Philips CDR570, Service Manual

Page: 48 / 59

Faultfinding Guide GB 48 CDR570/930 8.
Pin function description
Figure 8-20
Block diagram of MC44603
Figure 8-21
Pin Name Description
1 VCC This pin is the positive supply of the IC. The operating voltage range after start-up is 9.0 to 14.5 V.
2 VC The output high state (VOH) is set by the voltage applied to this pin.
3 Output Peak currents up to 750 mA can be sourced or sunk, suitable for driving either MOSFET or bipolar transistors.
4 Gnd The groundpin is a single return, typically connected back to the power source.
5 Foldback Input The foldback function provides overload protection.
6 Overvoltage
Protection When the overvoltage protection pin receives a voltage greater than 2.5V, the device is disabled and requires a
complete restart sequence.
7 Current Sense
Input A voltage proportional to the current flowing into the power switch is connected to this input.
8 Demagnetisation
Detection A voltage delivered by an auxiliary transformer winding provides to the demagnetisation pin an indication of the
magnetisation state of the flyback transformer. A zero voltage detection corresponds to complete core
saturation.
9 Synchronisation
Input The synchronisation 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 0.7V and 3.7V up to a level higher than 3.7V. The
oscillator runs free when Pin 9 is connected to Gnd.
10 C
T
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/Volta
ge-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 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 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 RF Standby The reduced frequency or standby frequency programming is made by the RF Standby resistance choice.
16 Rref
Rref sets the internal reference current. The internal reference current ranges from 100
µ
A to 500
µ
A. This
requires that 5.0k
Ω ≤
Rref
≤
25k
Ω
.
CL 96532076_031.eps
290799
VS8 OUT
CONTROL
Dmax &
SOFT-START
Vref
Voc
GND
OUT
VC
PROTECT
VOLTAGE
OVER
MANAGEMENT
OVER
VOLTAGE
DEMAGNETISATION
MANAGEMENT
OSCILLATOR
STANDBY
(REDUCED FREQUENCY)
ERROR
AMP
CURRENT
SENSE
DEMAGNETISATION
DETECT
SYNC INPUT
CT
RF STANDBY
Iref
REFERENCE
BLOCK
SUPPLY
INITIALISATION BLOCK
Vref Iref
Vref
enable
UVL01
VOSC
VOSC PROT
=1
LATCH
THERMAL
SHUTDOWN
BUFFER
VOLTAGE
FEEDBACK
2.5V
RP STANDBY
Iref
UVL01
Vref
FOLDBACK
FOLDBACK
INPUT CURRENT SENSE
INPUT
SOFT-START
& DMAX
1
2
3
4
6
5 7 11
8
9
10
15
12
14
13
E/A OUT
16
C
1Set
1Reset
Vstby
CL 96532076_032.eps
290799
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