PWM Controller

SEMICONDUCTOR AS2916 PWM Controller Description The AS2916 is a dual, full featured, pulse width modulation controller. The second controller is intended to run the auxiliary supply. Both controllers share common oscillator and power up logic. Based on an improved AS3842, the AS2916 provides additional features that reduce component count and improve specifications in a wide range of power supply designs. The added functionality also includes bulk voltage sensing, overvoltage input and soft-start. The PWM function is controlled by the current sense comparator for normal current mode control and a second comparator for voltage mode soft-start. A buffered RAMP signal is available for slope compensation without loading the oscillator. The output stage is a high current totem pole output that sees only 140 ns delay from the PWM comparators. The AS2916 requires less than 25 µA of startup current. The undervoltage lockout (UVLO) thresholds are nominally 13.5 V for turn-on and 7.5 V for turn-off. The oscillator discharge current is trimmed to provide guaranteed duty cycle clamping. The AS2916 has a second low frequency oscillator, which frequency modulates the operating frequency of the PWM by 25%, thus reducing EMI emissions. Features • • • • • • • • • • • • Dual PWM Controller Ultra low start-up current, less than 25µA Main converter soft-start Frequency randomizer for improved EMI performance Bulk detect circuitry Remote ON/OFF control Buffered ramp for slope compensation Optional auxiliary converter primary regulation High main converter drive capability Undervoltage lockout circuitry Accurate reference Standard temperature range extended to 105°C Top View Pin Configuration – 16L PDIP (16N) OUTB VCC REG SNSB CMPB SS RAMP OSC 1 2 3 4 5 6 7 8 16 15 14 13 12 11 16L SOIC (16D) PGND GND OUTA SNSA CMPA BOK OUTB VCC REG SNSB CMPB SS RAMP OSC 1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 PGND GND OUTA SNSA CMPA BOK ON WBL 10 ON 9 WBL Ordering Information AS2916 Circuit Type: PWM Controller Temperature Range: B = 0°C to 105°C B 16D N Packaging Option: T = Tubes N = Tape and Reel (13" Reel Dia) Package Style: 16D = 16 Pin, Plastic SOIC 16N = 16 Pin, Plastic DIP www.ptcc.com.tw 249 AS2916 Functional Block Diagram VREG 50µA 5V enable 5V Reg PWM Controller VCC REG BOK 2V5 + – (Bulk OK) S Q + R • UVLO – ON 2V5 SNSB VREG + – (RUN) AUX_ON 6µA SS CMPB 2R + – CM PWM 1V WBL OSC R (PWM) + – VCC OUTB SS PWM RT/CT OSC (Blank) GND RAMP x1 VCC (Blank) VCC gm (PWM) OUTA CMPA x1 2R 1V R AUX_ON – + GND CM PWM SNSA www.ptcc.com.tw 250 PWM Controller Pin Function Description Pin Number 1 Function OUTB Description AS2916 This is the gate drive output for the Main FET. The totem pole output has equivalent of an extra 10 Ω resistor to limit the FET turn on speed and a pull down resistor to ensure the FET gate is never open. No external circuitry except for the FET is expected on this pin. The largest FET expected to be driven is IRFBC40. If a larger power FET is used, a buffer might be required. Positive supply for the IC. Absolute maximum rating is 20 V. The running voltage shall be provided by the Auxiliary conver tor. Output of 5 V series regulator. This is the Main convertor current sense pin. An external RC filter from the Main power FET and slope compensation resistor from the RAMP pin is all the expected external circuitry. This is the Main output control pin. An opto isolated control signal from the secondary side error amplifier is buffered and connected to the invert pin of the main output current mode comparator. A pull-up current of 1 mA is provided so the only external circuitry expected is a common emitter opto-isolator. This pin provides a 6 µA current source to linearly charge an external capacitor. This spin is compared to the RAMP pin in the soft start comparator, terminating output pulses when RAMP goes above the SS voltage. While this pin is held low, the main output is inhibited. This pin is a level-shifted and buffered oscillator waveform, used to provide slope compensation for the Main and Auxiliary converters. The pin also serves as the non-inverting input of the soft-start comparator. Oscillator frequency and maximum duty cycle are set by connecting the resistor (RT) to VREG and a capacitor (CT) to ground. Provides an FM modulation of the oscillator, approximately ±25% deviation frequency, at a modulation rate set by an external cap at WBL. Shorting to GND eliminates modulation. This pin is used to remotely turn the main convertor ON/OFF either for normal user application or for protection. Bulk OK. This is a brownout protection feature. The pin monitors the bulk voltage through a resistor divider. When BOK exceeds 2.5 V a 50 µA current is sourced from the pin for hysteresis. When the pin drops below 2.5 V the hysteresis is turned off and SS is pulled low,inhibiting the main output. The Auxiliary output is not tied to BOK and will run as long as there is sufficient bias voltage. 