Document
November 1998 PRELIMINARY
ML4827* Fault-Protected PFC and PWM Controller Combo
GENERAL DESCRIPTION
The ML4827 is a controller for power factor corrected, switched mode power supplies, that includes circuitry necessary for conformance to the safety requirements of UL1950. A direct descendent of the industry-standard ML4824-1, the ML4827 adds a TriFault Detect™ function to guarantee that no unsafe conditions may result from single component failure in the PFC. Power Factor Correction (PFC) allows the use of smaller, lower cost bulk capacitors, reduces power line loading and stress on the switching FETs, and results in a power supply that fully complies with IEC1000-3-2 specification. The ML4827 includes circuits for the implementation of a leading edge, average current, “boost” type power factor correction and a trailing edge, pulse width modulator (PWM). The device is available in two versions; the ML4827-1 (Duty CycleMAX = 50%) and the ML4827-2 (Duty CycleMAX = 74%). The higher maximum duty cycle of the -2 allows enhanced utilization of a given transformer core’s power handling capacity. An overvoltage comparator shuts down the PFC section in the event of a sudden decrease in load. The PFC section also includes peak current limiting and input voltage brownout protection. The PWM section can be operated in current or voltage mode, and includes a duty cycle limit to prevent transformer saturation.
FEATURES
s s s s s
Pin-compatible with industry-standard ML4824-1 TriFault Detect™ to conform to UL1950™ requirements Available in 50% or 74% max duty cycle versions Low total harmonic distortion Reduces ripple current in the storage capacitor between the PFC and PWM sections Average current, continuous boost leading edge PFC High efficiency trailing-edge PWM can be configured for current mode or voltage mode operation Average line voltage compensation with brown-out control PFC overvoltage comparator eliminates output “runaway” due to load removal Current fed gain modulator for improved noise immunity Overvoltage protection, UVLO, and soft start
s s
s
s
s s
BLOCK DIAGRAM
16 VEAO VFB 15 2.5V IAC 2 VRMS 4 ISENSE 3 RAMP 1 7 RAMP 2 8 8V VDC 6 VCC SS 5 DC ILIMIT 9 8V 50µA 1.25V
– + – +
* Some Packages Are End Of Life
1 IEAO 3.5kΩ
+ –
POWER FACTOR CORRECTOR BROKEN WIRE COMPARATOR 2.7V OVP
+ –
2µA VREF VCCZ 13.5V
VCC
13 VREF
VEA –
+
IEA 0.5V
+
+ –
7.5V REFERENCE
14
S –1V
+ – –
Q Q PFC OUT Q Q 12
GAIN MODULATOR 3.5kΩ
R S R
PFC ILIMIT
OSCILLATOR DUTY CYCLE LIMIT
S VFB 2.5V
– +
Q Q
VIN OK 1V
– +
PWM OUT 11
R DC ILIMIT VCCZ UVLO
GND 10
PULSE WIDTH MODULATOR
1
ML4827
PIN CONFIGURATION
ML4827 16-Pin PDIP (P16) 16-Pin Wide SOIC (S16W)
IEAO IAC ISENSE VRMS SS VDC RAMP 1 RAMP 2 1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 VEAO VFB VREF VCC PFC OUT PWM OUT GND DC ILIMIT
TOP VIEW
PIN DESCRIPTION
PIN NAME FUNCTION PIN NAME FUNCTION
1 2 3 4 5 6 7 8
IEAO IAC I SENSE V RMS SS VDC RAMP 1 RAMP 2
PFC transconductance current error amplifier output PFC gain control reference input
9 10 11
DC ILIMIT GND
PWM current limit comparator input Ground
PWM OUT PWM driver output PFC OUT VCC V REF V FB PFC driver output Positive supply (connected to an internal shunt regulator) Buffered output for the internal 7.5V reference PFC transconductance voltage error amplifier input, and TriFault Detect input PFC transconductance voltage error amplifier output
Current sense input to the PFC current limit comparator Input for PFC RMS line voltage compensation Connection point for the PWM soft start capacitor PWM voltage feedback input PFC (master) oscillator input; fOSC set by RTCT When in current mode, this pin functions as as the current sense input; when in voltage mode, it is the PWM (slave) oscillator input.
12 13 14 15
16
VEAO
2
ML4827
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. VCC Shunt Regulator Current .................................. 55mA ISENSE Voltage ..................................................–3V to 5V Voltage on Any Other Pin ... GND – 0.3V to VCCZ + 0.3V I REF ............................................................................................ 20mA IAC Input Current .................................................... 10mA Peak PFC OUT Current, Source or Sink ................ 500mA Peak PWM OUT Current, Source or Sink .............. 500mA PFC OUT, PWM OUT Energy Per Cycle .................. 1.5µJ Junction Temperature .............................................. 150°C Storage Temperature Range ..................... –65°C to 150°C Lead Temperature (Soldering, 10 sec) ..................... 260°C Thermal Resistance (θJA) Plastic DIP ....................................................... 80°C/W Plastic SOIC .................................................. 105°C/W
OPERATING CONDITIONS
Temperature Range ML4827CX .....