mc44603 ON Semiconductor, mc44603 Datasheet - Page 10

• Manufacturer Part Number: mc44603
• Description: Mixed Frequency Mode Greenline Pwm Controller
• Manufacturer: ON Semiconductor

10
270
265
260
255
250
245
240
235
230
Pin
10
11
12
13
14
15
16
1
2
3
4
5
6
7
8
9
–50
Figure 25. Standby Reference Current
V CC
V C
Output
Gnd
Foldback Input
Overvoltage
Protection
Current Sense
Input
Demagnetization
Detection
Synchronization
Input
C T
Soft–Start/D max /
Voltage–Mode
R P Standby
E/A Out
Voltage Feedback
R F Standby
R ref
–25
Name
T A , AMBIENT TEMPERATURE ( C)
versus Temperature
0
25
This pin is the positive supply of the IC. The operating voltage range after startup is 9.0 to 14.5 V.
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 effects of switching noise on the control circuitry.
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.
The ground pin is a single return, typically connected back to the power source; it is used as control and
power ground.
The foldback function provides overload protection. Feeding the foldback input with a portion of the V CC
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.
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.
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.
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.
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.
The normal mode oscillator frequency is programmed by the capacitor C T choice together with the R ref
resistance value. C T , connected between Pin 10 and Gnd, generates the oscillator sawtooth.
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 MC44603 can be
shut down.
A voltage level applied to the R P 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.
The error amplifier output is made available for loop compensation.
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.
The reduced frequency or standby frequency programming is made by the R F Standby resistance choice.
R ref sets the internal reference current. The internal reference current ranges from 100 µA to 500 µA.
This requires that 5.0 kΩ
V R P Stdby (Pin 12)
Voltage Increasing
50
PIN FUNCTION DESCRIPTION
75
MC44603
R ref
100
25 kΩ.
0.33
0.32
0.31
0.30
–50
Description
Figure 26. Current Sense Voltage Threshold
Standby Mode versus Temperature
–25
MOTOROLA ANALOG IC DEVICE DATA
T A , AMBIENT TEMPERATURE ( C)
0
25
V CC = 12 V
R ref = 10 k
C T = 820 pF
Pin 12 Clamped
at 1.0 V
50
75
100