UM2640

CMOS IC

UNISONIC TECHNOLOGIES CO., LTD

7 of 8

www.unisonic.com.tw

QW-R109-027.D



APPLI CAT I ON I N FORM AT I ON (Cont .)

7. Design of C2:

Lock Protection Function, consists of Motor Lock Detection and Auto Resume Function, is a safety feature to

protect a motor and a driver circuit from fatal destruction in case of motor halt.

Motor Lock Detection detects motor halt due to irregular load conditions and then cuts motor driving current for

safety operation. When Lock Detection is activated; Lock Alert Out (LA: Pin 3) goes to L.

A value of C2 determines Lock detection time (Ton) and Auto Resume Time (Toff).

Lock detection time (Ton) is given by:

[sec]

Ic

Vcl

-

Vch

2

C

=

T

ON

Where C2 is 0.47uF:

[sec]

22

.

0

=

10

×

8

.

3

7

.

0

-

5

.

2

×

10

×

47

.

0

=

T

6

-

6

-

ON

Auto Resume Time (Toff) is given by:

[sec]

Idc

Vcl

-

Vch

2

C

=

T

OFF

Where C2 is 0.47uF:

[sec]

13

.

1

=

10

×

75

.

0

7

.

0

-

5

.

2

×

10

×

47

.

0

=

T

6

-

6

-

OFF

A typical value of C2 is either 0.47uF or 1uF depending on a motor.

Lock Protection

Lock Alert Out (LA: Pin 3) is a open collector output and R3 is a pull up resister. A typical value of R3 is 10k

Ω.

It must be noted that Lock Alert Out stays an H state during few hundred milliseconds from power up as shown in

the picture below.