LTC1871IMS-7#TRPBF

LTC1871-7 High Input Voltage, Current Mode Boost, Flyback and SEPIC Controller Description Features Optimized for High Input Voltage Applications n Wide Chip Supply Voltage Range: 6V to 36V n Internal 7V Low Dropout Voltage Regulator Optimized for 6V-Rated MOSFETs n Current Mode Control Provides Excellent Transient Response n High Maximum Duty Cycle (92% Typ) n ±2% RUN Pin Threshold with 100mV Hysteresis n ±1% Internal Voltage Reference n Micropower Shutdown: I = 10µA Q n Programmable Operating Frequency (50kHz to 1MHz) with One External Resistor n Synchronizable to an External Clock Up to 1.3 × f OSC n User-Controlled Pulse Skip or Burst Mode® Operation n Output Overvoltage Protection n Can be Used in a No R SENSE™ Mode for VDS < 36V n Small 10-Lead MSOP Package The LTC®1871-7 is a current mode, boost, flyback and SEPIC controller optimized for driving 6V-rated MOSFETs in high voltage applications. The LTC1871-7 works equally well in low or high power applications and requires few components to provide a complete power supply solution. The switching frequency can be set with an external resistor over a 50kHz to 1MHz range, and can be synchronized to an external clock using the MODE/SYNC pin. Burst Mode operation at light loads, a low minimum operating supply voltage of 6V and a low shutdown quiescent current of 10µA make the LTC1871-7 well suited for battery-operated systems. For applications requiring constant frequency operation, Burst Mode operation can be defeated using the MODE/SYNC pin. The LTC1871-7 is available in the 10-lead MSOP package. n PARAMETER n n n LTC1871 7.0V 5.2V UV + 5.6V 2.1V INTVCC UV– 4.6V 1.9V INTVCC Applications n LTC1871-7 INTVCC Telecom Power Supplies 42V Automotive Systems 24V Industrial Controls IP Phone Power Supplies L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks of Linear Technology Corporation. No RSENSE is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. Typical Application D3 10BQ060 VIN 36V TO 72V D2 4148 LTC1871-7 FB FREQ MODE/SYNC 110k 120k 47µF 16V X5R 10Ω VIN ITH 12.4k T1 VP1-0076 SENSE RUN 3.4k Q1 FMMT625 • D1 9.1V 2.2nF 3:1 100k • 2.2µF 100V X7R 604k 26.7k VOUT 12V 0.4A INTVCC M1 FDC2512 GATE GND 4.7µF X5R 0.1µF X5R 0.12Ω 18717 F01 Figure 1. Small, Nonisolated 12V Flyback Telecom Housekeeping Supply 18717fd 1 LTC1871-7 Absolute Maximum Ratings (Note 1) Pin Configuration VIN Voltage ................................................ – 0.3V to 36V INTVCC Voltage............................................ –0.3V to 9V INTVCC Output Current...........................................50mA GATE Voltage............................ –0.3V to VINTVCC + 0.3V ITH, FB Voltages........................................ –0.3V to 2.7V RUN Voltage................................................ –0.3V to 7V MODE/SYNC Voltage.................................... –0.3V to 9V FREQ Voltage............................................. –0.3V to 1.5V SENSE Pin Voltage..................................... –0.3V to 36V Operating Temperature Range (Note 2) LTC1871E-7...........................................–40°C to 85°C LTC1871I-7.......................................... –40°C to 125°C Junction Temperature (Note 3).............................. 125°C Storage Temperature Range................... –65°C to 150°C Lead Temperature (Soldering, 10 sec).................... 