Browse Prior Art Database

HIGH SIDE DRIVER FET LOAD-DUMP PROTECTION

IP.com Disclosure Number: IPCOM000005798D
Original Publication Date: 1989-Aug-01
Included in the Prior Art Database: 2001-Nov-07
Document File: 2 page(s) / 72K

Publishing Venue

Motorola

Related People

John Qualich: AUTHOR

Abstract

It is desirable to turn a high-side drive automotive FET switch 'on'during overvoltage transients such as load dump in order to protect the FET This prevents the FET from exceeding its rated drain to source voltage. To limit device power dissipation, it is desirable to not just clamp V,, but to turn the FET on so that the load dump energy is dissipated in the load. In an application such as Figure 1 with no explicit ground pin, it is dif- ficult to detect a load dump when switch Sl is open.

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MOlOROLA Technical Developments Volume 9 August 1989

HIGH SIDE DRIVER FET LOAD-DUMP PROTECTION

by John Qualich

   It is desirable to turn a high-side drive automotive FET switch 'on'during overvoltage transients such as load dump in order to protect the FET This prevents the FET from exceeding its rated drain to source voltage. To limit device power dissipation, it is desirable to not just clamp V,, but to turn the FET on so that the load dump energy is dissipated in the load. In an application such as Figure 1 with no explicit ground pin, it is dif- ficult to detect a load dump when switch Sl is open.

"BATT , P-

POS.1

I I I

NOTE: THE SWITCHING MODULE IS DESIGNED SUCH THAT IF St

IS CLOSED, THE FET WILL CONDUCT CURRENT.

TI

I I

"BATTo-]

INPUT

,~~~is,~-,cd~iItiiON, , .~.. , ,y _. ,

P I II

b-iiik&Ti

LOAD

FIG.1

A solution to this problem is to use the load as a low voltage reference during a load dump transient (figure
2). Diodes Dl and D2 select the lowest voltage of the negative input and the load as the module reference voltage. If Sl is closed, the reference will be near ground. If Sl is open, the reference will be nearthe FET source voltage.

   If switch Sl is closed, the FET simply remains on during the load dump. If Sl is open, the zener diode 21 triggers a one-shot oscillator upon load dump. The one-shot will signal the charge pump through the OR gate to turn the FET on for a duration which exceeds the load dump duration. The charge pump is a voltage doubler cir...