ACPL-P302 datasheet(13/15 Pages) BOARDCOM

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Broadcom Confidential

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ACPL-P302/ACPL-W302

Data Sheet

Dead Time and Propagation Delay

Specifications

The ACPL-P302/W302 includes a Propagation Delay Differ-

ence (PDD) specification intended to help designers mini-

mize “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, tran-

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

shown in Figure 24. The amount of delay necessary to achieve

this condition is equal to the maximum value of the propaga-

tion delay difference specification, PDD max, which is specified

to be 500 ns over the operating temperature range of -40° to

100°C.

Figure 24 Minimum LED Skew for Zero Dead Time

Figure 25 Waveforms for Dead Time

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 25. The maximum

dead time for the ACPL-P302/W302 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 condi-

tions since the optocouplers under consideration are typically

mounted in close proximity to each other and are switching

identical IGBTs.

tPHL MAX

tPLH MIN

PDD* MAX = (tPHL- tPLH)MAX = tPHL MAX - tPLH MIN

*PDD = PROPAGATION DELAY DIFFERENCE

NOTE: FOR PDD CALCULATIONS THE PROPAGATION DELAYS

ARE TAKEN AT THE SAME TEMPERATURE AND TEST CONDITIONS.

VOUT1

ILED2

VOUT2

ILED1

Q1 ON

Q2 OFF

Q1 OFF

Q2 ON

tPLH

MIN

MAXIMUM DEAD TIME

(DUE TO OPTOCOUPLER)

= (tPHL MAX - tPHL MIN) + (tPLH MAX - tPLH MIN)

= (tPHL MAX - tPLH MIN) – (tPHL MIN - tPLH MAX)

= PDD* MAX – PDD* MIN

*PDD = PROPAGATION DELAY DIFFERENCE

NOTE: FOR DEAD TIME AND PDD CALCULATIONS ALL PROPAGATION

DELAYS ARE TAKEN AT THE SAME TEMPERATURE AND TEST CONDITIONS.

VOUT1

ILED2

VOUT2

ILED1

Q1 ON

Q2 OFF

Q1 OFF

Q2 ON

tPHL MIN

tPHL MAX

tPLH MAX

PDD* MAX

(tPHL-tPLH) MAX

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