AN1135| Application Note
Maxim/Dallas > App Notes > POWER-SUPPLY CIRCUITS Keywords: Small Capacitor Improves Efficiency in High-Power CPU Supply
Jun 27, 2002
APPLICATION NOTE 1135
Small Capacitor Improves Efficiency in High-Power CPU Supply
For the high-VIN DC/DC buck converters that supply high current in notebook PCs, high efficiency is very important for the purpose of extending battery life and minimizing temperature rise. A low-dissipation synchronous rectifier with external MOSFET also supports this purpose. Synchronous rectifiers require special attention, however. Bad designs allow shoot-through current when the high-side and low-side MOSFETs are on simultaneously. Some engineers believe enough dead time (between turn-off of one MOSFET and turn-on of the other) can eliminate this problem, but dead time is not sufficient in some applications. Figure 1 illustrates a stepdown power supply in which a stepdown controller (MAX1718) provides the CPU-core supply. Recent CPU cores require a very low supply rail (1V to 2V) with more than 20A of current. The input voltage range, on the other hand, is high (7V to 20V). These circumstances force a very low duty cycle for the high-side MOSFET (Q1).
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