10

Rev. D

04/17/02

HV302 / HV312

Supported External Pass Devices

The HV302 and HV312 are designed to support N-Channel

MOSFETs and IGBTs.

Selection of External Pass Devices

Hotswap action has been completed.

Thus the required

determined from the following equation:

)

MAX

(

LOAD

2

)

ON

(

DS

CONT

I

R

P

×

=

and on the assumption that a output is shorted. The peak power

rating may be calculated from the following equation:

CB

IN

PEAK

I

V

P

×

=

Given these values an external pass transistor may be selected

from the manufacturers data sheet.

Paralleling External Pass Transistors

Due to variations in threshold voltages and transconductance

characteristics between samples of MOSFETs, reliable 50%

current sharing is not achievable. Some measure of paralleling

may be accomplished by adding resistors in series with the source

of each device; however, it will cause increased voltage drop and

power dissipation.

Paralleling of external Pass devices is not recommended!

If a sufficiently high current rated external pass transistor cannot

be found then increased current capability may be achieved by

connecting independent Hotswap circuits in parallel, since they act

as current sources during the load capacitor charging time when

the circuits are in current limit. For this application the HV302 with

active high PWRGD is recommended where the PWRGD pins of

multiple Hotswap circuits can be connected in a wired OR

configuration.

Kelvin Connection to Sense Resistor

Physical layout of the printed circuit board is critical for correct

current sensing. Ideally trace routing between the current sense

as possible with zero current in the sense traces. The use of

ends of the current sense resistor is recommended.

To Negative

Terminal of

Power Source

To Source

of MOSFET

To

VEE

Pin

To

SENSE

Pin

Sense Resistor

Supertex, Inc. 1235 Bordeaux Drive, Sunnyvale, CA 94089 TEL: (408) 744-0100 Fax: (408) 222-4895 www.supertex.com