ML4818CP

www.fairchildsemi.com ML4818 Phase Modulation/Soft Switching Controller Features • Full bridge phase modulation zero voltage switching circuit with programmable ZV transition times • Constant frequency operation to 500kHz • Current mode operation • Cycle-by-cycle current limiting with integrating fault detection and restart delay • Precision buffered 5V reference (+1%) • Four 1.5A peak current totem-pole output drivers • Under-voltage lockout circuit with 6V hysteresis • Power DIP package General Description The ML4818 is a complete phase modulation control IC suitable for full bridge soft switching converters. Unlike conventional PWM circuits, the phase modulation technique allows for zero-voltage switching transitions and square wave drive across the transformer. The IC modulates the phases of the two sides of the bridge to control output power. The ML4818 can be operated in current mode. The delay times for the outputs are externally programmable to allow the zero-voltage switching transitions to take place. Pulse-by-pulse current limit, integrating fault detection, and soft start reset are provided. The under-voltage lockout circuit features a 6V hysteresis with a low starting current to allow off-line start up with a low power bleed resistor. A shutdown function powers down the IC, putting it into a low quiescent state. Block Diagram 10 SHUTDOWN REFERENCE AND UNDER-VOLTAGE LOCKOUT INHIBIT OUTPUTS R Q 3 5 RAMP E/A OUT 0.7V S VCC VREF 24 13 11 2 CLOCK RT CT OSC 20 + + Q DELAY A2 OUT 16 ΦMOD – T FLIP FLOP V+ I1 VCC A1 OUT 8 INV +5V ERROR AMP – T Q DELAY 17 + 9 SOFT START 3V VCC B1 OUT – + R DELAY 22 VCC R 12 RCRESET ILIM 1V Q I2 S S Q B2 OUT DELAY 21 RDELAY GND *PINS 1, 6, 7, 15, 18, 19 AND 23 ARE GND 4 + – 14 * REV. 1.0.3 6/21/01 ML4818 PRODUCT SPECIFICATION Pin Configuration 24-Pin Power DIP (P24) GND CT RAMP ILIM E/A OUT GND GND INV SOFT START SHUTDOWN RT RCRESET 1 2 3 4 5 6 7 8 9 10 11 12 24 23 22 21 20 19 18 17 16 15 14 13 VREF GND B1 OUT B2 OUT VCC GND GND A1 OUT A2 OUT GND RDELAY CLOCK TOP VIEW Pin Description Pin 1 2 3 4 5 6,7 8 9 10 11 12 13 14 15 16 17 18,19 20 21 22 23 24 Name GND CT RAMP ILIM E/A OUT GND INV SOFT START SHUTDOWN RT RCRESET CLOCK RDELAY GND A2 OUT A1 OUT GND VCC B2 OUT B1 OUT GND VREF Ground Timing capacitor for oscillator Non-inverting input to main comparator. Connected to current sense resistor for current mode Current limit sense pin. Normally connected to current sense resistor Output of error amplifier and input to PWM comparator Ground and substrate Inverting input to error amp Normally connected to soft start capacitor Pulling this pin low puts the IC into a power down mode and turns off all outputs. This pin is internally pulled up to VREF. Resistor which sets discharge current for oscillator timing capacitor Timing elements for Integrating fault detection and reset delay circuits Oscillator output Resistor to ground on this pin programs the amount of delay from the time an output turns off until its complementary output turns on Ground High current totem pole output A1 High current totem pole output A2 Ground and substrate Positive supply for the IC High current totem pole output B1 High current totem pole output B2 Ground Buffered output for the 5V voltage reference Function 2 REV. 1.0.3 6/21/01 PRODUCT SPECIFICATION ML4818 Absolute Maximum Ratings Absolute Maximum Ratings are those values, beyond which the device could be permanently damaged. Absolute maximum ratings are stress ratings only and functional device operation is not implied. Parameter VCC Output Driver Current, Source or Sink DC Pulse (0.5 µs) Analog Inputs (CT, RAMP, ILIM, E/A OUT, INV, SOFT START, RCRESET) CLOCK Output Current (RT) Error Amplifier Output Current (E/A OUT) SOFT START Sink Current Oscillator Charging Current (CT) Junction Temperature Storage Temperature Range Lead Temperature (Soldering 10 Sec) Thermal Resistance (θJA) Plastic Power DIP –65 –0.3 Min. Max. 30 0.5 1.5 6 –5 5 50 –5 150 150 260 40 Units V A A V mA mA mA mA °C °C °C °C/W Operating Conditions Parameter Operating Temperature Range Min. 0 Max. 70 Units °C Electrical Characteristics Unless otherwise specified, VCC = 15V, RT = 12.7kΩ, CT = 250pF, RCLK = 3kΩ, RDELAY = 5kΩ, TA = Operating Temperature Range (Note 1). Parameter Oscillator Initial Accuracy Voltage Stability Temperature Stability Total Variation CT Discharge Current Clock Out High Clock Out Low Ramp Peak Ramp Valley Ramp Valley to Peak Reference Output Voltage Line Regulation Load Regulation TA=25°C, IO=1mA 12V