300°C TOP VIEW RUN ITH FB FREQ MODE/ SYNC 10 9 8 7 6 1 2 3 4 5 SENSE VIN INTVCC GATE GND MS PACKAGE 10-LEAD PLASTIC MSOP TJMAX = 125°C, θJA = 120°C/W Order Information LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LTC1871EMS-7#PBF LTC1871EMS-7#TRPBF LTG4 10-Lead Plastic MSOP –40°C to 85°C LTC1871IMS-7#PBF LTC1871IMS-7#TRPBF LTBTR 10-Lead Plastic MSOP –40°C to 125°C LEAD BASED FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LTC1871EMS-7 LTC1871EMS-7#TR LTG4 10-Lead Plastic MSOP –40°C to 85°C LTC1871IMS-7 LTC1871IMS-7#TR LTBTR 10-Lead Plastic MSOP –40°C to 125°C Consult LTC Marketing for parts specified with wider operating temperature ranges. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ electrical characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 8V, VRUN = 1.5V, RFREQ = 80k, VMODE/SYNC = 0V, unless otherwise specified. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Main Control Loop VIN(MIN) Minimum Input Voltage I-Grade (Note 2) IQ Input Voltage Supply Current Continuous Mode VMODE/SYNC = 5V, VFB = 1.4V, VITH = 0.75V ● VMODE/SYNC = 0V, VITH = 0.2V (Note 5) VMODE/SYNC = 0V, VITH = 0.2V (Note 5), I-Grade (Note 2) Shutdown Mode 6 V 6 V (Note 4) VMODE/SYNC = 5V, VFB = 1.4V, VITH = 0.75V, I-Grade (Note 2) Burst Mode Operation, No Load ● ● VRUN = 0V VRUN = 0V, I-Grade (Note 2) ● 550 1000 µA 600 1100 µA 280 500 µA 280 600 µA 12 25 µA 12 25 µA 18717fd 2 LTC1871-7 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 8V, VRUN = 1.5V, RFREQ = 80k, VMODE/SYNC = 0V, unless otherwise specified. SYMBOL PARAMETER VRUN+ Rising RUN Input Threshold Voltage VRUN – Falling RUN Input Threshold Voltage VRUN(HYST) RUN Pin Input Threshold Hysteresis IRUN RUN Input Current VFB Feedback Voltage CONDITIONS ● VITH = 0.2V (Note 5) VITH = 0.2V (Note 5), I-Grade (Note 2) IFB FB Pin Input Current VITH = 0.2V (Note 5) ∆VFB Line Regulation 6V ≤ VIN ≤ 30V ∆VIN Load Regulation ∆VITH TYP MAX 1.348 I-Grade (Note 2) ∆VFB MIN ● UNITS V 1.223 1.198 1.248 1.273 1.298 50 100 150 mV 35 100 175 mV 5 60 nA 1.230 1.242 1.248 V V 1.255 V ● 1.218 1.212 ● 1.205 V V 18 60 nA 0.002 0.02 %/V 0.002 0.02 %/V 6V ≤ VIN ≤ 30V, I-Grade (Note 2) ● VMODE/SYNC = 0V, VITH = 0.5V to 0.9V (Note 5) ● –1 –0.1 % VMODE/SYNC = 0V, VITH = 0.5V to 0.9V (Note 5) I-Grade (Note 2) ● –1 –0.1 % 2.5 6 ∆VFB(OV) ∆FB Pin, Overvoltage Lockout VFB(OV) – VFB(NOM) in Percent gm Error Amplifier Transconductance ITH Pin Load = ±5µA (Note 5) 600 VITH(BURST) Burst Mode Operation ITH Pin Voltage Falling ITH Voltage (Note 5) VSENSE(MAX) Maximum Current Sense Input Threshold Duty Cycle < 20% ISENSE(ON) SENSE Pin Current (GATE High) VSENSE = 0V 35 ISENSE(OFF) SENSE Pin Current (GATE Low) VSENSE = 30V Oscillator Frequency RFREQ = 80k Duty Cycle < 20%, I-Grade (Note 2) 10 µmho 0.3 120 ● 150 % V 180 mV 200 mV 70 µA 0.1 5 µA 250 300 350 kHz 300 350 kHz 100 Oscillator fOSC RFREQ = 80k, I-Grade (Note 2) ● 250 50 1000 kHz I-Grade (Note 2) ● 50 1000 kHz I-Grade (Note 2) ● Oscillator Frequency Range DMAX Maximum Duty Cycle 87 92 97 % 87 92 98.5 % 1.25 1.30 1.25 1.30 fSYNC/fOSC Recommended Maximum Synchronized Frequency Ratio fOSC = 300kHz (Note 6) tSYNC(MIN) MODE/SYNC Minimum Input Pulse Width VSYNC = 0V to 5V 25 ns tSYNC(MAX) MODE/SYNC Maximum Input Pulse Width VSYNC = 0V to 5V 0.8/fOSC ns VIL(MODE) Low Level MODE/SYNC Input Voltage VIH(MODE) fOSC = 300kHz (Note 6), I-Grade (Note 2) ● I-Grade (Note 2) ● I-Grade (Note 2) ● High Level MODE/SYNC Input Voltage RMODE/SYNC MODE/SYNC Input Pull-Down Resistance VFREQ Nominal FREQ Pin Voltage 0.3 V 0.3 V 1.2 V 1.2 V 50 kΩ 0.62 V Low Dropout Regulator VINTVCC INTVCC Regulator Output Voltage VIN = 8V VIN = 8V, I-Grade (Note 2) ● 6.5 7 7.5 V 6.5 7 7.5 V 18717fd 3 LTC1871-7 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 8V, VRUN = 1.5V, RFREQ = 80k, VMODE/SYNC = 0V, unless otherwise specified. