LTC3100 1.5MHz Synchronous Dual Channel DC/DC Converter and 100mA LDO DESCRIPTION FEATURES n n n n n n n n Extremely Compact Triple-Rail Solution Burst Mode® Operation, IQ = 15μA 1.5MHz Fixed Frequency Operation Power Good Indicators 700mA Synchronous Step-Up DC/DC 0.65V to 5V VIN Range 1.5V to 5.25V VOUT Range 94% Peak Efficiency VIN > VOUT Operation Output Disconnect 250mA Synchronous Step-Down DC/DC 1.8V to 5.5V VIN Range 0.6V to 5.5V VOUT Range LDO (VIN Internally Tied to VBST) 0.6V to 5.25V VOUT Range 200mV Dropout Voltage at 100mA Available in a 16-Lead 3mm × 3mm QFN Package n n A switching frequency of 1.5MHz minimizes solution footprint by allowing the use of tiny, low profile inductors and ceramic capacitors. The switching regulators use current mode control and are internally compensated, reducing external parts count. Each converter automatically transitions to Burst Mode operation to maintain high efficiency over the full load range. Burst Mode operation can be disabled for low noise applications. The integrated LDO provides a third low noise, low dropout supply. Anti-ringing circuitry reduces EMI by damping the boost inductor in discontinuous mode. Additional features include shutdown current of under 1μA and overtemperature shutdown. The LTC3100 is housed in a 16-lead 3mm × 3mm 0.75mm QFN package. APPLICATIONS n The LTC®3100 combines a high efficiency 700mA synchronous step-up converter, a 250mA synchronous step-down converter and a 100mA LDO regulator. The LTC3100 features a wide input voltage range of 0.65V to 5V. The step-down converter can be powered by the output of the step-up converter or from a separate power source between 1.8V and 5.5V. The LDO can also be used as a sequencing switch on the output of the boost. Bar Code Readers Medical Instruments Low Power Portable Electronic Devices , LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. TYPICAL APPLICATION Efficiency and Power Loss vs Load Current, VIN = 2.4V Two-Cell, Triple Output Converter 3.3μH SWBST VINBK VINBST 1.87M VBST 10μF s2 80 BOOST_GOOD 3V AT 50mA VLDO PGBST VLDO 102k 2.2μF FBLDO 1.8V AT 200mA VBUCK 4.7μH BOOST LDO OFF ON RUNBST OFF ON RUNLDO OFF ON RUNBK SWBK 2M FBBK 1M BUCK GND 10μF 10 50 40 1 BOOST BUCK PL, BOOST PL, BUCK 20 10 0 0.01 1M 0.1 1 10 100 LOAD CURRENT (mA) 0.1 0.01 1000 3100 TA01b PGBK 3100 TA01a 60 30 25.5k MODE 100 70 POWER LOSS (mW) 1.07M LTC3100 1000 90 FBBST 2.2μF FF EN_BURST 100 1M EFFICIENCY (%) VBATT 1.6V TO 3.2V 3.3V AT 100mA VBOOST BUCK_GOOD 3100fa 1 LTC3100 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) MODE RUNBST VINBST PGBST TOP VIEW VINBST and VINBK Voltage .............................. –0.3 to 6V SWBST, SWBK DC Voltage ............................. –0.3 to 6V SWBST, SWBK Pulsed (< 100ns) Voltage ...... –0.3 to 7V FBBST, FBBK, FBLDO, PGBST, PGBK Voltage . –0.3 to 6V MODE, RUNBST, RUNBK, RUNLDO Voltage ... –0.3 to 6V VBST, VLDO ...................................................... –0.3 to 6V Operating Temperature (Notes 2, 5) .........–40°C to 85°C Storage Temperature Range...................–65°C to 125°C 16 15 14 13 SWBST 1 12 FBBST VBST 2 11 FBLDO 17 VLDO 3 10 RUNLDO SWBK 4 6 7 8 VINBK PGBK GND RUNBK 9 5 FBBK UD PACKAGE 16-LEAD (3mm s 3mm) PLASTIC QFN TJMAX = 125°C, θJA = 68°C/W, 4-LAYER BOARD EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB (NOTE 6) ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LTC3100EUD#PBF LTC3100EUD#TRPBF LDJR 16-Lead (3mm × 3mm) Plastic QFN –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/ ELECTRICAL CHARACTERISTICS: STEP-UP CONVERTER The l denotes the specifications which apply over the full operating temperature range. Extended commercial grade: –40°C to 85°C, VINBST = 1.2V, VBST = 3.3V, TA = 25°C, unless otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS Minimum Start-Up Voltage ILOAD = 1mA l 0.65 0.90 V Input Voltage Range After Start-Up (Minimum Voltage Is Load Dependent) l 0.5 5 V Output Voltage Adjust Range l 1.5 5.25 V l Feedback Voltage 1.182 1.200 1.218 V 1 50 nA RUNBST = 0V, Not Including Switch Leakage, VBST = 0V, VINBK = 0V 0.01 1 μA Quiescent Current: Active Measured on VBST (Note 4), RUNBK = 0V, RUNLDO = 0V 300 500 μA Quiescent Current: Burst Mode Operation Measured on VBST, FBBST > 1.25V MODE = 1V, RUNLDO = 0V MODE = 1V, RUNLDO = 1V 15 28 25 45 μA μA N-Channel MOSFET Switch Leakage Current SWBST = 5V, VBST= 5V 0.1 5 μA P-Channel MOSFET Switch Leakage Current SWBST = 0V, VBST = 5V 0.1 10 μA Feedback Input Current FBBST = 1.2V Quiescent Current (VIN): Shutdown 3100fa 2 LTC3100 ELECTRICAL CHARACTERISTICS: STEP-UP CONVERTER The l denotes the specifications which apply over the full operating temperature range. Extended commercial grade: –40°C to 85°C, VINBST = 1.2V, VBST = 3.3V, TA = 25°C, unless otherwise noted. PARAMETER CONDITIONS N-Channel MOSFET Switch-On Resistance VBST = 3.3V 0.3 Ω P-Channel MOSFET Switch-On Resistance VBST = 3.3V 0.4 Ω N-Channel MOSFET Current Limit MIN MAX UNITS l 700 850 mA 87 90 % Maximum Duty Cycle VFBBST = 1.15V l Minimum Duty Cycle VFBBST = 1.3V l 0 Switching Frequency l 1.2 RUNBST Input High Voltage l 0.9 RUNBST Input Low Voltage l RUNBST Input Current TYP RUNBST = 1.2V 1.5 MHz V 0.8 Soft-Start Time 1.8 % 0.3 V 2 μA 0.8 ms PGBST Threshold, Falling Referenced to Feedback Voltage –8 % PGBST Hysteresis Referenced to Feedback Voltage 3 % PGBST Voltage Low 5mA Load 65 mV PGBST Leakage Current PGBST = 5.5V 0.01 10 μA ELECTRICAL CHARACTERISTICS: STEP-DOWN CONVERTER The l denotes the specifications which apply over the full operating temperature range. Extended commercial grade: –40°C to 85°C, VINBK = 3.3V, TA = 25°C, unless otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS Input Voltage Range l 1.8 5.5 V Output Voltage Adjust Range l 0.61 5.5 V Feedback Voltage l 590 600 610 mV Feedback Input Current FBBK = 600mV 1 30 nA Quiescent Current: Shutdown Measured on VINBK, RUNBK = 0V, VINBST = 0V, VBST = 0V Not Including Switch Leakage 0.01 1 μA Quiescent Current: Active Measured on VINBK (Note 4), RUNBST = 0V 240 350 μA Quiescent Current: Burst Mode Operation Measured on VINBK, FBBK = 620mV, MODE = OPEN, RUNBST = 0V 16 30 μA N-Channel MOSFET Switch Leakage Current VINBK = SWBK = 5V 0.1 5 μA P-Channel MOSFET Switch Leakage Current SWBK = 0V, VINBK = 5V 0.1 5 μA N-Channel MOSFET Switch-On Resistance VINBK = 3.3V 0.45 Ω P-Channel MOSFET Switch-On Resistance VINBK = 3.3V 0.55 Ω 450 mA P-Channel MOSFET Current Limit l 340 Maximum Duty Cycle FBBK < 590mV l 100 Minimum Duty Cycle FBBK > 610mV l Switching Frequency l % 0 1.2 1.5 1.8 % MHz 3100fa 3 LTC3100 ELECTRICAL CHARACTERISTICS: STEP-DOWN CONVERTER The l denotes the specifications which