MC44603
Advance Information
Mixed Frequency Mode GreenLine PWM Controller:
Fixed Frequency, Variable Frequency, Standby Mode
GENERAL DISCRIPTION
The MC44603 is an enhanced high performance controller that is specifically designed for off-line and dc-to-dc converter
applicitions. This device has the unique ability of automatically changing operating modes if the converter
output is overloaded, unloaded, or shorted, offering the designer additional protection for increased system reliability.
The MC44603 has several distinguishing features when compared to conventional SMPS controllers.
These features consist of a foldback facility for overload protection, a standby mode when the converter output is
slightly loaded, a demagnetization detection for reduced switching stresses on transistor and diodes, and a high current
totem pole output ideally suited for driving a power MOSFET. It can also be used for driving bipolar transistor in low
power converters (<150 W). It is optimized to operate in continuous mode. It?s advanced design allows use in current
mode or voltage mode control applications.
FEATURES :
Current or Voltage Mode Controller
nOperation up to 250 kHz Output Switching Frequency
nInherent Feed Forward Compensation
nLatching PWM for Cycle-by-Cycle Current Limiting
nOscillator with Precise Frequency Control
High Flexibility
nExternally Programmable Reference Current
nSecondary or Primary Sensing
nSynchronization Facility
nHigh Current Totem Pole Output
nUndervoltage Lockout with Hysteresis
Safety/Protection Features
nOvervoltage Protection Against Open Current and Open Voltage Loop
nProtection Against Short Circuit on Oscillator Pin
nFully Programmable Foldback
nSoft-Start Feature
nAccurate Maximum Duty Cycle Setting
nDemagnetization (Zero Currrent Detection) Protection
nInternally Trimmed Reference
GreenLine Controller: Low Power Consumption in Standby Mode
nLow Startup and Operating Current
nFully Programmable Standby Mode
nControlled Frequency Reduction in Standby Mode
nLow dV/dT for Low EMI Radiations.
PINNING
1- VCCThis pin is the positive supply of the IC. The operating voltage range after startup is 9.0 to 14.5V.
2- VCThe output high state (V) is set by the voltage applied to this pin.
OH
With a separate connection to the power source, it can reduce the efffects of switching noise on the control circuitry.
3- OUTPUTPeak currents up to 750mA can be sourced or sunk, suitable for driving either MOSFET or
Bipolar transistör. This output pin must be shunted by a Schottky diode, 1N5819 or equivalent.
4- GNDThe ground pin is a single return, typically connected back to the power source;it is usedas control and power ground.
5- Foldback InputThe foldback function provides overload protection. Feeding the foldback input with aportion of
the VCC voltage (1.0V max) establishes on the system control loop a foldback characteristic
allowing a smoother startup and sharper overload protection. Above 1.0V foldback input is inactive.
6- Overvoltage Protection When the overvoltage protection pin receives a voltage greater than 17V, the device is
disabled and requires a complete restart sequence. The overvoltage level is programmable.
7- Current Sense InputA voltage proportional to the current flowing in to the power switch is connected to this input.
The PWM latch uses this information to terminate the conduction of the output buffer when working in a corrent mode
of operation. A maximum level of 1.0V allows either current or voltage mode of operation.
8- DemagnetizationA voltage delivered by an auxiliary transformer winding provides to the demagnetization pin an
Detectionindication of the magnetization state of the flyback transformer. A zero voltage detection corresponds to complete
core saturation. The demagnetization detection ensures a discontinuous mode of opertion.
This function can be inhibited by connecting Pin 8 to Gnd.
9- Synchronization InputThe synchronization input pin can be activated with either a negative pulse going from a level between 0.7V and 3.7V
to Gnd or a positive pulse going from a level between 0.7 and 3.7V up to a level higher than 3.7V. The oscillator runs
free when Pin 9 is connected to Gnd.
10- CTThe normal mode oscillator frequency is programmed by the capacitor CT choice together with the Rref resistance
value. CT, connected between Pin 10 and Gnd, generates the oscillator sawtooth.
11- Soft-Start/DmaxA capacitor, resistor or a voltage source connected to this pin limits The switching duty-cycle.
/Voltage-ModeThis pin can be used as a voltage mode control input. By connecting Pin11 to Ground,
the MC44603 can be shut down.
12- RP StandbyA voltage level applied to the RP Standby pin determines the output power level at which the oscillator will turn into the
reduced frequency mode of operation (i.e. standby mode).
An internal hysteresis comparator allows to return in the normal mode at a higher output power level.
13- E/A OutThe error amplifier output is made avaliable for loop compensation.
14- Voltage FeedbackThis is the inverting input of the Error Amplifier. It can be connected to the switching power supply output through
an optical (or other) feedback loop.
15- RF StandbyThe reduced frequency or standby frequency programming is made by the RF Standby resistance choice.
16-RrefRref sets the internal reference current. The internal reference current ranges from 100?A to 500 ?A.
This requires that 5.0kW < Rref < 25 kW.
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ACEC
