Philips Semiconductors

PIP202-12M-2

DC-to-DC converter powertrain

Product data

Rev. 02 — 24 November 2003

4 of 20

9397 750 11943

© Koninklijke Philips Electronics N.V. 2003. All rights reserved.

When the input voltage is LOW and current is flowing in the inductor, the upper

MOSFET must be off and the lower MOSFET must be on. Current flows from the

output.

Finally, when switching between states, both MOSFETs must not be on at the same

time.

7.2 MOSFET driver function

The input, output and gate drive waveforms are shown in Figure 4. When the input

voltage goes HIGH, the gate drive to the lower MOSFET immediately goes LOW. This

causes the output current to flow through the Schottky diode, connected between the

drain and source of the lower MOSFET. This causes output voltage to fall from zero to

approximately

−0.5 V.

After a delay, if the input voltage is still HIGH, the gate drive to the upper MOSFET

goes HIGH. This causes the output voltage to rise to the output stage supply voltage,

When the input voltage goes LOW, the gate drive to the upper MOSFET immediately

diode at approximately

−0.5 V.

After a delay, if the input voltage is still LOW, the gate drive to the lower MOSFET

goes HIGH. The lower MOSFET turns on, and the output voltage rises from

−0.5 V to

zero.

7.3 Bootstrap diode

CB.

Fig 4.

Input, output and gate drive waveforms of a synchronous DC-to-DC converter

output stage.

input voltage

output voltage

upper MOSFET

gate drive

lower MOSFET

gate drive

03ag35

delay

delay