M51995AP/AFP

REJ03D0835-0300 Rev.3.00 Jun 06, 2008

Page 26 of 40

ON/OFF

30 k to 100 k

Ω

M51995A

Figure 18 Connecting of ON/OFF Terminal

1.6

1.2

0.8

0.4

0

0

5

10

15

20

25

30

OVP Circuit (Over Voltage Protection Circuit) Section

OVP circuit is basically positive feedback circuit constructed by Q2, Q3 as shown in figure 20.

Q2, Q3 turn on and the circuit operation of IC stops, when the input signal is applied to OVP terminal. (threshold

voltage

≈ 750 mV)

The current value of I2 is about 150

µA when the OVP does not operates but it decreases to about 2 µA when OVP

operates.

It is necessary to input the sufficient larger current (800

µA to 8 mA) than I2 for triggering the OVP operation.

It is necessary that OVP state holds by circuit current from R1 in the application example, so this IC has the

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 21.

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.

So if the capacitor is connected between the OVP terminal and GND, even though Q2 turns on in a moment by the

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