m51996ap Renesas Electronics Corporation., m51996ap Datasheet - Page 20

• Manufacturer Part Number: m51996ap
• Description: Switching Regulator Control
• Manufacturer: Renesas Electronics Corporation.

M51996AP/AFP
OVP Circuit (Over Voltage Protection Circuit) Section
OVP circuit is basically positive feedback circuit constructed by Q2, Q3 as shown in figure 13.
Q2, Q3 turn on and the circuit operation of IC stops, when the input signal is applied to OVP terminal. (threshold
voltage
The current value of I2 is about 150 A when the OVP does not operates but it decreases to about 2 A when OVP
operates.
It is necessary to input the sufficient larger current (800 A to 8 mA) than I2 for triggering the OVP operation.
The reason to decrease I2 is that it is necessary that I
It is necessary that OVP state holds by circuit current from R1 in the application example, so this IC has the
characteristic of small I
On the other hand, the circuit current is large in the higher supply voltage, so the supply voltage of this IC doesn’t
become so high by the voltage drop across R1.
This characteristic is shown in figure 14.
The OVP terminal input current in the voltage lower than the OVP threshold voltage is based on I2 and the input current
in the voltage higher than the OVP threshold voltage is the sum of the current flowing to the base of Q3 and the current
flowing from the collector of Q2 to the base.
For holding in the latch state, it is necessary that the OVP terminal voltage is kept in the voltage higher than V
So if the capacitor is connected between the OVP terminal and GND, even though Q2 turns on in a moment by the
surge voltage, etc, this latch action does not hold if the OVP terminal voltage does not become higher than V
by charging this capacitor.
For resetting OVP state, it is necessary to make the OVP terminal voltage lower than the OVP L threshold voltage or
make V
As the OVP reset voltage is settled on the rather high voltage of 9.0 V, SMPS can be reset in rather short time from the
switch-off of the AC power source if the smoothing capacitor is not so large value.
REJ03D0836-0201 Rev.2.01 Nov 14, 2007
Page 20 of 35
CC
750 mV)
lower than the OVP reset supply voltage.
CC
at the OVP reset supply voltage ( stand-by current
Figure 13 Detail Diagram of OVP Circuit
GND
OVP
Note: I
V
CC
1
= 0 when OVP operates
12 k
8 k
CC
I
2
at the OVP rest supply voltage is small.
7.8 V
400
Q1
Q2
2.5 k
Q3
I
1
100 µA
20 A)
BE
BE
of Q3
of Q3.