AN-6003

www.DataSheet4U.com www.fairchildsemi.com AN-6003 “Shoot-through” in Synchronous Buck Converters Jon Klein Power Management Applications Abstract The synchronous buck circuit is in widespread use to provide “point of use” high current, low voltage power for CPU’s, chipsets, peripherals etc. In the synchronous buck converter, the power stage has a “high-side” (Q1 below) MOSFET to charge the inductor, and a “Low-side” MOSFET which replaces a conventional buck regulator’s “catch diode” to provide a low-loss recirculation path for the inductor current. V IN PWM CONTROLLER 2. Adaptive gate drive: This circuit looks at the VGS of the MOSFET that’s being driven off to determine when to turn on the complementary MOSFET. Theoretically, adaptive gate drives produce the shortest possible dead-time for a given MOSFET without producing shootthrough. H igh-S ide Q1 VO U T L1 In practice, a combination of adaptive and fixed produces the best results, and is typically what is in today’s PWM controllers and gate drivers as shown in Figure 2 D1 BOOT RG V IN +5 C BO O T + – D C GD PW M 1V + D elay SW H D RV R G A TE G C GS S D C GD LDR V PW M R G A TE G C GS S D elay + 1V PG ND Low -S ide Q2 Figure 1. Synchronous Buck output stage Q1 Shoot-through is defined as the condition when both MOSFETs are either fully or partially turned on, providing a path for current to “shoot through” from VIN to GND. To minimize shoot-through, synchronous buck regulator IC’s employ one of two technique...