apply over the full operating temperature range. Extended commercial grade: –40°C to 85°C, VINBK = 3.3V, TA = 25°C, unless otherwise noted. PARAMETER CONDITIONS MIN RUNBK Input High Voltage l RUNBK Input Low Voltage l RUNBK Input Current TYP MAX 0.9 V 0.8 RUNBK = 1.2V Soft-Start Time UNITS 0.3 V 2 μA 1.3 ms PGBK Threshold, Falling Referenced to Feedback Voltage –8 % PGBK Hysteresis Referenced to Feedback Voltage 3 % PGBK Voltage Low 5mA Load 65 mV PGBK Leakage Current PGBK = 5.5V 0.01 10 μA ELECTRICAL CHARACTERISTICS: LDO REGULATOR The l denotes the specifications which apply over the full operating temperature range. Extended commercial grade: –40°C to 85°C, VBST = 3.3V, VLDO = 3V, TA = 25°C, unless otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS 1.8 5.25 V 0.618 5.25 V 618 mV l l Feedback Voltage l 582 600 Maximum Output Current l 100 120 Input Voltage Range Output Voltage Adjust Range Feedback Input Current (Note 3) FBLDO = 600mV 1 mA 30 nA Line Regulation VIN = 3.3V to 5.25V 0.1 %/ V Load Regulation From 10mA to 100mA Load 0.1 % Dropout Voltage IOUT = 100mA Ripple Rejection (PSRR) Frequency = 1.5MHz at ILOAD = 50mA, COUT = 2.2μF (Note 3) Short-Circuit Current Limit FBLDO < 582mV l 130 200 35 l 120 Soft-Start Time dB 160 0.3 RUNLDO Input High Voltage l RUNLDO Input Low Voltage l mV mA ms 0.9 V 0.3 V RUNLDO Input Current RUNLDO = 1.2V 0.8 2 μA Quiescent Current—Active RUNLDO = 3.3V, Measured on VBST RUNBST = RUNBK = 0V, VINBK = 0V 26 40 μA ELECTRICAL CHARACTERISTICS: COMMON CIRCUITRY The l denotes the specifications which apply over the full operating temperature range. Extended commercial grade: –40°C to 85°C, VBST or VINBK = 3.3V, TA = 25°C, unless otherwise noted. PARAMETER CONDITIONS MIN MODE Input High Voltage l MODE Input Low Voltage l MODE Input Current MODE = 0V MODE = 5V TYP MAX 0.9 UNITS V –3.3 1.7 0.3 V –5 3 μA μA 3100fa 4 LTC3100 ELECTRICAL CHARACTERISTICS 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 LTC3100E is guaranteed to meet performance specifications from 0°C to 85°C. Specifications over –40°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical process controls. Note 3: Specification is guaranteed by design and not 100% tested in production. 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 68°C/W. TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise specified. Step-Up DC/DC Converter Efficiency vs Load Current and VIN for VO = 1.8V Efficiency vs Load Current and VIN for VO = 3.3V 100 90 90 80 10 50 40 1 30 VIN = 1.2V VIN = 1.5V PL, VIN = 1.2V PL, VIN = 1.5V 20 10 0 0.01 0.1 1 10 100 LOAD CURRENT (mA) EFFICIENCY (%) 60 70 10 60 50 1 40 VIN = 1.2V VIN = 2.4V VIN = 3V PL, VIN = 1.2V PL, VIN = 2.4V PL, VIN = 3V 30 20 0.1 10 0 0.01 0.01 1000 0.1 1 10 100 LOAD CURRENT (mA) Efficiency vs Load Current and VIN for VO = 5V 0.01 1000 3.3V, 100mA Efficiency vs VIN 100 1000 100 100 80 90 60 10 50 40 1 VIN = 1.8V VIN = 2.4V VIN = 3.6V PL, VIN = 1.8V PL, VIN = 2.4V PL, VIN = 3.6V 30 20 10 0.1 1 10 100 LOAD CURRENT (mA) POWER LOSS (mW) 70 0.1 0.01 1000 3100 G03 EFFICIENCY (%) 90 80 EFFICIENCY (%) 0.1 3100 G02 3100 G01 0 0.01 POWER LOSS (mW) 70 100 80 100 POWER LOSS (mW) EFFICIENCY (%) 1000 100 1000 70 60 50 40 30 20 10 VBST = 3.3V AT 100mA 0 1.8 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4 4.2 VINBST (V) 3100 G04 3100fa 5 LTC3100 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise specified. Step-Up DC/DC Converter No-Load Input Current vs VIN, Mode = Open, LDO and Buck Off 600 180 160 1000 VOUT = 3.3V 500 120 100 80 60 VOUT = 5V 40 VOUT = 1.8V LOAD CURRENT (mA) OUTPUT CURRENT (mA) 140 INPUT CURRENT (μA) Maximum Load Current During Start-Up vs VIN Maximum Output Current vs VIN 400 300 VOUT = 5V 200 100 10 100 20 VOUT = 1.8V VOUT = 3.3V 0 0 1.0 1.5 2.0 2.5 3.0 VINBST (V) 3.5 4.0 0 4.5 0.5 1 1.5 2 2.5 3 VINBST (V) Burst Mode Threshold Current vs VIN 1 4.5 0.7 0.8 0.9 1 1.1 VINBST (V) 1.2 1.3 3100 G07 VBST = 1.8V, RESISTIVE LOAD VBST = 1.8V, CONSTANT-CURRENT LOAD VBST = 3.3V, RESISTIVE LOAD VBST = 3.3V, CONSTANT-CURRENT LOAD VBST = 5V, RESISTIVE LOAD VBST = 5V, CONSTANT-CURRENT LOAD Start-Up Voltage vs Temperature 0.85 L = 3.3μH 0.80 40 INPUT VOLTAGE (V) 50 LOAD CURRENT (mA) 4 3100 G06 3100 G05 60 3.5 VOUT = 3.3V VOUT = 1.8V 30 VOUT = 5V 20 10 0.75 0.70 0.65 0.60 0.55 0 1.0 1.5 2.0 2.5 3.0 VINBST (V) 3.5 4.0 4.5 0.50 –45 –30 –15 0 15 30 45 60 TEMPERATURE (°C) 75 90 3100 G09 3100 G08 Output Voltage Ripple in Fixed Frequency and Burst Mode Operation VOUT and IIN During Soft-Start VBST COUT = 20μF 0.5μs/DIV 100mA LOAD 20mV/DIV IIN 200mA/DIV 20μs/DIV 5mA LOAD 20mV/DIV VBST 1V/DIV 500μs/DIV 3100 G10 3100 G11 3100fa 6 LTC3100 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise specified. Step-Up DC/DC Converter Load Step Response, 50mA-150mA Fixed Frequency Mode Load Step Response, 5mA-100mA Burst Mode Operation Enabled VBST COUT = 10μF VBST COUT = 20μF IOUT 100mA/DIV IOUT 100mA/DIV VBST 50mV/DIV VBST 50mV/DIV 3100 G12 100μs/DIV 100μs/DIV 3100 G13 LDO Regulator Dropout Voltage vs VOUT and Temperature (IOUT = 100mA) Ripple Rejection VLDO = 1.5V 0.225 LDO COUT = 2.2μF 35 0.200 30 0.175 VLDO = 2.5V 0.150 0.125 RUNLDO 2V/DIV 25 20 15 VLDO 1V/DIV VLDO = 5V 0.100 0.075 Soft-Start Time 40 PSRR (dB) DROPOUT VOLTAGE (VBST_VLDO) 0.250 10 VLDO = 3.3V 0.050 –45 –30 –15 0 15 30 45 60 90 75 VOUT = 3V 5 I OUT = 50mA COUT = 2.2μF 0 0.1 1 TEMPERATURE (°C) 100μs/DIV 10 100 FREQUENCY (Hz) 1000 6105 G14 10000 3100 G15 Burst Mode Operation Ripple Rejection Load Step Response, 10mA-60mA LDO COUT = 2.2μF LDO COUT = 2.2μF BOOST RIPPLE 20mV/DIV 50mA/DIV LDO RIPPLE 20mV/DIV VLDO 100mV/DIV 5μs/DIV 3100 G16 3100 G17 200μs/DIV 3100 G18 3100fa 7 LTC3100 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise specified. Step-Down DC/DC Converter Efficiency vs Load Current and VIN for VO = 1.2V 100 Efficiency vs Load Current and VIN for VO = 1.8V 90 90 80 50 40 1 VIN = 1.8V VIN = 2.4V VIN = 3.3V PL, VIN = 1.8V PL, VIN = 2.4V PL, VIN = 3.3V 30 20 10 0 0.01 0.1 EFFICIENCY (%) 10 70 50 1 40 VIN = 2.4V VIN = 3.3V VIN = 5V PL, VIN = 2.4V PL, VIN = 3.3V PL, VIN = 5V 30 20 0.1 10 0 0.01 0.01 1000 1 10 100 LOAD CURRENT (mA) 10 60 0.1 1 10 100 LOAD CURRENT (mA) Burst Mode Operation Threshold Current vs VIN 20 LOAD CURRENT (mA) INPUT CURRENT (μA) 70 10 5 VOUT = 1.2V INPUT CURRENT 50mA/DIV 50 VOUT = 1.5V 30 VOUT 0.5V/DIV 20 VOUT = 1.8V 10 0 1.5 2 2.5 3 3.5 4 4.5 STARTUP, 200mA LOAD VIN = 2.4V VOUT = 1.2V COUT = 10μF 60 40 0.01 1000 VOUT and IIN During Soft-Start 80 15 0.1 3100 G20 3100 G19 No-Load Input Current vs VINBK (Mode = Open) POWER LOSS (mW) 60 100 80 100 70 POWER LOSS (mW) EFFICIENCY (%) 1000 100 1000 VOUT = 2.5V 2ms/DIV 3100 G23 0 