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VLA503

Hybrid IC GBT Gate Driver

Powerex 

Powerex, Inc., 173 Pavilion Lane, Youngwood, Pennsylvania 15697-1800 (724) 925-7272

VLA503

Hybrid IC IGBT Gate Driver

General Description

The VLA503 is a hybrid integrated circuit designed

to provide gate drive for high power IGBT modules.

This circuit has been optimized for use with Powerex

NF-Series and A-Series IGBT modules. However,

the output characteristics are compatible with most

MOS gated power devices. The VLA503 features a

compact single-in-line package design. The upright

mounting minimizes required printed circuit board space

to allow efficient and flexible layout. The VLA503

converts logic level control signals into fully isolated

+15V/-8V gate drive with up to 5A of peak drive current.

Control signal isolation is provided by an integrated high

speed opto-coupler. Short circuit protection is provided

by means of destauration detection.

Short Circuit Protection

Figure 1 shows a block diagram of a typical desatura-

tion detector. In this circuit, a high voltage fast recovery

diode (D1) is connected to the IGBT’s collector to moni-

tor the collector to emitter voltage. When the IGBT is

in the off state, VCE is high and D1 is reverse biased.

With D1 off the (+) input of the comparator is pulled up

to the positive gate drive power supply (V+) which is

normally +15V. When the IGBT turns on, the compara-

tors (+) input is pulled down by D1 to the IGBT’s VCE(sat).

The (-) input of the comparator is supplied with a fixed

voltage (VTRIP). During a normal on-state condition

the comparator’s (+) input will be less than VTRIP and

it’s output will be low. During a normal off-state condi-

tion the comparator’s (+) input will be larger than VTRIP

V+

INPUT

D1

+

DELAY

ttrip

COMPARE

Vtrip

AND

C

SHUTDOWN

GATE

DRIVE

RG

G

IGBT

MODULE

E

E

Figure 1. Desaturation Detector

and it’s output will be high. If the IGBT turns on into a

short circuit, the high current will cause the IGBT’s col-

lector-emitter voltage to rise above VTRIP even though

the gate of the IGBT is being driven on. This abnormal

presence of high VCE when the IGBT is supposed to

be on is often called desaturation. Desaturation can

be detected by a logical AND of the driver’s input signal

and the comparator output. When the output of the AND

goes high a short circuit is indicated. The output of the

AND can be used to command the IGBT to shut down in

order to protect it from the short circuit. A delay (tTRIP)

must be provided after the comparator output to allow

for the normal turn on time of the IGBT. The tTRIP delay

is set so that the IGBTs VCE has enough time to fall

below VTRIP during normal turn on switching. If tTRIP

is set too short, erroneous desaturation detection will

occur. The maximum allowable tTRIP delay is limited by

the IGBT’s short circuit withstanding capability. In typical

applications using Powerex IGBT modules the recom-

mended limit is 10µs.

Operation of the VLA503 Desaturation Detector

The Powerex VLA503 incorporates short circuit pro-

tection using desaturation detection as described

above. A flow chart for the logical operation of the

short-circuit protection is shown in Figure 2. When a

desaturation is detected the hybrid gate driver performs

a soft shut down of the IGBT and starts a timed (ttimer)

1.5ms lock out. The soft turn-off helps to limit the tran-

sient voltage that may be generated while interrupting

the large short circuit current flowing in the IGBT. During

the lock out the driver pulls Pin 8 low to indicate the fault

status. Normal operation of the driver will resume after

the lock-out time has expired and the control input signal

returns to its off state.

Adjustment of Trip Time

The VLA503 has a default short-circuit detection

time delay (tTRIP) of approximately 2.5µs. This will

prevent erroneous detection of short-circuit conditions

as long as the series gate resistance (RG) is near the

minimum recommended value for the module being

used. The 2.5µs delay is appropriate for most applica-

tions so adjustment will not be necessary. However, in

some low frequency applications it may be desirable to

use a larger series gate resistor to slow the switching of

the IGBT, reduce noise, and limit turn-off transient volt-

ages. When RG is increased, the switching delay time

of the IGBT will also increase. If the delay becomes

Rev. 2/06

5

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