN VIN USB SW2 VOUT VOUT 3.8V MODE PWM BURST 2.15M LTC3127 OFF ON FB SHDN 10µF C2 2.2mF 1M VC PROG SGND PGND 100pF 32.4k C1, C2: VISHAY TANTAMOUNT TANTALUM, LOW ESR CAPACITORS L1: COILCRAFT XPL4020-472ML C1 2.2mF 499k 3127 TA02 PCMCIA/Compact Flash (3.3V or 5V/500mA Max), 3.8V GPRS, Class 10 Pulsed Load L1 4.7µH SW1 VIN VIN 3.3V OR 5V SW2 VOUT 2.15M MODE PWM BURST LTC3127 OFF ON SHDN 10µF PROG SGND C1, C2, C3: VISHAY TANTAMOUNT TANTALUM, LOW ESR CAPACITORS L1: COILCRAFT XPL4020-472ML VOUT 3.8V 32.4k FB VC PGND 100pF C3 2.2mF 1M 499k C2 2.2mF C1 2.2mF 3127 TA03 3127f 16 LTC3127 Typical Applications Stacked Supercapacitor Charger (1000mA Max Input Current) L1 4.7µH VIN 1.8V to 5.5V SW1 VIN PWM BURST MODE SW2 VOUT 3.16M LTC3127 FB SHDN OFF ON VC PROG 10µF VOUT 5V SGND 1M 100k C2 100F PGND 100pF 60.4k 100k C1 100F 499k L1: COILCRAFT XPL4020-472ML 3127 TA04 General Purpose Forced Continuous Conduction Application with 500µs Start-Up L1 4.7µH SW1 VIN VIN 3V TO 4.3V SW2 VOUT VOUT 3.3V 316k 33pF MODE PWM BURST FB SHDN OFF ON PROG SGND 10µF 0.01µF L1: COILCRAFT XPL4020-472ML LTC3127 60.4k PGND VC 47k 22µF s2 182k 3300pF 3127 TA05 3127f 17 LTC3127 Package Description DD Package 10-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1699 Rev B) 0.70 p0.05 3.55 p0.05 1.65 p0.05 2.15 p0.05 (2 SIDES) PACKAGE OUTLINE 0.25 p 0.05 0.50 BSC 2.38 p0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 3.00 p0.10 (4 SIDES) R = 0.125 TYP 6 0.40 p 0.10 10 1.65 p 0.10 (2 SIDES) PIN 1 TOP MARK (SEE NOTE 6) 0.200 REF 0.75 p0.05 0.00 – 0.05 5 1 (DD) DFN REV B 0309 0.25 p 0.05 0.50 BSC 2.38 p0.10 (2 SIDES) BOTTOM VIEW—EXPOSED PAD NOTE: 1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2). CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT 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 3127f 18 LTC3127 Package Description MSE Package 12-Lead Plastic MSOP, Exposed Die Pad (Reference LTC DWG # 05-08-1666 Rev B) BOTTOM VIEW OF EXPOSED PAD OPTION 2.845 p 0.102 (.112 p .004) 5.23 (.206) MIN 2.845 p 0.102 (.112 p .004) 0.889 p 0.127 (.035 p .005) 6 1 1.651 p 0.102 3.20 – 3.45 (.065 p .004) (.126 – .136) 0.12 REF 12 0.65 0.42 p 0.038 (.0256) (.0165 p .0015) BSC TYP RECOMMENDED SOLDER PAD LAYOUT 0.254 (.010) 0.35 REF 4.039 p 0.102 (.159 p .004) (NOTE 3) DETAIL “B” CORNER TAIL IS PART OF DETAIL “B” THE LEADFRAME FEATURE. FOR REFERENCE ONLY 7 NO MEASUREMENT PURPOSE 0.406 p 0.076 (.016 p .003) REF 12 11 10 9 8 7 DETAIL “A” 0o – 6o TYP 3.00 p 0.102 (.118 p .004) (NOTE 4) 4.90 p 0.152 (.193 p .006) GAUGE PLANE 0.53 p 0.152 (.021 p .006) DETAIL “A” 1.10 (.043) MAX 0.18 (.007) SEATING PLANE 0.22 – 0.38 (.009 – .015) TYP 1 2 3 4 5 6 0.650 (.0256) BSC NOTE: 1. DIMENSIONS IN MILLIMETER/(INCH) 