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Smart gate drives for switched-tank voltage converters

IP.com Disclosure Number: IPCOM000250385D
Publication Date: 2017-Jul-07

Publishing Venue

The IP.com Prior Art Database

Abstract

Voltage-level converters based on switched tank circuits are popular as power-supply

devices for consumer and enterprise equipment. This is due to their high efficiency, high

component density, and low cost, e.g., for high voltage-ratio bus conversion applications. A

hotswap circuit is typically used at the front-end to prevent inrush of current during swapping

or insertion of line-cards into a live backplane ("hotswapping"). Without a protective

mechanism to prevent inrush of current, MOSFETs within the voltage converter get damaged

due to drain-to-source voltages exceeding breakdown specifications. Additionally, voltage

waveforms are turned on in a specific sequence to prevent damage to MOSFETs.

This disclosure describes protective circuits for MOSFETs in voltage-level converters.

The circuits described prevent damage arising from improper sequencing of voltage waveforms

and prevent excessive build-up of drain-to-source voltage. The circuits enable the hotswap

circuit to be eliminated, leading to simple, efficient, and less-costly voltage converters.

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Smart gate drives for switched-tank voltage converters

ABSTRACT

Voltage-level converters based on switched tank circuits are popular as power-supply

devices for consumer and enterprise equipment. This is due to their high efficiency, high

component density, and low cost, e.g., for high voltage-ratio bus conversion applications. A

hotswap circuit is typically used at the front-end to prevent inrush of current during swapping

or insertion of line-cards into a live backplane (“hotswapping”). Without a protective

mechanism to prevent inrush of current, MOSFETs within the voltage converter get damaged

due to drain-to-source voltages exceeding breakdown specifications. Additionally, voltage

waveforms are turned on in a specific sequence to prevent damage to MOSFETs.

This disclosure describes protective circuits for MOSFETs in voltage-level converters.

The circuits described prevent damage arising from improper sequencing of voltage waveforms

and prevent excessive build-up of drain-to-source voltage. The circuits enable the hotswap

circuit to be eliminated, leading to simple, efficient, and less-costly voltage converters.

KEYWORDS

Voltage-level converter; Switched tank converter; Hot swap; E-fuse circuit

BACKGROUND

Fig. 1 shows an example circuit (100) for a voltage-level converter based on a switched-

tank topology. Input voltage at a certain level Vin (102) is converted to output level Vout (104)

by circuit 100. The voltage converter 100 includes a “high side” (or wing side) (106),

comprising capacitors, inductors, MOSFETs, gate-driver circuits, etc., as it typically connects

to an input voltage Vin that is higher than the output voltage Vout. Wing side (106) comprises

several nearly identical stages. Each stage includes paired MOSFETs (110). The voltage

converter also includes a “low side” (108) that comprises components including capacitors,

inductors, MOSFETs, gate-driver circuits, etc. that are connected to the output voltage Vout.

High-efficiency operation of the voltage converter is made possible by use of MOSFETs

(110) with high figure-of-merit (FoM). A high figure-of-merit MOSFET requires a low amount

of charge to turn ON and has a low resistance during the ON state. A high FoM MOSFET

needs to be guarded against excessive drain-to-source voltage, since high drain-to-source

voltage causes breakdown. A hotswap or e-fuse circuit (112) is typically used to prevent

excessive build-up of drain-to-source voltage across high FoM MOSFETs (110).

The voltage-conversion ratio is based on the duty cycle of a pulse-wave modulated

(PWM) waveform that feeds into the gates of MOSFETs in the wing side and the low side.

Circuit 100 includes circuitry (116) that generates the PWM, with a PWM control circuit (114).

To prevent malfunction or breakdown of MOSFETs, the PWM is turned on prior to enabling

the hotswap circuit, and input voltage Vin is activated thereafter. If the sequence of waveform

activation, e.g., PWM before hotswap before Vin, is not followed,...