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VLA502-01

Hybrid IC IGBT Gate Driver + DC/DC Converter

Powerex 

Powerex, Inc., 200 E. Hillis Street, Youngwood, Pennsylvania 15697-1800 (724) 925-7272

VLA502-01

Hybrid IC IGBT Gate Driver +

DC/DC Converter

General Description

The VLA502-01 is a hybrid integrated circuit designed to

provide gate drive for high power IGBT modules. This

circuit has been optimized for use with Powerex NFH-

Series IGBT modules. However, the output char-

acteristics are compatible with most MOS gated

power devices. The VLA502-01 features a compact

single-in-line package design. The upright mount-

ing design minimizes printed circuit board space to

allow efficient and flexible layout. The VLA502-01

converts logic level control signals into fully isolated

+15V/-8V gate drive with up to12A of peak drive current.

Isolated drive power is provided by a built in DC-to-DC

converter and control signal isolation is provided by an

integrated high speed opto-coupler. Short circuit protec-

tion 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 nor-

mally +15V. When the IGBT turns on, the comparators

(+) 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 out-

put will be low. During a normal off-state condition the

comparator’s (+) input will be larger than Vtrip and it’s out-

put will be high. If the IGBT turns on into a short circuit,

the high current will cause the IGBT’s collector-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 com-

parator 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 nor-

mal turn on time of the IGBT. The ttrip delay is set so

that the IGBT's 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 maxi-

mum allowable ttrip delay is limited by the IGBT’s short

circuit withstanding capability. In typical applications

using Powerex IGBT modules the recommended limit is

10us.

Operation of the VLA502-01 Desaturation Detector

The Powerex VLA502-01 incorporates short circuit

protection 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 desatura-

tion is detected the hybrid gate driver performs a soft

shutdown of the IGBT and starts a timed (ttimer) 1.5ms

lock out. The soft turn-off helps to limit the transient

voltage that may be generated while interrupting the

large short circuit current flowing in the IGBT. During the

lock out the driver pulls Pin 28 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 VLA502-01 has a default short-circuit detection

time delay (ttrip) of approximately 3µs. This will prevent

erroneous detection of short-circuit conditions as long

as the series gate resistance (RG) is near the mini-

mum recommended value for the module being used.

The 3µs delay is appropriate for most applications 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

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Figure 1. Desaturation Detector

6

Rev. 8/06

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