2. DRAWING NOT TO SCALE 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX 0.86 (.034) REF 0.1016 p 0.0508 (.004 p .002) MSOP (MSE12) 0608 REV B 3127f 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 LTC3127 Typical Application Single Supercapacitor Charger (1000mA Max Input Current) L1 4.7µH SW1 VIN VIN 1.8V TO 5V SW2 VOUT VOUT 2.5V 1.05M MODE PWM BURST LTC3127 SHDN OFF ON PROG 10µF SGND C1: COOPER BUSSMANN POWERSTOR B-SERIES, B1860-2R5107-R L1: COILCRAFT XPL4020-472ML PGND 60.4k FB 1M VC 100pF C1 100F 499k 3127 TA06 Related Parts PART NUMBER DESCRIPTION COMMENTS LTC3101 Wide VIN, 1MHz Multioutput DC/DC Converter and PowerPath™ Controller 95% Efficiency, VIN: 1.8V to 5.5V, VOUT(MAX): 1.8V to 5.25V, IQ = 35µA, ISD < 1µA, 4mm × 4mm QFN-24 Package LTC3125 1.2A IOUT, 1.6MHz, Synchronous Boost DC/DC Converter With Adjustable Input Current Limit 94% Efficiency, VIN: 1.8V to 5.5V, VOUT(MAX) = 5.25V, IQ = 15µA, ISD < 1µA, 2mm × 3mm DFN-8 Package LTC3606B 800mA IOUT, Synchronous Step-Down DC/DC Converter with Average Input Current Limit 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MAX) = 0.6V, IQ = 420µA, ISD < 1µA, 3mm × 3mm DFN-8 Package LTC3440 600mA IOUT, 2MHz, Synchronous Buck-Boost DC/DC Converter 95% Efficiency, VIN: 2.5V to 5.5V, VOUT: 2.5V to 5.5V, IQ = 25µA, ISD < 1µA, 3mm × 3mm DFN-10 and MSOP-10 Packages LTC3441/LTC3441-2/ LTC3441-3 1.2A IOUT, 2MHz, Synchronous Buck-Boost DC/DC Converter 95% Efficiency, VIN: 2.4V to 5.5V, VOUT: 2.4V to 5.25V, IQ = 50µA, ISD < 1µA, 3mm × 4mm DFN-12 Package LTC3520 1A 2MHz, Synchronous Buck-Boost and 600mA Buck Converter 95% Efficiency, VIN: 2.2V to 5.5V, VOUT(MAX) = 5.25V, IQ = 55µA, ISD < 1µA, 4mm × 4mm QFN-24 Package LTC3530 600mA IOUT, 2MHz, Synchronous Buck-Boost DC/DC Converter 95% Efficiency, VIN: 1.8V to 5.5V, VOUT: 1.8V to 5.25V, IQ = 40µA, ISD < 1µA, 3mm × 3mm DFN-10 and MSOP-10 Packages LTC3532 500mA IOUT, 2MHz, Synchronous Buck-Boost DC/DC Converter 95% Efficiency, VIN: 2.4V to 5.5V, VOUT: 2.4V to 5.25V, IQ = 35µA, ISD < 1µA, 3mm × 3mm DFN-10 and MSOP-10 Packages LTC3533 2A IOUT, 2MHz, Synchronous Buck-Boost DC/DC Converter 95% Efficiency, VIN: 1.8V to 5.5V, VOUT: 1.8V to 5.25V, IQ = 40µA, ISD < 1µA, 3mm × 4mm DFN-14 Package LTC3538 800mA IOUT, 1MHz, Synchronous Buck-Boost DC/DC Converter 95% Efficiency, VIN: 2.4V to 5.5V, VOUT: 1.8V to 5.25V, IQ = 35µA, ISD < 1µA, 2mm × 3mm DFN-8 Package LTC3534 500mA IOUT, 1MHz, Synchronous Buck-Boost DC/DC Converter 95% Efficiency, VIN: 2.4V to 7V, VOUT: 1.8V to 2V, IQ = 25µA, ISD < 1µA, 3mm × 3mm DFN-16 and SSOP-16 Packages 3127f 20 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com LT 0210 • PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 2010