IRS20124S(PbF)
threshold level is being set. Please also note that,
in the negative load current direction, the sensing
voltage at the Vs node is limited by the body di-
ode of the low side MOSFET as explained later.
>0.5mA
Vcc
R3
OCSET1
OCSET2
COM
Design Example
R4
R5
This example demonstrates how to use the ex-
ternal? resistor network to set ITRIP+ and ITRIP- to
be ±11A, using a MOSFET that has RDS(ON)
=60mÙ.
VISET1 = VTH+ + 2.21 = ITRIP+ x RDS(ON) + 2.21= 11
x 60mÙ +2.21 = 2.87V
Figure 12. External Resistor Network to set OC
Threshold
VISET2 = VTH- + 2.21 = ITRIP- x RDS(ON) + 2.21= (-11)
x 60mÙ +2.21 = 1.55V
How to set OC Threshold
The total resistance of resistor network is based
on the voltage at the Vcc and required bias cur-
rent in this resistor network.
The positive and negative trip thresholds for bi-
directional current sensing are set by the voltages
at OCSET1 and OCSET2. Fig.14 shows a typical re-
sistor voltage divider that can. be used to set
Rtotal =R3 + R4 + R5 = Vcc / Ibias
OCSET1 and OCSET2
.
= 12V / 1mA = 12KÙ
The trip threshold voltages, VSOC+ and VSOC+, are
determined by the required trip current levels, ITRIP+
andITRIP-, and RDS(ON) in the low side MOSFET.
Since the sensed voltage of Vs is shifted up by
2.21V internally and compared with the voltages
fed to the OCSET1 and OCSET2 pins, the required
value of OCSET1 with respect to COM is
The expected voltage across R3 is Vcc- VISET1
= 12-2.87=9.13V. Similarly, the voltages across
R4 is VSOC+ - VSOC- = 2.87-1.55=1.32V, and the
voltage across R5 is VISET2= 1.55V respectively.
R3 =9.13V/ Ibias = 9.13KÙ
R4 =1.32V/ Ibias = 1.32KÙ
R5 =1.55V/ Ibias = 1.55KÙ
V
OCSET1 = VSOC+ + 2.21 = ITRIP+ x RDS(ON) + 2.21
Choose R3= 9.09KÙ, R4=1.33KÙ, R5=1.54KÙ
from E-96 series.
Consequently, actual threshold levels are
VSOC+ =2.88V gives ITRIP+ = 11.2A
VSOC- =1.55V gives ITRIP- = -11.0A
The same relation holds between OCSET2 andVSOC-,
VOCSET2 = VSOC- + 2.21 = ITRIP- x RDS(ON) + 2.21
In general, R
has a positive temperature co-
efficient thatDnSe(OeN)ds to be considered when the
Resisters with 1% tolerances are recommended.
www.irf.com
23
INFINEON [ Infineon ]
