lb11850va Sanyo Semiconductor Corporation, lb11850va Datasheet - Page 13

• Manufacturer Part Number: lb11850va
• Description: For Fan Motor Single-phase Full-wave Pre-driver With Speed Control Function
• Manufacturer: Sanyo Semiconductor Corporation

<LIM pin>
The minimum speed is determined by the voltage of the LIM pin.
(1) Obtain the ratio of the minimum speed required to the maximum speed.
(2) Obtain the product of the duty ratio at which the maximum speed is obtained and the value in equation <1>.
(3) Obtain the required LIM pin voltage.
(4) Divide the resistance of 5VREG, and generate the LIM voltage.
Ra = Minimum speed/maximum speed .... <1>
In the example shown in the figure above, Ra = minimum speed/maximum speed = 3000/10000 = 0.3.
Ca = Duty ratio at maximum speed×Ra .... <2>
In this example, Ca = duty ratio at maximum speed×Ra = 0.8×0.3 = 0.24.
LIM = 5-(3×Ca) .... <3>
In this example, LIM = 5-(3×Ca) = 5-(3×0.24) ≈ 4.3V.
In this example, the voltage is 4.3V so the resistance ratio is 1: 6.
The resistance is 10kΩ between 5VREG and LIM and 62kΩ between LIM and GND.
Maximum speed
Minimum
speed setup
(RPM)
10000
8000
6000
4000
2000
0%
5V
5VREG
SOFT
LIM
CVI
LB11850VA
CVO pin voltage (V)
VREF
CTL Duty(%)
No.A0609-13/14
100%
2V