5 2 2.5 VINBK (V) 3 3.5 4 4.5 5 VINBK (V) 3100 G21 3100 G22 Load Step Response, Fixed Frequency Mode 10mA to 100mA Output Voltage Ripple in Fixed Frequency and Burst Mode Operation Load Step Response, Burst Mode Operation Enabled 10mA to 100mA COUT = 10μF COUT = 10μF COUT = 10μF 100mA/DIV 50mV/DIV 50mA/DIV 50mV/DIV 50mV/DIV 50mV/DIV 5μs/DIV 3100 G24 200μs/DIV 3100 G25 200μs/DIV 3100 G26 3100fa 8 LTC3100 TYPICAL PERFORMANCE CHARACTERISTICS RUN Pin Threshold Voltage TA = 25°C, unless otherwise specified. Start-Up Delay Times vs VIN 450 0.625 400 0.575 FALLING 0.550 BUCK 350 RISING DELAY TIME (μs) THRESHOLD (V) 0.600 BOOST 300 250 200 LDO 150 100 0.525 50 0.500 1 1.5 2 2.5 3 3.5 4 4.5 5 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 VIN (V) VIN (V) 3100 G28 3100 G27 PIN FUNCTIONS SWBST (Pin 1): Switch Pin for the Boost Converter. Connect the boost inductor between SWBST and VINBST. Keep PCB trace lengths as short and wide as possible to reduce EMI. If the inductor current falls to zero, an internal anti-ringing switch is connected from SWBST to VINBST to minimize EMI. VBST (Pin 2): Output Voltage for the Boost Converter (which is the drain of the internal synchronous rectifier) and Input Voltage for the LDO. PCB trace length from VBST to the output filter capacitor (10μF minimum) should be as short and wide as possible. VLDO (Pin 3): Output Voltage of the LDO Regulator. Connect a 1μF ceramic capacitor between VLDO and GND. Larger values of capacitance may be used for higher PSRR or improved transient response. SWBK (Pin 4): Switch Pin for the Buck Converter. Connect the buck inductor between SWBK and the buck output filter capacitor. Keep PCB trace lengths as short and wide as possible to reduce EMI. VINBK (Pin 5): Input Voltage for the Buck Converter. Connect a minimum of 4.7μF ceramic decoupling capacitor from this pin to ground. PGBK (Pin 6): Open-Drain Output That Pulls Low When FBBK Is More Than 8% Below Its Regulated Voltage. Con- nect a pull-up resistor from this pin to a positive supply less than 6V. GND (Pin 7): Signal Ground. Provide a short, direct PCB path between GND and the PC board ground plane connected to the Exposed Pad. RUNBK (Pin 8): Logic-Controlled Shutdown Input for the Buck Converter. There is an internal 4MΩ pull-down on this pin. RUNBK = High: Normal operation RUNBK = Low: Shutdown FBBK (Pin 9): Feedback Input to the gm Error Amplifier for the Buck Converter. Connect the resistor divider tap to this pin. The output voltage can be adjusted from 0.6V to 5.5V by: ⎛ R6 ⎞ VOUT _ BUCK = 0 . 600 V • ⎜ 1 + ⎟ ⎝ R5 ⎠ RUNLDO (Pin 10): Logic-Controlled Shutdown Input for the LDO Regulator. There is an internal 4MΩ pull-down on this pin. RUNLDO = High: Normal operation RUNLDO = Low: Shutdown 3100fa 9 LTC3100 PIN FUNCTIONS FBLDO (Pin 11): Feedback Input to the gm Error Amplifier for the LDO Regulator. Connect the resistor divider tap to this pin. The output voltage can be adjusted from 0.6V to 5.25V by: ⎛ R4 ⎞ VOUT _ LDO = 0 . 600 V • ⎜ 1 + ⎟ ⎝ R3 ⎠ FBBST (Pin 12): Feedback Input to the gm Error Amplifier for the Boost Converter. Connect the resistor divider tap to this pin. The output voltage can be adjusted from 1.5V to 5.25V by: ⎛ R2 ⎞ VOUT _ BOOST = 1 . 20 V • ⎜ 1 + ⎟ ⎝ R1⎠ MODE (Pin 13): Logic-Controlled Mode Select Pin for Both the Boost and Buck Converters. There is an internal 1MΩ pull-up on this pin to the higher of VINBST, VBST or VINBK. RUNBST (Pin 14): Logic-Controlled Shutdown Input for the Boost Converter. There is an internal 4MΩ pull-down on this pin. RUNBST = High: Normal operation RUNBST = Low: Shutdown PGBST (Pin 15): Open-Drain Output That Pulls to Ground When FBBST Is More Than 8% Below Its Regulated Voltage. Connect a pull-up resistor from this pin to a positive supply less than 6V. VINBST (Pin 16): Input Voltage for the Boost Converter. Connect a minimum of 1μF ceramic decoupling capacitor from this pin to ground. Exposed Pad (Pin 17): The Exposed Pad must be soldered to the PCB ground plane. It serves as the power ground connection, and as a means of conducting heat away from the die. MODE = Float or High: Enables Burst Mode operation for both the boost and the buck. MODE = Low: Disables Burst Mode operation. Both converters will operate in fixed frequency mode regardless of load current. 3100fa 10 LTC3100 BLOCK DIAGRAM L1, 3.3μH VBATT1, 0.65V TO 5V VBOOST, 1.5V TO 5.25V CIN 2.2μF R2 16 1 VINBST 2 SWBST VBST 12 VSEL VINBK R1 WELL SWITCH VBEST PGBST VB VBEST VBEST OF 3 15 GATE DRIVERS AND ANTI-CROSS CONDUCTION 1.1V – + VREF VREF_GD VREF VREF_GD 3 + – IPK START_OSC IZERO MODE CONTROL THERMAL SHUTDOWN WELL SWITCH TSD BURST R4 ERROR AMPLIFIER 100mA – + ILIM – + VBST 1M 5 ILIM REF ISENSE FROM VBST, VBATT1 OR VBATT2 CIN 4.7μF UVLO LEVEL SHIFT SHUTDOWN CLK TSD SHUTDOWN LOGIC 4M GND VBUCK 0.6V TO 5V R6 COUT 4.7μF R5 3 + – PWM 0.55V 4 IZERO COMPARATOR SLOPE COMPARATOR PGBK 6 L1 3.3μH SWBK ISENSE ERROR AMPLIFIER + – SHUTDOWN LOGIC GATE DRIVERS AND ANTI-CROSS CONDUCTION + – RUNLDO RUNBK OFF ON + – IPK COMPARATOR WAKE 8 OFF ON 4M VINBK 4M MODE R3 10 SHUTDOWN 13 0.6V GATE CONTROL TSD ISET CLAMP SOFT-START COUT 1μF FBLDO 11 RUNLDO 1.2V RUNBST 14 VLDO 0.6V TO 5V VLDO 3 ERROR AMPLIFIER/ SLEEP COMPARATOR FB LOGIC – + 0.15Ω + – CLK 1.5MHz OSC IZERO COMPARATOR SLOPE COMPARATOR IPK COMPARATOR START-UP OFF ON COUT 10μF FBBST VBST FBBK 9 0.6V PAD 7 PGND 3100 BD 3100fa 11 + – LTC3100 OPERATION The LTC3100 includes an 700mA synchronous step-up (boost) converter, a 250mA synchronous step-down (buck) converter and a 100mA low dropout (LDO) linear regulator housed in a 16-lead 3mm × 3mm QFN package. Both converters utilize current mode PWM control for exceptional line and load regulation and operate from the same 1.5MHz oscillator. The current mode architecture with adaptive slope compensation also provides excellent transient load response, requiring minimal output filtering. Both converters have internal soft-start and internal loop compensation, simplifying the design process and minimizing the number of external components. requirement for a large input capacitor. The limiting factor for the application becomes the ability of the power source to supply sufficient energy to the output at low input voltages, and maximum duty cycle of the converter, which is clamped at 90% (typical). Note that at low input voltages, even small input voltage drops due to series resistance become critical, and greatly limit the power delivery capability of the converter. With its low RDS(ON) and low gate charge internal MOSFET switches and synchronous rectifiers, the LTC3100 achieves high efficiency over a wide range of load current. Burst Mode operation