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Data subject to change. Copyright © 2005-2008 Avago Technologies Limited. All rights reserved. Obsoletes AV01-0551EN

AV02-1360EN - June 20, 2008

IPM Dead Time and Propagation Delay Specifications

The HCPL-4506 series include a Propagation Delay Differ-

ence specification intended to help designers minimize

“dead time” in their power inverter designs. Dead time is

the time period during which both the high and low side

power transistors (Q1 and Q2 in Figure 24) are off. Any

overlap in Q1 and Q2 conduction will result in large cur-

rents flowing through the power devices between the

high and low voltage motor rails.

To minimize dead time the designer must consider the

propagation delay characteristics of the optocoupler

as well as the characteristics of the IPM IGBT gate drive

circuit. Considering only the delay characteristics of the

optocoupler (the characteristics of the IPM IGBT gate

drive circuit can be analyzed in the same way) it is impor-

erably over the desired operating temperature range.

The limiting case of zero dead time occurs when the in-

put to Q1 turns off at the same time that the input to

Q2 turns on. This case determines the minimum de-

lay between LED1 turn-off and LED2 turn-on, which

is related to the worst case optocoupler propagation

delay waveforms, as shown in Figure 25. A minimum

dead time of zero is achieved in Figure 25 when the

delays used to calculate PDD are taken at equal tem-

peratures since the optocouplers under consideration

are typically mounted in close proximity to each other.

full operating temperature range, specified in the data

sheet.) This delay is the maximum value for the propaga-

tion delay difference specification which is specified at

450 ns for the HCPL-4506 series over an operating tem-

perature range of -40°C to 100°C.

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 maxi-

mum dead time will be. The maximum dead time oc-

curs in the highly unlikely case where one optocoupler

are in the same inverter leg. The maximum dead

time in this case becomes the sum of the spread

The maximum dead time is also equivalent to the differ-

ence between the maximum and minimum propagation

delay difference specifications. The maximum dead time

(due to the optocouplers) for the HCPL-4506 series is

600 ns (= 450ns - (-150 ns) ) over an operating tempera-

ture range of -40°C to 100°C.