M63151FP

Rev.1.0, Sep.16.2003, page 8 of 13

Motor-Lock Protection Circuit (1)

As well as the overheating protection function, this IC incorporates a module that turns off current to the motor after the

motor has been mechanically held over a specified period. This prevents overheating. The operating conditions of this

module and a timing chart that depicts its operation are given below. Note, however, that when the IC does become

overheated, the overheating protection circuit still operates because it takes precedence over the lock protection

function.

(1) Conditions of operation

(a) The RS current detection resistor detects a continuous flow of the limit current (in practice, the current-limiting

circuit leaves the IC operating as long as the voltage on RS stays within the range 0 to 0.25 V).

(b) Normally, the period at 0 V in item (a) will be 3.5

µs, and this is approximately equal to the period at 0.25 V.

However, this circuit does not operate when motor characteristics, etc. mean that the period at 0.25 V is three times

the period at 0 V (duty cycle = 75%) or longer.

(c) The period of the lock-protection circuit operations (the period from locking of the motor to the time when current

to the motor is stopped) is determined by the time constant set up by the capacitor and resistor externally connected

to pins 37 (CRLP) and 38 (RLP).

(d) After the motor has been turned off, automatic resumption is attempted at a time determined by the same R and C

values as in point (c). External signals are not accepted until resumption.

(2) Block diagram

+

-

+

-

+

-

0.25V

1V

Hi: PWM-ON

Lo: PWM-OFF

(Regeneration)

4V

5.4V

or

1.2

Hi: Normal operation

Lock protection

circuit control signal

Low: MOTOR - lock protection circuit

17

38

37

VREG(6V)

VREG

Comp1

Comp2

Comp3

Comp4

A

0

0.25V

Current limiting

control signal

5.4V

1.2V

POINT A

RNF

RFP

CRLP

CRLP

RNF

Comp3 output

1V

0

0.7V

4V

C=1

µF

R=4.7M

C1

↓I1

Ω

Current - Limiting

control signal

Lock protection circuit

control signal

Currnt flows to

the motor

Flow of current to

the motor stops

Currnt flows to

the motor

↑Initiation

When the maximum current no longer flows to the RNF,

the CRLP voltage is driven low to cancel the protective finction.