LB11852FV

No.A1112-10/12

4. Procedure for calculating the constant

〈RC pin〉

The slope shown in the speed control diagram is determined by the constant of the RC pin.

1) Obtain the FG signal frequency fFG (Hz) at the maximum rotational speed of the motor

(with two FG pulses per rotation).

fFG (Hz) = 2 rpm/60 … (1)

2) Obtain the time constant of the components connected to the RC pin

(use the duty ratio (example : 100% = 1.0 or 60% = 0.6) as the CTL duty ratio for achieving the maximum rotational

speed).

R

× C = Duty ratio/ (3.3 × 1.1 × fFG) … (2)

3) Obtain the resistance and the capacitance of the capacitor.

Based on the discharge capability of the RC pin, the capacitance of the capacitor which can be used is in the range of

0.01

μF to 0.015μF.

Therefore, obtain the appropriate resistance from the result of (2) above using the formula in (3) or (4) below.

R = (R

× C)/0.01μF … (3)

R = (R

× C)/0.015μF … (4)

The temperature characteristics of the curve are determined by the temperature characteristics of the capacitor of the

RC pin. To minimize the variations in the rotational speed caused by temperature, a capacitor with excellent

temperature characteristics must be used.

(RPM)

Motor

at maximum speed

0%

100%

CTL Duty(%)