maintains high efficiency at very light loads, but can be disabled for noise-sensitive applications. The internal soft-start circuitry ramps the peak boost inductor current from zero to its peak value of 700mA in approximately 800μs, allowing start-up into heavy loads. The soft-start circuitry is reset in the event of a commanded shutdown or an overtemperature shutdown. With separate power inputs for the boost and buck converters, along with independent enable and power good functions, the LTC3100 is very flexible. The two converters can operate from the same input supply, or from two different sources, or can even be cascaded by powering the buck converter from the output of the boost converter. By using the LDO as well, three different output voltages can be generated from a single alkaline/NiMH cell (or the LDO can be used for power sequencing the boost output). Operation can be best understood by referring to the Block Diagram. LOW NOISE FIXED FREQUENCY OPERATION Soft-Start Oscillator An internal oscillator sets the switching frequency to 1.5MHz. The oscillator allows a maximum duty cycle of 90% (typical) for the boost converter. Shutdown The boost converter is shut down by pulling the RUNBST pin below 0.3V, and activated by pulling the RUNBST pin above 0.9V. Note that RUNBST can be driven above VIN or VOUT, as long as it is limited to less than the absolute maximum rating. BOOST CONVERTER Error Amplifier Low Voltage Start-Up The error amplifier is a transconductance type. The non-inverting input is internally connected to the 1.20V reference and the inverting input is connected to FBBST. Clamps limit the minimum and maximum error amp output voltage for improved large signal transient response. Power converter control loop compensation is provided internally. A voltage divider from VBST to ground programs the output voltage (via FBBST) from 1.5V to 5.25V, according to the formula: ⎛ R2 ⎞ VBST = 1 . 20 V • ⎜ 1 + ⎟ ⎝ R1⎠ The LTC3100 boost converter includes an independent start-up oscillator designed to start up at an input voltage of 0.65V (typical). Soft-start and inrush current limiting are provided during start-up, as well as in normal mode. When either VINBST or VBST exceeds 1.4V (typical), the IC enters normal operating mode. Once the output voltage exceeds the input by 0.24V, the IC powers itself from VBST instead of VINBST. At this point, the internal circuitry has no dependency on the input voltage, eliminating the 3100fa 12 LTC3100 OPERATION Current Sensing Lossless current sensing converts the peak current signal of the N-channel MOSFET switch into a voltage which is summed with the internal slope compensation. The summed signal is compared to the error amplifier output to provide a peak current control command for the PWM. Current Limit The current limit comparator shuts off the N-channel MOSFET switch once its threshold is reached. Peak switch current is no less than 700mA, independent of input or output voltage, unless VOUT falls below 1V, in which case the current limit is cut in half to minimize power dissipation into a short-circuit. Slope Compensation Current mode control requires the use of slope compensation to prevent subharmonic oscillations in the inductor current waveform at high duty cycle operation. This is accomplished internally on the LTC3100 through the addition of a compensating ramp to the current sense signal. The LTC3100 performs current limiting prior to addition of the slope compensation ramp and therefore achieves a peak inductor current limit that is independent of duty cycle. Zero Current Comparator The zero current comparator monitors the boost inductor current to the output and shuts off the synchronous rectifier once this current reduces to approximately 30mA. This prevents the inductor current from reversing in polarity, improving efficiency at light loads. Synchronous Rectifier To control inrush current and to prevent the inductor current from running away when VOUT is close to VIN , the P-channel MOSFET synchronous rectifier is only fully enabled when VOUT > (VIN + 0.24V). Anti-Ringing Control The anti-ring circuitry connects a resistor across the boost inductor to prevent high frequency ringing on the SW pin during discontinuous current mode operation. The ringing of the resonant circuit formed by L and CSW (capacitance on SWBST pin) is low energy, but can cause EMI radiation. PGOOD Comparator The PGBST pin is an open-drain output which indicates the status of the boost converter output voltage. If the boost output voltage falls 8% below the regulation voltage, the PGBST open-drain output will pull low. The output voltage must rise 3% above the falling threshold before the pulldown will turn off. In addition, there is a 60μs (typical) deglitching delay in order to prevent false trips due to voltage transients on load steps. The PGBST output will also pull low if the boost converter is disabled. The typical PGBST pull-down switch resistance is 13Ω when VBST or VINBST equals 3.3V. Output Disconnect The LTC3100 boost converter is designed to allow true output disconnect by eliminating body diode conduction of the internal P-channel MOSFET rectifier. This allows for VOUT to go to 0V during shutdown, drawing no current from the input source. It also allows for inrush current limiting at turn-on, minimizing surge currents seen by the input supply. Note that to obtain the advantages of output disconnect, there must not be an external Schottky diode connected between SWBST and VBST. The output disconnect feature also allows VOUT to be pulled high without any reverse current into the battery. VIN > VOUT Operation The LTC3100 boost converter will maintain voltage regulation even when the input voltage is above the desired output voltage. Note that the output current capability is slightly reduced in this mode of operation. Refer to the Typical Performance Characteristics section. Burst Mode Operation (for Boost and Buck Converters) Burst Mode operation for both converters can be enabled or disabled using the MODE pin. If MODE is grounded, Burst Mode operation is disabled for both the boost and 3100fa 13 LTC3100 OPERATION buck converters. In this case, both converters will remain in fixed frequency operation, even at light load currents. If the load is very light, they will exhibit pulse-skip operation. If MODE is raised above 0.9V, or left open, Burst Mode operation will be enabled for both converters. In this case, either converter may enter Burst Mode operation at light load, and return to fixed frequency operation when the load current increases. Refer to the Typical Performance Characteristics section to see