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS UVLO INTVCC Undervoltage Lockout Threshold Rising INTVCC Falling INTVCC UVLO Hysteresis ∆VINTVCC INTVCC Regulator Line Regulation 8V ≤ VIN ≤ 15V 8 25 mV  ∆VIN1 ∆VINTVCC INTVCC Regulator Line Regulation 15V ≤ VIN ≤ 30V 70 200 mV VLDO(LOAD) INTVCC Load Regulation 0 ≤ IINTVCC ≤ 20mA, VIN = 8V VDROPOUT INTVCC Regulator Dropout Voltage tr tf 5.6 4.6 1.0 V V V  ∆VIN2 –2 –0.2 % VIN = 6V, INTVCC Load = 20mA 280 mV GATE Driver Output Rise Time CL = 3300pF (Note 7) 17 100 ns GATE Driver Output Fall Time CL = 3300pF (Note 7) 8 100 ns GATE Driver 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 LTC1871E-7 is guaranteed to meet performance specifications from 0°C to 70°C junction temperature. Specifications over the – 40°C to 85°C operating junction temperature range are assured by design, characterization and correlation with statistical process controls. The LTC1871I-7 is guaranteed over the full –40°C to 125°C operating junction temperature range. Note 3: TJ is calculated from the ambient temperature TA and power dissipation PD according to the following formula: TJ = TA + (PD • 120°C/W) Note 4: The dynamic input supply current is higher due to power MOSFET gate charging (QG • fOSC). See Applications Information. Note 5: The LTC1871-7 is tested in a feedback loop that servos VFB to the reference voltage with the ITH pin forced to a voltage between 0V and 1.4V (the no load to full load operating voltage range for the ITH pin is 0.3V to 1.23V). Note 6: In a synchronized application, the internal slope compensation gain is increased by 25%. Synchronizing to a significantly higher ratio will reduce the effective amount of slope compensation, which could result in subharmonic oscillation for duty cycles greater than 50%. Note 7: Rise and fall times are measured at 10% and 90% levels. typical performance characteristics FB Voltage vs Temp FB Voltage Line Regulation 1.25 FB Pin Current vs Temperature 60 1.231 50 1.23 FB PIN CURRENT (nA) FB VOLTAGE (V) FB VOLTAGE (V) 1.24 1.230 1.22 40 30 20 10 1.21 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C) 18717 G01 1.229 0 5 10 15 20 VIN (V) 25 30 35 18717 G02 0 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C) 18717 G03 18717fd 4 LTC1871-7 Typical Performance Characteristics Shutdown Mode IQ vs VIN Shutdown Mode IQ vs Temperature 30 20 600 VIN = 8V Burst Mode IQ vs VIN 20 10 BURST MODE IQ (µA) SHUTDOWN MODE IQ (µA) SHUTDOWN MODE IQ (µA) 500 15 10 5 400 300 200 100 0 0 10 20 VIN (V) 30 0 –50 –25 40 0 18717 G04 18 500 TIME (ns) IQ (mA) 40 10 8 6 FALL TIME 10 2 0 25 50 75 100 125 150 TEMPERATURE (°C) 0 200 400 600 800 FREQUENCY (kHz) RUN Thresholds vs VIN 10 20 VIN (V) 30 40 18717 G10 2000 4000 6000 8000 CL (pF) 10000 12000 18717 G09 RT vs Frequency 1.35 RT (kΩ) RUN THRESHOLDS (V) 1.3 0 1000 1.40 0 0 1200 RUN Thresholds vs Temperature 1.5 RUN THRESHOLDS (V) 1000 18717 G08 18717 G07 1.2 RISE TIME 30 20 4 100 1.4 40 50 12 0 30 60 14 0 –50 –25 20 VIN (V) Gate Drive Rise and Fall Time vs CL CL = 3300pF IQ(TOT) = 600µA + Qg • f 16 400 200 10 18717 G06 Dynamic IQ vs Frequency 300 0 18717 G05 Burst Mode IQ vs Temperature Burst Mode IQ (µA) 0 25 50 75 100 125 150 TEMPERATURE (°C) 1.30 100 1.25 1.20 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C) 18717 G11 10 0 