LB11850VA

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13

<LIM Pin>

The minimum speed is determined by the voltage of the LIM pin.

Figure 13.

(RPM)

CTL Duty(%)

Maximum speed

0%

5 V

100%

2 V

Minimum

speed setup

CVO pin voltage (V)

2000

4000

6000

8000

10000

1) Obtain the ratio of the minimum speed required to the maximum speed.

Ra = Minimum speed/maximum speed .... <1>

In the example shown in the figure above, Ra = minimum speed/maximum speed = 3000/10000 = 0.3.

2) Obtain the product of the duty ratio at which the maximum speed is obtained and the value in equation <1>.

Ca = Duty ratio at maximum speed

× Ra .... <2>

In this example, Ca = duty ratio at maximum speed

× Ra = 0.8 × 0.3 = 0.24.

3) Obtain the required LIM pin voltage.

LIM = 5 − (3

× Ca) .... <3>

In this example, LIM = 5 − (3

× Ca) = 5 − (3 × 0.24) ≈ 4.3 V.

4) Divide the resistance of 5VREG, and generate the LIM voltage.

In this example, the voltage is 4.3 V so the resistance ratio is 1 : 6.

The resistance is 10 k

W between 5VREG and LIM and 62 kW between LIM and GND.

Figure 14.

5VREG

VREF

CVI

SOFT

LIM