the output load Burst Mode threshold vs VIN and VOUT. The two converters can enter or leave Burst Mode operation independent of each other. In Burst Mode operation, each converter still switches at a frequency of 1.5MHz, using the same error amplifier and loop compensation for peak 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 it reaches the nominal regulation value, then the LTC3100 transitions to sleep mode where the outputs are off and the LTC3100 consumes only 15μA of quiescent current from VBST. Once the output voltage has drooped slightly, switching resumes again. This maximizes efficiency at very light loads by minimizing switching and quiescent losses. Burst Mode operation output ripple is typically 1% peak-to-peak. Burst Mode operation for the boost converter is inhibited during start-up, and until soft-start is complete and VBST is at least 0.24V greater than VINBST. Short-Circuit Protection The LTC3100 output disconnect feature allows output short-circuit while maintaining a maximum internally set current limit. To reduce power dissipation under shortcircuit conditions, the boost peak switch current limit is reduced to 400mA (typical). Schottky Diode Although it is not required, adding a Schottky diode from SWBST to VBST will improve efficiency by about 2%. Note that this defeats the boost output disconnect and shortcircuit protection features. BUCK CONVERTER OPERATION The buck converter provides a high efficiency, lower voltage output and supports 100% duty cycle operation to extend battery life. The buck converter uses the same 1.5MHz oscillator used by the boost converter. PWM Mode Operation When the MODE pin is held low, the LTC3100 buck converter uses a constant-frequency, current mode control architecture. Both the main (P-channel MOSFET) and synchronous rectifier (N-channel MOSFET) switches are internal. At the start of each oscillator cycle, the P-channel switch is turned on and remains on until the current waveform with superimposed slope compensation ramp exceeds the error amplifier output. At this point, the synchronous rectifier is turned on and remains on until the inductor current falls to zero or a new switching cycle is initiated. As a result, the buck converter operates with discontinuous inductor current at light loads which improves efficiency. At extremely light loads, the minimum on-time of the main switch will be reached and the buck converter will begin turning off for multiple cycles (pulse-skipping) in order to maintain regulation. Burst Mode Operation When the MODE pin is forced high, or left open, the buck converter will automatically transition between Burst Mode operation at sufficiently light loads (below approximately 10mA) and PWM mode at heavier loads. Burst Mode operation entry is determined by the peak inductor current and therefore the load current at which Burst Mode operation will be entered depends on the input voltage, the output voltage and the inductor value. Typical curves for Burst Mode operation entry threshold are provided in the Typical Performance Characteristics section of this data sheet. The quiescent current on VINBK in Burst Mode operation is only 15μA. If the boost converter is enabled and VINBST or VBST are at a higher potential than VINBK, some of the quiescent current will be supplied by the boost converter, reducing the burst quiescent current on VINBK to just 9μA. 3100fa 14 LTC3100 OPERATION Dropout Operation As the input voltage decreases to a value approaching the output regulation voltage, the duty cycle increases toward the maximum on-time. Further reduction of the supply voltage will force the main switch to remain on for more than one cycle until 100% duty cycle operation is reached where the main switch remains on continuously. In this dropout state, the output voltage will be determined by the input voltage less the resistive voltage drop across the main switch and series resistance of the inductor. Slope Compensation Current mode control requires the use of slope compensation to prevent subharmonic oscillations in the inductor current waveform at high duty cycle operation. This is accomplished internally on the LTC3100 through the addition of a compensating ramp to the current sense signal. In some current mode ICs, current limiting is performed by clamping the error amplifier voltage to a fixed maximum. This leads to a reduced output current capability at low step-down ratios. In contrast, the LTC3100 performs current limiting prior to addition of the slope compensation ramp and therefore achieves a peak inductor current limit that is independent of duty cycle. Short-Circuit Protection When the buck output is shorted to ground, the error amplifier will saturate high and the P-channel MOSFET switch will turn on at the start of each cycle and remain on until the current limit trips. During this minimum on-time, the inductor current will increase rapidly and will decrease very slowly during the remainder of the period due to the very small reverse voltage produced by a hard output short. To eliminate the possibility of inductor current runaway in this situation, the buck converter switching frequency is reduced to approximately 375kHz when the voltage on FBBK falls below 0.3V. Soft-Start respond to output load transients which occur during this time. In addition, the output voltage rise time has minimal dependency on the size of the output capacitor or load current. Error Amplifier and Compensation The LTC3100 buck converter utilizes an internal transconductance error amplifier. Compensation of the feedback loop is performed internally to reduce the size of the application circuit and simplify the design process. The compensation network has been designed to allow use of a wide range of output capacitors while simultaneously ensuring rapid response to load transients. Undervoltage Lockout If the VINBK supply voltage decreases below 1.6V (typical), the buck converter will be disabled. The soft-start for the buck converter will be reset during undervoltage lockout to provide a smooth restart once the input voltage rises above the undervoltage lockout threshold. PGOOD Comparator The PGBK pin is an open-drain output which indicates the status of the buck converter output voltage. If the buck output voltage falls 8% below the regulation voltage, the PGBK open-drain output will pull low. The output voltage must rise 3% above the falling threshold before the pulldown will turn off. In addition, there is a 60μs typical deglitching delay in order to prevent false trips due to voltage transients on load steps. The PGBK output will also pull low during overtemperature shutdown