Philips Semiconductors

PIP401

OR-ing Intelligent Switch

Product data

Rev. 03 — 5 November 2002

4 of 16

9397 750 10578

© Koninklijke Philips Electronics N.V. 2002. All rights reserved.

7.3 Driver and series power switch

7.3.1

Soft turn-on

At switch on, the PIP401 turns on slowly to avoid current surges. These can cause

oscillations in the output voltage and may cause the protected power supply to shut

down. Typical turn-on time is 7

µs.

7.3.2

Low voltage drop

The on-state characteristic of the PIP401 is shown in Figure 5. In the on-state, the

PIP401 has very low voltage drop, typically 70 mV at 40 A, 25

°C. This produces a

power dissipation of 2.8 W. In comparison, a Schottky diode with a forward voltage

drop of 320 mV would have a power dissipation of 12.8 W.

7.3.3

Low current operation

At low current levels, the voltage drop is only a few millivolts. This makes it difficult for

the comparator to determine when to switch off. The PIP401 overcomes this problem

by backing off the gate drive to the series power switch at current levels below 2 A.

The effect is to increase the resistance between VI and VO so that the voltage drop is

maintained at a constant level of approximately 6 mV. This is above the minimum

detectable threshold voltage of the comparator. This is shown in Figure 5 by the

flattening of the curves at low current.

7.3.4

Fast turn-off with no reverse current

PIP401 switches off very quickly, blocking the flow of reverse current. Figure 3 shows

switching waveforms from an initial forward current of 20 A. Note the smooth ramp

down of current from 20 A with no reverse current flow and minimum disruption of the

output voltage. Total turn-off time is less than 400 ns.

The gate drive circuit in the PIP401 is referenced to VI. When the input voltage is less

current is 35 mA. In order to prevent charging of the output capacitors of the

protected supply connected to VI, a 100 W resistor should be connected between VI

and GND. This is shown as R1 in Figure 2.