LB11850VA Datasheet, PDF (13/14 Pages) Sanyo Semicon Device – Monolithic Digital IC For Fan Motor Single-Phase Full-Wave Pre-Driver with Speed Control Function

LB11850VA
<LIM pin>
The minimum speed is determined by the voltage of the LIM pin.
(RPM)
Maximum speed ¹⁰⁰⁰⁰
8000
6000
4000
Minimum
speed setup ²⁰⁰⁰
0%
CTL Duty(%)
5V
CVO pin voltage (V)
100%
2V
(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) ≈ 4.3V.
(4) Divide the resistance of 5VREG, and generate the LIM voltage.
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.
5VREG
LIM
SOFT
CVI
VREF
No.A0609-13/14