M61558FP

Rev.1.0, Sep.19.2003, page 12 of 17

Internal protective circuits

1. VDD under voltage detection circuit

When the VDD power-supply voltage falls by a certain amount, the VDD under voltage protective circuit operates

to prevent malfunctions of the IC. When an abnormality is detected, the output transistor on the H side is switched

off, the output transistor on the L side is switched on, and a low level is output from the output pin. For the sake of

automatic resumption, a low level is not output from PROUT (pin 21). Of the protection states, this is only the case

for abnormal voltage-drop detection. The VDD detection circuit is connected to the common VDD power-supply

pin, VDDP (pin 20). Please set up IC-external wiring to connect the VDDA/B (pins 12, 30) to VDDP.

2. Over Temperature protection circuit

The IC incorporates an over temperature protection circuit (thermal shutdown circuit) that protects the IC from

thermal damage when the temperature of the IC (chip) rises because of an abnormality. The protection circuit is

activated before the IC’s internal junctions, etc., reach the thermal-damage temperature, and remains so until the

temperature falls to the hysteresis condition, regardless of the state of the EN pin (pin 25). In the excessive-

temperature condition, all output transistors are turned off, the output pins are released (open), and a low level is

output from PROUT to issue a notification about the abnormal state.

3. Over current protection circuit

This IC incorporates an excessive current protection circuit which terminates the PWM operation when the peak

instantaneous value of current supplied from the VDA or VDB power supply exceeds 7.5 A (designed value). In the

protection mode, all output transistors are switched off, all output pins are released (open), and a low level is output

from PROUT to notify the system of the abnormal state.

Note: The abnormality is detected on the positive side of the power-stage power supply. The conditions for

detecting a load short between output pin and VDD. VDD are not more strict short between both output

pins or between output pin and ground. Note that when shorting between VDD occurs, detection is not

possible until the abnormality affects the positive side of the power supply, so the protective operation

may not be performed.

Functions when an abnormality is detected

When an abnormality is detected, the IC operates asynchronously with respect to the PWM inputs (INA+, INB+),

controls the output-stage n-channel transistor (H or L side) and enters the protection state. The states of the PROUT and

OUT outputs and the states of each output-stage transistor are given in the table below. After the low level has been

placed on PROUT, the protection state is maintained until the EN signal is low.

State of output stage during protection operation

OUTA output-

stage transistor

OUTB output-

stage transistor

Protection

PROUT output in case of

abnormality

OUTA

output pin

OUTB

output pin

H side

L side

H side

L side

VDD voltage-drop

protection

No change (high)

Low

Low

Off

On

Off

On

Over

Temperature,

over-current

protection

Output low, held until low

level is placed on EN

Open

Open

Off

Off

Off

Off

Resuming from abnormality detection

Resumption to signal output from the individual abnormal state varies with the corresponding protective circuit. After

the conditions for resumption have been satisfied, resumption occurs on the rising edge of either INA+ or INB+,

whichever is earlier. The conditions for resumption from each abnormal state are given in the table below.