T. WU, "Cdv/dt induced turn-on in synchronous buck regulators", International Rectifier.

T. WU, "Cdv/dt induced turn-on in synchronous buck regulators", International Rectifier. Copyright - [Précédente] [Première page] [Suivante] - Home

Article : [SHEET209]

Titre : T. WU, Cdv/dt induced turn-on in synchronous buck regulators, International Rectifier.

Cité dans : [DATA211] Recherche d'informations sur les diodes SCHOTTKY, novembre 2000.

Auteur : Thomas Wu - International Rectifier

Stockage : Thierry LEQUEU
Lien : private/Thomas.pdf - 318 Ko, 9 pages.

Abstract :
Cdv/dt induced turn-on of the synchronous MOSFET deteriorates performance in synchronous buck
regulators. We will discuss this problem and provide several solutions that can reduce the effects.

SYNCHRONOUS BUCK REGULATOR

Synchronous buck topology is becoming popular in powering ultra-fast CPU cores. A standard buck
circuit is shown in Figure 1(a) and a synchronous buck is shown in Figure 1(b). As shown in Figure 1(b),
by replacing the freewheeling diode with a MOSFET, the standard buck regulator is converted into a
synchronous buck topology. This topology will provide higher efficiency than the standard buck circuit.
Typically a Schottky diode is paralleled with MOSFET Q2 but is omitted from this paper because it is not
required to understand and solve the Cdv/dt induced turn-on problem.
Ideal synchronous buck regulator waveforms are illustrated in Figure 2(a). The control MOSFET Q1 is
used to regulate the output voltage by adjusting its duty factor. When Q1 is turned off, the inductor current
of Lout continues to flow through either the synchronous MOSFET Q2 or its body diode.

REFERENCES : 4
[1] Robert Martinez and Walid Jarmakani, "Power MOSFET Modeling in Synchronous Buck Regulator", Power 96 Conference, Santa Clara, Oct. 13-16, 1996.
[2] Steve Brown, Sr. "Frequency Dependent Losses & Figure of Merit", International Rectifier internal presentation.
[3] Brian R. Pelly, "The Do’s and Don’ts of Using Power HEXFETtm", International Rectifier Application Note 936A.
[4] IRVRM2 data sheet, International Rectifier.

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