7
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. Its advanced design allows use in current
mode or voltage mode control applications.
FEATURES :
Current or Voltage Mode Controller
n
Operation up to 250 kHz Output Switching Frequency
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I
nherent Feed Forward Compensation
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Latching PWM for Cycle-by-Cycle Current Limiting
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Oscillator with Precise Frequency Control
High Flexibility
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Externally Programmable Reference Current
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Secondary or Primary Sensing
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Synchronization Facility
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High Current Totem Pole Output
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Undervoltage Lockout with Hysteresis
Safety/Protection Features
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Overvoltage Protection Against Open Current and Open Voltage Loop
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Protection Against Short Circuit on Oscillator Pin
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Fully Programmable Foldback
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Soft-Start Feature
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Accurate Maximum Duty Cycle Setting
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Demagnetization (Zero Currrent Detection) Protection
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Internally Trimmed Reference
GreenLine Controller: Low Power Consumption in Standby Mode
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Low Startup and Operating Current
n
Fully Programmable Standby Mode
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Controlled Frequency Reduction in Standby Mode
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Low dV/dT for Low EMI Radiations.
PINNING
1- VCC
This pin is the positive supply of the IC. The operating voltage range after startup is 9.0 to 14.5V.
2- VC
The output high state (V
OH
) is set by the voltage applied to this pin.
With a separate connection to the power source, it can reduce the efffects of switching noise on the control circuitry.
3- OUTPUT
Peak 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- GND
The ground pin is a single return, typically connected back to the power source;it is usedas control and power ground.
5- Foldback Input
The 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 Input
A 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- Demagnetization
A voltage delivered by an auxiliary transformer winding provides to the demagnetization pin an
Detection
indication 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 Input
The 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- CT
The 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/Dmax
A capacitor, resistor or a voltage source connected to this pin limits The switching duty-cycle.
/Voltage-Mode
This pin can be used as a voltage mode control input. By connecting Pin11 to Ground,
the MC44603 can be shut down.
12- RP Standby
A 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 Out
The error amplifier output is made avaliable for loop compensation.
14- Voltage Feedback
This 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 Standby
The reduced frequency or standby frequency programming is made by the RF Standby resistance choice.
16-R
ref
R
ref
sets the internal reference current. The internal reference current ranges from 100µA to 500 µA.
This requires that 5.0k
W <
R
ref
<
25 k
W.
