UCC28180
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SLUSBQ5A –NOVEMBER 2013–REVISED NOVEMBER 2013
Sense Resistor
To accommodate the gain of the non-linear power limit, the sense resistor, RSENSE, is sized such that it triggers
the soft over current at 10% higher than the maximum peak inductor current using the minimum soft over current
threshold of the ISENSE pin, VSOC, of ISENSE equal to 0.265 V.
VSOC(min)
RSENSE
=
I
L _ PEAK(max) ´1.1
(50)
(51)
0.259 V
RSENSE
=
= 0.032W
7.7 A ´1.1
The power dissipated across the sense resistor, PRSENSE, must be calculated:
PRSENSE = II2N_ RMS(max)RSENSE
(52)
(53)
PRSENSE = 4.551A2 ´0.032W = 0.663W
The peak current limit, PCL, protection feature is triggered when current through the sense resistor results in the
voltage across RSENSE to be equal to the VPCL threshold. For a worst case analysis, the maximum VPCL threshold
is used:
VPCL(max)
IPCL
=
RSENSE
(54)
(55)
0.438 V
IPCL
=
= 13.688 A
0.032W
To protect the device from inrush current, a standard 220-Ω resistor, RISENSE, is placed in series with the ISENSE
pin. A 1000-pF capacitor is placed close to the device to improve noise immunity on the ISENSE pin.
Copyright © 2013, Texas Instruments Incorporated
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