and undervoltage lockout to indicate these fault conditions, or if the buck converter is disabled. The typical PGBK pull-down switch resistance is 13Ω when VINBK = 3.3V. Schottky Diode Although it is not required, adding a Schottky diode from SWBK to the ground plane will improve efficiency by about 2%. The buck converter has an internal voltage mode soft-start circuit with a nominal duration of 1.3ms. The converter remains in regulation during soft-start and will therefore 3100fa 15 LTC3100 OPERATION LDO REGULATOR OPERATION COMMON FUNCTIONS The LDO regulator utilizes an internal 1.3Ω (typical) P-channel MOSFET pass device to supply up to 100mA of load current with a typical dropout voltage of 130mV. The input voltage to the LDO is internally connected to the boost output (VBST pin), and can share the same filter capacitor. The LDO can be operated independently of the boost (or buck) converter, providing a sufficient voltage is present on VBST. Oscillator Soft-Start and Current Limit The MODE pin is used to force fixed frequency operation (MODE < 0.3V) or to enable Burst Mode operation (MODE > 0.9V) for both the boost and buck converters. With Burst Mode operation enabled, the two converters will automatically enter or leave Burst Mode operation independently, based on their respective load conditions. There is an internal 1MΩ pull-up on MODE, in the event that the pin is left open. The LDO has an independent current limit circuit that limits output current to 120mA (typical). To minimize loading on the boost converter output when enabling the LDO, the LDO current limit is soft-started over a 500μs period. Therefore the rise time of the LDO output voltage will depend on the amount of capacitance on the VLDO pin. Reverse Current Blocking The LDO is designed to prevent any reverse current from VLDO back to the VBST pin, both in normal operation and in shutdown. If VLDO is pulled above VBST and VBST is above 1V, there will be a small (1μA typical) current from VLDO to ground. The 1.5MHz oscillator is shared by the boost and buck converters. It will be oscillating if either converter is enabled. If both converters are enabled, the boost N-channel MOSFET switch will be turned on coincident with the buck P-channel MOSFET switch. MODE Control Note: Leaving the pin open, or connecting it to the highest of VINBK or VBST, will result in the lowest Burst Mode quiescent current. Overtemperature Shutdown If the die temperature exceeds 150°C (typical) both converters and the LDO regulator will be disabled. All power devices will be turned off and all switch nodes will be high impedance. The soft-start circuits for both converters and the LDO are reset during overtemperature shutdown to provide a smooth recovery once the overtemperature condition is eliminated. Both converters and the LDO will restart (if enabled) when the die temperature drops to approximately 130°C. 3100fa 16 LTC3100 APPLICATIONS INFORMATION PC Board Layout Guidelines should be placed as close to the IC as possible and should have the shortest possible paths to ground. The LTC3100 switches large currents at high frequencies. Special care should be given to the PC board layout to ensure stable, noise-free operation. You will not get advertised performance with a careless layout. Figure 1 depicts the recommended PC board layout. A large ground pin copper area will help to lower the chip temperature. A multilayer board with a separate ground plane is ideal, but not absolutely necessary. 2. To prevent large circulating currents from disrupting the output voltage sensing, the ground for each resistor divider should be returned directly to the ground plane near the IC. 3. Use of vias in the die attach pad of the IC 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 PC board. A few key guidelines follow: 16 SWBST 1 15 14 MODE RUNBST PGBST 4. Keep the connection from the resistor dividers to the feedback pins as short as possible and away from the switch pin connections. VINBST 1. All circulating high current paths should be kept as short as possible. Capacitor ground connections should via down to the ground plane in the shortest route possible. The bypass capacitors on all VIN and VOUT pins 13 12 FBBST LTC3100 VBST 2 11 FBLDO VLDO 3 10 SWBK 4 RUNLDO 9 FBBK 8 RUNBK 7 GND 6 PGBK VINBK 5 VBUCK 3100 F01 Figure 1. Recommended Component Placement for Two-Layer PC Board 3100fa 17 LTC3100 APPLICATIONS INFORMATION COMPONENT SELECTION Boost Output Voltage Programming The boost output voltage is set by a resistive divider according to the following formula: ⎛ R2 ⎞ VOUT = 1 . 200 V • ⎜ 1 + ⎟ ⎝ R1⎠ Boost Inductor Selection The LTC3100 boost converter can utilize small surface mount and chip inductors due to the fast 1.5MHz 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 minimum boost inductance value is given by: ( VIN(MIN) • VOUT(MAX ) − VIN(MIN) Table 1. Recommended Boost Inductors VENDOR The external divider is connected to the output as shown in the Block Diagram. A feedforward capacitor may be placed in parallel with resistor R2 to improve the noise immunity of the feedback node, improve transient response and reduce output ripple in Burst Mode operation. A value of 33pF will generally suffice. L> do not have enough core area to support the peak inductor currents of 800mA seen on the LTC3100. To minimize radiated noise, use a shielded inductor. See Table 1 for suggested components and suppliers. ) 1 . 5 • RIPPLE • VOUT(MAX ) Where: RIPPLE = Allowable Inductor Current Ripple (Amps Peakto-Peak) VIN(MIN) = Minimum Input Voltage VOUT(MAX) = Maximum Output Voltage 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 DCR (series resistance of the winding) to reduce the I2R power losses, and must not saturate at peak inductor current levels. Molded chokes and some chip inductors usually Coilcraft (847) 639-6400 www.coilcraft.com PART/STYLE LPS4012, LPS4018 MSS4020, MSS5131 Coiltronics SD14, SD3814, SD3118 FDK MIPSA2520 MIPW3226 Murata www.murata.com LQH43C Sumida (847) 956-0666 www.sumida.com CDRH2D18, CDRH2D16 CDRH3D14, CDRH3D16 CDRH4D14, CDRH4D16 Taiyo-Yuden www.t-yuden.com NR3015 NP03SB TDK www.tdk.com VLP VLF, VLCF Toko (408) 432-8282 www.tokoam.com D518LC D52LC DP418C Würth (201) 785-8800 www.we-online.com WE-TPC Type S, M Boost Input and Output Capacitor Selection The internal loop compensation of the LTC3100 boost converter is designed to be stable with output capacitor values of 4.7μF or greater. Low ESR (equivalent series resistance) capacitors should be used to minimize the output voltage ripple. Multilayer ceramic capacitors are an excellent choice as they have extremely low ESR and are available in small footprints. A 4.7μF to 10μF output capacitor is sufficient for most fixed frequency applications. For applications where Burst Mode operation is enabled, a minimum value of 20μF is recommended. Larger values may be used to obtain very low output ripple and to improve transient response. X5R and X7R dielectric materials are preferred for their ability to maintain capacitance over wide voltage and temperature ranges. Y5V types should not be used. Case sizes smaller than 0805 are not recommended due to their increased DC bias effect. 