APPLICATION NOTE
WT7527
Rev. 1.20
When the load current increased, the voltage (VL) cross the inductor is increased.
And when inductor voltage exceeds the resistor voltage (VR), the OCP is active.
Sometimes power-on or load dynamics will cause false output of over-current detection. It can be
solved by connecting a capacitor between VS pin and IS pin. In typical case, C ≥ 0.47uF is suggested.
OCP point can be calculated by the following equation:
Let VR = VL
R × IR = RL × IL
Q IR = 8 × IREF = 8 × VREF
RI
∴
R
=
RL × IL
8 × VREF
RI
For example:
Assume RI=30KΩ, RL=5mΩ, OCP IL=20A.
Sol:R = ( IL * RL ) / ( 8 * IREF )
= ( 20A * 5mΩ) / { 8 * ( 1.2V / 30KΩ)}
= 312.5Ω
Weltrend Semiconductor, Inc.
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