WT7527V
Rev. 1.01
APPLICATION NOTE
IL
V12A
+
VL
-
V12A
RL
R
VS
IS
-
OCP
+
V12A
IREF
+
VR
-
VREF = 1.2V
+
-
IR=8*IREF=8* ( VREF/RI )
IR
RI
IREF=VREF / RI
RI
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 ≥ 1uF is suggested.
OCP point can be calculated by the following equation:
Let VR = VL
R × IR = RL × IL
VREF
Q IR = 8× IREF = 8×
RI
RL× IL
∴R =
VREF
8×
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.
Page 8
WELTREND [ WELTREND SEMICONDUCTOR ]
