MC44603A

http://onsemi.com

11

−50

−25

0

25

50

75

100

Figure 26. Standby Reference Current

versus Temperature

Figure 27. Current Sense Voltage Threshold

Standby Mode versus Temperature

−50

−25

0

25

50

75

100

270

260

250

240

230

0.33

0.32

0.31

0.30

265

255

245

235

Voltage Increasing

Pin 12 Clamped

at 1.0 V

PIN FUNCTION DESCRIPTION

Pin

Name

Description

1

This pin is the positive supply of the IC. The operating voltage range after startup is 9.0 to 14.5 V.

2

source, it can reduce the effects of switching noise on the control circuitry.

3

Output

Peak currents up to 750 mA can be sourced or sunk, suitable for driving either MOSFET or Bipolar

transistors. 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 used as control and

power ground.

5

Foldback Input

voltage (1.0 V max) establishes on the system control loop a foldback characteristic allowing a smoother

startup and sharper overload protection. Above 1.0 V the foldback input is inactive.

6

Overvoltage

Protection

When the overvoltage protection pin receives a voltage greater than 17 V, 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 into 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 current mode of

operation. A maximum level of 1.0 V allows either current or voltage mode operation.

8

Demagnetization

Detection

A voltage delivered by an auxiliary transformer winding provides to the demagnetization pin an 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 operation. 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 0.7 V

and 3.7 V to GND or a positive pulse going from a level between 0.7 V and 3.7 V up to a level higher than

3.7 V. The oscillator runs free when Pin 9 is connected to GND.

10

11

Voltage−Mode

A capacitor, resistor or a voltage source connected to this pin limits the switching duty−cycle. This pin can

be used as a voltage mode control input. By connecting Pin 11 to Ground, the MC44603A can be shutdown.

12

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 available 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

16

requires that 5.0 k