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Data subject to change. Copyright © 2006 Avago Technologies, Limited. All rights reserved. Obsoletes AV01-0278EN

AV01-0634EN - Nopvember 8, 2006

Dead Time and Propagation Delay Specifications

The ACPL-P314/W314 includes a Propagation Delay

Difference (PDD) specification intended to help

designers minimize “dead time” in their power inverter

designs. Dead time is the time high and low side power

transistors are off. Any overlap in Ql and Q2 conduction

will result in large currents flowing through the power

devices from the high voltage to the low-voltage motor

rails. To minimize dead time in a given design, the turn

on of LED2 should be delayed (relative to the turn off

of LED1) so that under worst-case conditions, transistor

Q1 has just turned off when transistor Q2 turns on, as

shown in Figure 26. The amount of delay necessary to

achieve this condition is equal to the maximum value

of the propagation delay difference specification, PDD

max, which is specified to be 500 ns over the operating

temperature range of -40° to 100°C.

Figure 26. Minimum LED Skew for Zero Dead Time.

Figure 27. Waveforms for Dead Time.

Figure 25. Recommended LED Drive Circuit for Ultra-High CMR

Dead Time and Propagation Delay Specifications.

C

LEDP

C

LEDN

6

1

5

2

4

3

SHIELD

+5 V

C

LEDP

C

LEDN

6

1

5

2

4

3

+5 V

Delaying the LED signal by the maximum propagation

delay difference ensures that the minimum dead time

is zero, but it does not tell a designer what the

maximum dead time will be. The maximum dead time

is equivalent to the difference between the maximum

and

minimum

propagation

delay

difference

specification as shown in Figure 27. The maximum

dead time for the ACPL-P314/W314 is 1 µs (= 0.5 µs - (-

0.5 µs)) over the operating temperature range of –40°C

to 100°C.

Note that the propagation delays used to calculate PDD

and dead time are taken at equal temperatures and

test conditions since the optocouplers under

consideration are typically mounted in close proximity

to each other and are switching identical IGBTs.