Document Number: 73868

S11-0975–Rev. C, 16-May-11

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9

Vishay Siliconix

SiP11203, SiP11204

This document is subject to change without notice.

“swaps” the synchronous rectifier drive paths. This

causes the high-going signal on INB to be applied

to the gate of an n-channel hold-off MOSFET,

which is in parallel with the main OUTA driver. This

MOSFET inverts the signal from INB, which causes

its drain to be pulled towards ground. This holds

OUTA low.

• During the deadtime in which neither INB nor INA is

driven high, the voltage on INA and that on INB will

both OUTA and OUTB being pulled low by their

associated inverter MOSFETs.

• During the next cycle of converter operation, all of

the above applies with the exception that INB is

now driven low, which will cause INA to be driven

high. This will in turn cause the hold-off MOSFET in

parallel with the main OUTB driver to conduct,

thereby holding OUTB low.

In this way, the SiP11203/SiP11204 “swap and invert”

function prevents any unwanted turn-on of the

reaches 90 % of its final value, the drive path inside the

IC is no longer swapped, and the inverting hold-off

MOSFETs are disabled.

FUNCTIONAL BLOCK DIAGRAM

START-UP DRIVER OPERATION

voltage greater than 5.5 V, the factors controlling the

value and the pre-regulator’s current limit. This gives

the following two equations:

• The time from start-up to

• The time from start-up to

1.1 V



These relationships are shown in Figure 4.

Figure 3. During converter startup, the synchronous MOSFET gate-driver outputs of the SiP11203/SiP11204 are reversed and inverted

to prevent spurious MOSFET switching

Hold-off

MOSFET

Hold-off

MOSFET

SW1 and SW2 are closed at start-up.

SW1

SW2