100 200 300 400 500 600 700 800 900 1000 FREQUENCY (kHz) 18717 G12 18717fd 5 LTC1871-7 Typical Performance Characteristics Maximum Sense Threshold vs Temperature Frequency vs Temperature 325 SENSE Pin Current vs Temperature 35 160 GATE FREQUENCY (kHz) 315 310 305 300 295 290 285 155 SENSE PIN CURRENT (µA) MAX SENSE THRESHOLD (mV) 320 150 145 GATE HIGH VSENSE = 0V 30 280 275 –50 –25 0 140 –50 –25 25 50 75 100 125 150 TEMPERATURE (°C) 0 0 25 50 75 100 125 150 TEMPERATURE (°C) 18717 G14 18717 G13 INTVCC Load Regulation 18717 G15 INTVCC Dropout Voltage vs Current, Temperature INTVCC Line Regulation 500 7.2 VIN = 8V 450 6.9 DROPOUT VOLTAGE (mV) INTVCC VOLTAGE (V) 7.0 INTVCC VOLTAGE (V) 25 –50 –25 25 50 75 100 125 150 TEMPERATURE (°C) 7.1 7.0 150°C 400 125°C 350 75°C 300 25°C 250 200 0°C 150 –50°C 100 50 6.8 0 10 20 30 40 50 60 70 80 6.9 0 5 10 15 18717 G16 20 25 VIN (V) 30 35 40 18717 G17 0 0 5 10 15 INTVCC LOAD (mA) 20 18717 G18 pin functions RUN (Pin 1): The RUN pin provides the user with an accurate means for sensing the input voltage and programming the start-up threshold for the converter. The falling RUN pin threshold is nominally 1.248V and the comparator has 100mV of hysteresis for noise immunity. When the RUN pin is below this input threshold, the IC is shut down and the VIN supply current is kept to a low value (typ 10µA). The Absolute Maximum Rating for the voltage on this pin is 7V. ITH (Pin 2): Error Amplifier Compensation Pin. The current comparator input threshold increases with this control voltage. Nominal voltage range for this pin is 0V to 1.40V. FB (Pin 3): Receives the feedback voltage from the external resistor divider across the output. Nominal voltage for this pin in regulation is 1.230V. FREQ (Pin 4): A resistor from the FREQ pin to ground programs the operating frequency of the chip. The nominal voltage at the FREQ pin is 0.6V. 18717fd 6 LTC1871-7 Pin Functions MODE/SYNC (Pin 5): This input controls the operating mode of the converter and allows for synchronizing the operating frequency to an external clock. If the MODE/ SYNC pin is connected to ground, Burst Mode operation is enabled. If the MODE/SYNC pin is connected to INTVCC, or if an external logic-level synchronization signal is applied to this input, Burst Mode operation is disabled and the IC operates in a continuous mode. GND (Pin 6): Ground Pin. GATE (Pin 7): Gate Driver Output. INTVCC (Pin 8): The Internal 7V Regulator Output. The gate driver and control circuits are powered from this voltage. Decouple this pin locally to the IC ground with a minimum of 4.7µF low ESR tantalum or ceramic capacitor. This 7V regulator has an undervoltage lockout circuit with 5.6V and 4.6V rising and falling thresholds, respectively. VIN (Pin 9): Main Supply Pin. Must be closely decoupled to ground. SENSE (Pin 10): The Current Sense Input for the Control Loop. Connect this pin to a resistor in the source of the power MOSFET. Alternatively, the SENSE pin may be connected to the drain of the power MOSFET, in applications where the maximum VDS is less than 36V. Internal leading edge blanking is provided for both sensing methods. Block Diagram BIAS AND START-UP CONTROL SLOPE COMPENSATION RUN + 1 C2 – 1.248V VIN FREQ 4 0.6V V-TO-I PWM LATCH 85mV 1.230V + – S 50k OV R + 0.30V FB 3 1.230V 9 INTVCC IOSC MODE/SYNC 5 OSC – + EA + BURST COMPARATOR GATE 7 LOGIC Q GND CURRENT COMPARATOR + SENSE 10 C1 – – gm ITH V-TO-I 2 INTVCC 8 7V – 5.6V UP 4.6V DOWN + ILOOP LDO 1.230V SLOPE 1.230V UV TO START-UP