3100fa 18 LTC3100 APPLICATIONS INFORMATION Low ESR input capacitors reduce input switching noise and reduce the peak current drawn from the battery. It follows that ceramic capacitors are also a good choice for input decoupling and should be located as close as possible to the device. A 2.2μF input capacitor on the VINBST pin is sufficient for most applications. Larger values may be used without limitations. For applications where the power source is more than a few inches away, a larger bulk decoupling capacitor is recommended on the input to the boost converter. Table 2 shows a list of several ceramic capacitor manufacturers. Consult the manufacturers directly for detailed information on their selection of capacitors. Note that even X5R and X7R type ceramic capacitors have a DC bias effect which reduces their capacitance with a DC voltage applied. This effect is particularly bad for capacitors in the smallest case sizes. Consult the manufacturer’s data for the capacitor you select to be assured of having the necessary capacitance in your application. Table 2.Capacitor Vendor Information SUPPLIER PHONE WEB SITE AVX (803) 448-9411 www.avxcorp.com Murata (714) 852-2001 www.murata.com Taiyo-Yuden (408) 573-4150 www.t-yuden.com TDK (847) 803-6100 www.component.tdk.com Buck Inductor Selection The choice of buck inductor value influences both the efficiency and the magnitude of the output voltage ripple. Larger inductance values will reduce inductor current ripple and will therefore lead to lower output voltage ripple. For a fixed DC resistance, a larger value inductor will yield higher efficiency by lowering the peak current to be closer to the average. However, a larger value inductor within the same family will generally have a greater series resistance, thereby offsetting this efficiency advantage. Given a desired peak to peak current ripple, ΔIL , the required inductance can be calculated via the following expression, where f represents the switching frequency in MHz: L= 1 fΔ IL ⎛ ⎞ V • ⎜ 1 − OUT ⎟ ( μ H) VIN ⎠ ⎝ A reasonable choice for ripple current is ΔIL = 100mA which represents 40% of the maximum 250mA load current. The DC current rating of the inductor should be at least 450mA to avoid saturation under overload or short-circuit conditions. To optimize efficiency the inductor should have a low series resistance. In particularly space restricted applications it may be advantageous to use a much smaller value inductor at the expense of larger ripple current. In such cases, the converter will operate in discontinuous conduction for a wider range of output loads and efficiency will be reduced. In addition, there is a minimum inductor value required to maintain stability of the current loop (given the fixed internal slope compensation). Specifically, if the buck converter is going to be utilized at duty cycles over 40%, the inductance value must be at least LMIN as given by the following equation: LMIN = 2.5 • VOUT (μH) Table 3 depicts the minimum required inductance for several common output voltages. Table 3.Buck Minimum Inductance OUTPUT VOLTAGE MINIMUM INDUCTANCE 0.6V 1.5μH 0.8V 2μH 1.2V 3μH 2V 5μH 2.7V 6.8μH 3.3V 8.3μH Larger values of inductor will also provide slightly greater output current capability before reaching current limit (by reducing the peak-to-peak ripple current). 3100fa 19 LTC3100 APPLICATIONS INFORMATION Table 4. Recommended Buck Inductors VENDOR Coilcraft (847) 639-6400 www.coilcraft.com PART/STYLE LPS3008, LPS3010, LPS3015 Coiltronics SD3114, SD3118, SD3112 FDK MIPF2016 MIPF2520, MIPS2520 Murata www.murata.com LQH32C LQM31P Sumida (847) 956-0666 www.sumida.com CDRH2D11, CDRH2D09 CMD4D06-4R7MC CMD4D06-3R3MC Taiyo-Yuden www.t-yuden.com NR3010, NR3012 TDK www.tdk.com the value of the feedforward capacitor in parallel with the upper resistor divider resistor. Note that even X5R and X7R type ceramic capacitors have a DC bias effect which reduces their capacitance with a DC voltage applied. This effect is particularly bad for capacitors in the smallest case sizes. Consult the manufacturer’s data for the capacitor you select to be assured of having the necessary capacitance in your application. Table 5. Buck Output Capacitor Range VOUT CMIN CMAX 0.6V 15μF 300μF 0.8V 15μF 230μF VLF3010, VLF3012 LEMC3225, LBC2518 1.2V 10μF 150μF 1.8V 6.8μF 90μF Toko (408) 432-8282 www.tokoam.com D3010 DB3015 D312, D301F 2.7V 6.8μF 70μF 3.3V 6.8μF 50μF Würth (201) 785-8800 www.we-online.com WE-TPC Type XS, S Buck Output Capacitor Selection A low ESR output capacitor should be utilized at the buck output in order to minimize voltage ripple. Multilayer ceramic capacitors are an excellent choice as they have low ESR and are available in small footprints. In addition to controlling the output ripple magnitude, the value of the output capacitor also sets the loop crossover frequency and therefore can impact loop stability. There is both a minimum and maximum capacitance value required to ensure stability of the loop. If the output capacitance is too small, the loop crossover frequency will increase to the point where switching delay and the high frequency parasitic poles of the error amplifier will degrade the phase margin. In addition, the wider bandwidth produced by a small output capacitor will make the loop more susceptible to switching noise. At the other extreme, if the output capacitor is too large, the crossover frequency can decrease too far below the compensation zero and also lead to degraded phase margin. Table 5 provides a guideline for the range of allowable values of low ESR output capacitors. Larger value output capacitors can be accommodated provided they have sufficient ESR to stabilize the loop or by increasing Buck Input Capacitor Selection The VINBK pin provides current to the buck converter power switch and is also the supply pin for the buck’s internal control circuitry. It is recommended that a low ESR ceramic capacitor with a value of at least 4.7μF be used to bypass this pin. The capacitor should be placed as close to the pin as possible and have a short return to ground. For applications where the power source is more than a few inches away, a larger bulk decoupling capacitor is recommended. Buck Output Voltage Programming The output voltage is set by a resistive divider according to the following formula: ⎛ R6 ⎞ VOUT = 0 . 