MC44603P Просмотр технического описания (PDF) - ON Semiconductor
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MC44603P Datasheet PDF : 22 Pages
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MC44603A
270
265
260
255
250
245
VR P Stdby (Pin 12)
Voltage Increasing
240
235
230
−50
−25
0
25
50
75
100
TA, AMBIENT TEMPERATURE (°C)
Figure 26. Standby Reference Current
versus Temperature
0.33
0.32
0.31
VCC = 12 V
Rref = 10 k
CT = 820 pF
Pin 12 Clamped
at 1.0 V
0.30
−50
−25
0
25
50
75
100
TA, AMBIENT TEMPERATURE (°C)
Figure 27. Current Sense Voltage Threshold
Standby Mode versus Temperature
PIN FUNCTION DESCRIPTION
Pin
Name
Description
1
VCC
This pin is the positive supply of the IC. The operating voltage range after startup is 9.0 to 14.5 V.
2
VC
The output high state (VOH) 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.
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 The foldback function provides overload protection. Feeding the foldback input with a portion of the VCC
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 When the overvoltage protection pin receives a voltage greater than 17 V, the device is disabled and
Protection
requires a complete restart sequence. The overvoltage level is programmable.
7
Current Sense A voltage proportional to the current flowing into the power switch is connected to this input. The PWM latch
Input
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 A voltage delivered by an auxiliary transformer winding provides to the demagnetization pin an indication of
Detection
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 The synchronization input pin can be activated with either a negative pulse going from a level between 0.7 V
Input
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
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. This pin can
Voltage−Mode be used as a voltage mode control input. By connecting Pin 11 to Ground, the MC44603A can be shutdown.
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
This is the inverting input of the Error Amplifier. It can be connected to the switching power supply output
Feedback
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 mA to 500 mA. This
requires that 5.0 kW ≤ Rref ≤ 25 kW.
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11
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