(2) CR time constant setting method

1 Bias current of CR pin and effect of leakage of C. The value of the charge current at the threshold point is V

0.2/R3. Therefore, this value and the leakage of C must be large enough for the bias current.

2 The CR pin voltage must not exceed 0.6 × V

rotational speed of a fan is reached and while a fan keeps the normal rotational speed; a malfunction may be caused by

instantaneous drop of power supply.

3 It should be noted that the CR pin voltage is varied with the combination C and R, even if the CR time constant is the

same.

The allowable CR setting value is given in the diagram.

(3) Restart after lock detection

The LB1660 series are so designed that when motor lock

is detected and the output stage transistor is turned off the

drive-off state is kept even after motor lock is released.

The method of restart is shown below.

1 Turn off the power supply and turn on again. Turn

2 Set the CR pin voltage to be less than 1 V, and then

turn off the power supply in order to cause the lock

detect function to return to normal. (The CR pin can

be also used to provide on-off control.)

Output transistor lock

Pulse of 1

Pulse of 2

Generation of discharge pulse

t–R

Resistance, R –

Ω

LB1660N, 1661, 1664N, 1665

No.2551-8/9