600 V • ⎜ 1 + ⎟ ⎝ R5 ⎠ The external divider is connected to the output as shown in the Block Diagram. It is recommended that a feedforward capacitor be placed in parallel with resistor R6 to improve the noise immunity of the feedback node and reduce output ripple in Burst Mode operation. A value of 10pF will generally suffice. 3100fa 20 LTC3100 APPLICATIONS INFORMATION LDO Output Capacitor Selection LDO Output Voltage Programming The LDO is designed to be stable with a minimum 1μF output capacitor. No series resistor is required when using low ESR capacitors. For most applications, a 2.2μF ceramic capacitor is recommended. Larger values will improve transient response, and raise the power supply rejection ratio (PSRR) of the LDO. Refer to the Typical Performance Characteristics for the allowable range of output capacitor to ensure loop stability. The output voltage is set by a resistive divider according to the following formula: ⎛ R4 ⎞ VOUT = 0 . 600 V • ⎜ 1 + ⎟ ⎝ R3 ⎠ The external divider is connected to the output as shown in the Block Diagram. For improved transient response, a feedforward capacitor may be placed in parallel with resistor R4. TYPICAL APPLICATIONS Single-Cell Boost and Buck with Voltage Sequencing L1 3.3μH VBATT 0.9V TO 1.5V + 16 3.5V 1 5 SWBST VINBK 2 VBST FBBST VINBST CIN 2.2μF 12 13 14 10 8 SWBK 9 RUNLDO RUNBK GND R4 115k 11 4 FBBK 15 PGBST 16 PGBK VBST, 1V/DIV VI/O, 1V/DIV +3.3V AT 50mA V_I/O 3 MODE RUNBST C1 10μF s2 R1 523k FBLDO OFF ON R2 1M LTC3100 VLDO FF EN_BURST Output Voltages During Soft-Start for Sequenced Converter L2 3.3μH R3 25.5k C2 2.2μF VCORE, 1V/DIV 120mA AT VBATT = 0.9V 220mA AT VBATT = 1.2V V_CORE = 1.2V R6 1M R5 1M 1ms/DIV 3100 TA02b C3 10μF R7 1M R8 1M 7 BOOST_GOOD BUCK_GOOD 3100fa 21 LTC3100 TYPICAL APPLICATIONS Li-Ion Input, Triple Output Converter Efficiency vs Load Current 100 L1 3.3μH 16 R2 2M 12 FBBST VINBST CIN 4.7μF 2 VBST R1 634k R4 115k 11 FBLDO BOOST LDO BUCK OFF ON OFF ON OFF ON 14 10 8 MODE 9 FBBK RUNLDO RUNBK 4 SWBK RUNBST GND C2 2.2μF L2 4.7μH CFF2 10pF R6 976k 80 100 70 60 10 50 40 1 30 +1.8V AT 250mA V_CORE 1.8V BUCK 0.1 5V BOOST BUCK POWER LOSS BOOST POWER LOSS 0.01 0.1 1 10 100 1000 LOAD CURRENT (mA) 10 0 0.01 C3 10μF R7 100k R5 487k 1000 VIN = 3.6V 20 R3 25.5k 15 PGBST 16 PGBK 7 +3.3V AT 50mA V_I/O 3 VLDO LTC3100 13 C1 10μF s2 EFFICIENCY (%) 1 5 SWBST VINBK 90 3100 TA03a POWER LOSS (mW) VIN 2.5V TO 5V Li-Ion +5V AT 200mA VBOOST R8 100k 3100 TA03b BOOST_GOOD BUCK_GOOD Single-Cell/Two-Cell or USB Input to 3.3V/1.8V Converter MBR0520 VBATT 0.9V TO 3.3V 3.3V AT: 100mA FOR VBATT = 1.2V 300mA FOR VBATT = 2.4V 250mA FOR USB INPUT L1 3.3μH C1 4.7μF 16 C4 4.7μF 1 5 SWBST VINBK VINBST 2 VBST FBBST R1 1.07M 12 LTC3100 FBLDO 11 R3 301k R5 200k 1.8V AT 50mA R6 100k 13 14 R7 64.9k 10 8 R4 20k MODE SWBK RUNBST FBBK RUNLDO PGBST RUNBK GND PGBK 4 C4 2.2μF L2 10μH C3 10μF 9 VLDO 3.3V OUTPUT 90 VOUT C2 10μF R2 324k VLDO 3 100 80 VIN = 2.4V EFFICIENCY (%) USB INPUT Efficiency vs Load Current 70 VIN = 1.2V 60 50 40 VIN = 5V USB 30 20 10 0 0.01 0.1 1 10 100 LOAD CURRENT (mA) 1000 3100 TA04b 15 16 7 3100 TA04a 3100fa 22 LTC3100 PACKAGE DESCRIPTION UD Package 16-Lead Plastic QFN (3mm × 3mm) (Reference LTC DWG # 05-08-1691) 0.70 p0.05 3.50 p 0.05 1.45 p 0.05 2.10 p 0.05 (4 SIDES) PACKAGE OUTLINE 0.25 p0.05 0.50 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 3.00 p 0.10 (4 SIDES) BOTTOM VIEW—EXPOSED PAD PIN 1 NOTCH R = 0.20 TYP OR 0.25 s 45o CHAMFER R = 0.115 TYP 0.75 p 0.05 15 16 PIN 1 TOP MARK (NOTE 6) 0.40 p 0.10 1 1.45 p 0.10 (4-SIDES) 2 (UD16) QFN 0904 0.200 REF 0.00 – 0.05 NOTE: 1. DRAWING CONFORMS TO JEDEC PACKAGE OUTLINE MO-220 VARIATION (WEED-2) 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 0.25 p 0.05 0.50 BSC 3100fa 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. 23 LTC3100 TYPICAL APPLICATION Single-Cell to 1.2V/1.8V Converter L1 3.3μH + 16 CIN 2.2μF 1 5 SWBST VINBK 2 VBST VINBST FBBST VLDO R1 1M 12 FBLDO OFF ON 14 10 8 MODE SWBK RUNBST GND 7 R3 100k R6 1M 9 RUNLDO RUNBK 4 C2 2.2μF R4 200k L2 3.3μH FBBK 15 PGBST 6 PGBK R5 1M 80 1.8V AT 50mA VLDO 3 11 90 C1 10μF s2 R2 1M LTC3100 13 100 2.4V EFFICIENCY (%) VBATT 0.9V TO 1.6V Efficiency vs Load Current (VBUCK) 70 60 50 40 30 20 1.2V AT: 120mA FOR VBATT = 0.9V 250mA FOR VBATT = 1.2V VBUCK C3 10μF R7 100k 10 0 0.01 VIN = 0.9V VIN = 1.2V VIN = 1.5V 0.1 1 10 100 LOAD CURRENT ON VBUCK (mA) 1000 3100 TA05b 3100 TA05a BUCK_GOOD RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC3442 1.2A (IOUT), 2MHz Synchronous Buck-Boost DC/DC Converter VIN: 2.4V to 5.5V, VOUT(RANGE): 2.4V to 5.25V, IQ = 35μA, ISD < 1μA, DFN Package LTC3455 Dual DC/DC Converter with USB Power Manager and Li-Ion 96% Efficiency, Seamless Transition Between Inputs, IQ = 110μA, Battery Charger ISD < 2μA, QFN Package LTC3456 2-Cell Multi-Output DC/DC Converter with USB Power Manager 92% Efficiency, Seamless Transition Between Inputs, IQ = 180μA, ISD < 1μA, QFN Package LTC3520 Synchronous 1A Buck-Boost and 600mA Step-Down DC/DC Converter VIN: 2.2V to 5.5V, VOUT(MIN) = 0.6V, IQ = 55μA, ISD < 1μA, 4mm × 4mm QFN Package LTC3522 Synchronous 400mA Buck-Boost and 200mA Step-Down DC/DC Converter VIN: 2.4V to 5.5V, VOUT(MIN) = 0.6V, IQ = 25μA, ISD < 1μA, 3mm × 3mm QFN-16 Package LTC3527/LTC3527-1 Dual (400mA/800mA) Synchronous Boost Converter VIN: 0.5V to 5V, VOUT: 1.5V to 5.25V, IQ = 12μA, ISD < 2μA, 3mm × 3mm QFN Package LTC3530 600mA (IOUT), 2MHz Synchronous Buck-Boost DC/DC Converter VIN: 1.8V to 5.5V, VOUT(RANGE): 1.8V to 5.5V, IQ = 40μA, ISD < 1μA, DFN and MSOP Packages LTC3532 500mA (IOUT), 2MHz Synchronous Buck-Boost DC/DC Converter VIN: 2.4V to 5.5V, VOUT(RANGE): 2.4V to 5.25V, IQ = 35μA, ISD < 1μA, DFN and MSOP Packages LTC3537 600mA (ISW), 2.2MHz Synchronous Boost Converter with 100mA LDO VIN: 0.68V to 5V, VOUT(MAX) = 5.5V, IQ = 30μA, ISD < 1μA, 3mm × 3mm QFN Package LTC3538 600mA (IOUT), 2MHz Synchronous Buck-Boost DC/DC Converter VIN: 2.4V to 5.5V, VOUT(RANGE): 1.5V to 5.5V, IQ = 35μA, ISD < 1μA, DFN Package LTC3544/LTC3544B 300mA, 200mA ×2, 100mA, 2.25MHz Quad Output Synchronous Step-Down DC/DC Converter VIN: 2.25V to 5.5V, VOUT(MIN) = 0.8V, IQ = 70μA, ISD < 1μA, QFN Package LTC3545 Triple Output, 3mA × 800mA, 2.25MHz Synchronous Step-Down DC/DC Converter VIN: 2.25V to 5.5V, VOUT(MIN) = 0.6V, IQ = 58μA, ISD < 1μA, QFN Package 3100fa 24 Linear Technology Corporation LT 1108 REV A • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2008