lb11852fv Sanyo Semiconductor Corporation, lb11852fv Datasheet - Page 11

• Manufacturer Part Number: lb11852fv
• 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 achieved and the value in formula (1).
3) Obtain the required LIM pin voltage.
4) Divide the resistance of 5VREG to generate the LIM voltage.
Ra = Minimum/maximum speed … (1)
In the example shown in the figure above : Ra = minimum/maximum speed = 3000/10000 = 0.3
Ca = Maximum speed duty ratio × Ra … (2)
In the example given : Ca = maximum speed duty ratio × Ra = 0.8 × 0.3 = 0.24
LIM = 5 - (3 × Ca) … (3)
In the example given : LIM = 5 - (3 × Ca) = 5 - (3 × 0.24) ≈ 4.3V
In the example given, 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
LB11852FV
LIM
SOFT
CVI
CTL Duty(%)
CVO pin voltage (V)
VREF
100%
2V
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