CONTROL RLOOP GND BIAS VREF 6 18717 BD VIN 18717fd 7 LTC1871-7 operation Main Control Loop The LTC1871-7 is a constant frequency, current mode controller for DC/DC boost, SEPIC and flyback converter applications. With the LTC1871-7 the current control loop can be closed by sensing the voltage drop either across the power MOSFET switch or across a discrete sense resistor, as shown in Figure 2. L VIN D VOUT VIN + SENSE VSW COUT GATE GND GND 2a. SENSE Pin Connection for Maximum Efficiency (VSW < 36V) L VIN VIN D VOUT VSW GATE SENSE GND + COUT RS GND 18717 F02 2b. SENSE Pin Connection for Precise Control of Peak Current or for VSW > 36V Figure 2. Using the SENSE Pin On the LTC1871-7 For circuit operation, please refer to the Block Diagram of the IC and Figure 1. In normal operation, the power MOSFET is turned on when the oscillator sets the PWM latch and is turned off when the current comparator C1 resets the latch. The divided-down output voltage is compared to an internal 1.230V reference by the error amplifier EA, which outputs an error signal at the ITH pin. The voltage on the ITH pin sets the current comparator C1 input threshold. When the load current increases, a fall in the FB voltage relative to the reference voltage causes the ITH pin to rise, which causes the current comparator C1 to trip at a higher peak inductor current value. The average inductor current will therefore rise until it equals the load current, thereby maintaining output regulation. The nominal operating frequency of the LTC1871-7 is programmed using a resistor from the FREQ pin to ground and can be controlled over a 50kHz to 1000kHz range. In addition, the internal oscillator can be synchronized to an external clock applied to the MODE/SYNC pin and can be locked to a frequency between 100% and 130% of its nominal value. When the MODE/SYNC pin is left open, it is pulled low by an internal 50k resistor and Burst Mode operation is enabled. If this pin is taken above 2V or an external clock is applied, Burst Mode operation is disabled and the IC operates in continuous mode. With no load (or an extremely light load), the controller will skip pulses in order to maintain regulation and prevent excessive output ripple. The RUN pin controls whether the IC is enabled or is in a low current shutdown state. A micropower 1.248V reference and comparator C2 allow the user to program the supply voltage at which the IC turns on and off (comparator C2 has 100mV of hysteresis for noise immunity). With the RUN pin below 1.248V, the chip is off and the input supply current is typically only 10µA. An overvoltage comparator OV senses when the FB pin exceeds the reference voltage by 6.5% and provides a reset pulse to the main RS latch. Because this RS latch is reset-dominant, the power MOSFET is actively held off for the duration of an output overvoltage condition. The LTC1871-7 can be used either by sensing the voltage drop across the power MOSFET or by connecting the SENSE pin to a conventional shunt resistor in the source of the power MOSFET, as shown in Figure 2. Sensing the voltage across the power MOSFET maximizes converter efficiency and minimizes the component count, but limits the output voltage to the maximum rating for this pin (36V). By connecting the SENSE pin to a resistor in the source of the power MOSFET, the user is able to program output voltages significantly greater than 36V. Programming the Operating Mode For applications where maximizing the efficiency at very light loads (e.g.,