2 VCC 3 4 REG SNSB 5 CMPB 6 SS 7 RAMP 8 OSC 9 WBL 10 11 ON BOK www.ptcc.com.tw 251 AS2916 Pin Function Description Pin Number 12 Function CMPA Description PWM Controller This is the Auxiliary convertor error amplifier compensation pin or if secondary controller is desired, the Auxiliary control input pin. A simple capacitor to ground is the only circuitry expected. Note: There is no external connection for voltage feedback. Voltage sensing is provided internally in such a way that VCC not loaded until it reaches predefined threshold. If secondary control is required, it can be forced into the CMPA pin. is 13 SNSA This is the Auxiliary convertor current sense pin. An external RC filter from the Auxiliary power FET and slope compensation resistor from the RAMP pin is all the expected external circuitry. This is the gate drive output for the Auxiliary FET. The totem pole output has equivalent of an extra 33 Ω resistor to limit the FET turn on speed and a pull down resistor to ensure the FET gate is never open. No external circuitry except for the FET is expected on this pin. The largest FET expected to be driven is IRF820. If a larger power FET is used, a buffer might be required. Signal ground. Power ground. 14 OUTA 15 16 GND PGND Absolute Maximum Ratings Parameter Reference Current Output Current Supply Voltage Output Voltage Continuous Power Junction Temperature Storage Temperature Lead Temperature (Soldering, 10 seconds) Symbol IREF IOUT VCC VOUT PD TJ TSTG TL Rating 200 1 20 20 500 150 –60 to +150 300 Unit mA A V V mW °C °C °C www.ptcc.com.tw 252 PWM Controller Electrical Characteristics AS2916 Electrical characteristics are guaranteed over the full junction temperature range (0-105°). Ambient temperature must be derated based upon power dissipation and package thermal characteristics. The conditions are: VCC = 15 V, BOK = 3 V, ON = 3 V, RT = 680 Ω, CT = 10 nF, and CWBL = 2.2 nF, unless otherwise specified. To override UVLO, VCC should be raised above UVLOHIGH prior to test. Parameter 5 V Regulator Output Voltage Line Regulation Load Regulation Temperature Stability Total Output Variation Long-Term Stability Output Noise Voltage Maximum Source Current Oscillator Initial Frequency Voltage Stability Temperature Stability Amplitude Upper Trip Point Lower Trip Point Discharge Current Duty Cycle Limit Over-Temperature Shutdown Wobble Oscillator Wobble Rate OSC Frequency Deviation Amplitude Upper Trip Point Lower Trip Point Charge Current Discharge Current FWBL DEV VWBL VH VL ICHRG IDSC 2.2 nF WBL to GND Change in main oscillator freq. VWBL peak-to-peak 3.4 +30 4.5 +40 1.8 2.7 0.9 VWBL = 0.7 V VWBL = 4.8 V –25 25 –36 36 –50 50 6.0 +50 kHz kHz V V V µA µA TOT TCF VOSC VH VL IDSC fOSC TA = 25°C, VWBL = 0 V 8.5 V ≤ VCC ≤ 18V TMIN ≤ TJ ≤ TMAX VOSC peak-to-peak VWBL = 0 V VWBL = 0 V VOSC = 3 V RT = 680 Ω, CT = 10 nF, TJ = 25°C 7.5 46 117 132 0.2 5 1.55 2.8 1.25 8.7 50 140 9.5 54 143 1.0 kHz % % V V V mA % °C VNOISE IMAX TCREG Line, Load, Temperature Over 1,000 hrs at 25°C 10 ≤ f ≤ 100 kHz, TJ = 25°C VREG = 4.8 V 4.85 5.0 50 30 120 180 VREG PSRR TJ = 25°C, IREG = 1 mA 12 ≤ VCC ≤ 18 V 1.0 ≤ IREG ≤ 20 mA 4.90 5.00 5 5 0.2 5.10 15 15 0.4 5.15 25 V mV mV mV/°C V mV µV mA Symbol Test Condition Min. Typ. Max. Unit www.ptcc.com.tw 253 AS2916 Electrical Characteristics PWM Controller Electrical characteristics are guaranteed over the full junction temperature range (0-105°). Ambient temperature must be derated based upon power dissipation and package thermal characteristics. The conditions are: VCC = 15 V, BOK = 3 V, ON = 3 V, RT = 680 Ω, CT = 10 nF, and CWBL = 2.2 nF, unless otherwise specified. To override UVLO, VCC should be raised above UVLOHIGH prior to test. Parameter Symbol Test Condition Min. Typ. Max. Unit Auxiliary PWM Comparator Input (CMPA) Regulation Voltage Transconductance Output Sink Current Output Source Current Output Swing High Output Swing Low VCCREG Gm ICMPALow VCC = 16 V, VCMPA = 1.1 V ICMPAHigh VCC = 12 V, VCMPA = 5 V VCMPAHigh VCC = 12 V, ICMPA = 0.5 mA VCMPALow VCC = 16 V, ICMPA = 2 mA AVSNSA VLS VSNSA IBIAS –0.2 ≤ VSNSA ≤ 0.8 V VSNSA = 0 V VCMPA = 5 V 0.95 13.4 14.5 1.0 2.0 –0.5 5.4 6.0 -1.1 5.7 0.2 1.1 15.7 V mS mA mA V V Auxiliary Current Sense Comparator (SNSA) Transfer Gain CMPA Level Shift Current Sense Threshold Input Bias Current 3.0 1.5 1.05 –1.0 80 1.15 –10 150 V/V V V µA ns Propagation Delay to Output tPD Main PWM Comparator Input (CMPB) Comp Source Current Comp Source Impedance Comp Source High ICMPB VCMPB = 2.5 V ZCMPB VCMPBHigh AVSNSB VLS –0.2 ≤ VSNSB ≤ 0.8 V VSNSB = 0 V VCMPB = 5 V 0.95 –1.0 10 5.4 –1.4 15 5.6 20 mA kΩ V Main Current Sense Comparator (SNSB) Transfer Gain CMPB Level Shift Current Sense Threshold Input Bias Current 3.0 1.5 1.05 –1.0 80 1.15 –10 150 V/V V V µA ns VSNSB IBIAS Propagation Dela