ACPL-38JT-000E Datasheet, PDF (33/33 Pages) AVAGO TECHNOLOGIES LIMITED – Automotive Gate Drive Optocoupler with R2Coupler™ Isolation, 2.5 Amp Output Current, Integrated Desaturation (VCE) Detection and Fault Status Feedback

System Considerations
Propagation Delay Difference (PDD)
The ACPL-38JT includes a Propagation Delay Difference
(PDD) 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 62) are off.
Any overlap in Q1 and Q2 conduction will result in large
currents flowing through the power devices between
the high and low voltage motor rails, a potentially cata-
strophic condition that must be prevented.
To minimize dead time in a given design, the turn-on of
the ACPL-38JT driving Q2 should be delayed (relative to
the turn-off of the ACPL-38JT driving Q1) so that under
worst-case conditions, transistor Q1 has just turned off
when transistor Q2 turns on, as shown in Figure 80. The
amount of delay necessary to achieve this condition is
equal to the maximum value of the propagation delay
difference specification, P_DDMAX, which is specified to be
400 ns over the operating temperature range of -40°C to
125°C.
Delaying the ACPL-38JT turn-on signals 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 specifications
as shown in Figure 79. The maximum dead time for the
ACPL-38JT is 800 ns (= 400 ns - (-400 ns)) over an operating
temperature range of -40°C to 125°C.
Note that the propagation delays used to calculate PDD
and dead time are taken at equal temperatures and test
conditions since the components under consideration are
typically mounted in close proximity to each other and are
switching identical IGBTs.
ILED1
VOUT1
VOUT2
Q1 ON
Q2 OFF
Q1 OFF
Q2 ON
ILED2
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.
Figure 78. Minimum LED Skew for Zero Dead Time.
ILED1
VOUT1
Q1 ON
Q1 OFF
VOUT2
Q2 OFF
Q2 ON
ILED2
tPLH MIN
tPHL MAX
tPLH MIN
(tPHL - tPLH) MAX
PDD* MAX
tPLH MAX
MAXIMUM DEAD TIME
(DUE TO OPTOCOUPLER)
= (t_{PHL MAX} - t_{PHL MIN}) + (t_{PLH MAX} - t_{PLH MIN})
= (t_{PHL MAX} - t_{PLH MIN}) + (t_{PHL MIN} - t_{PLH 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.
Figure 79. Waveforms for Dead Time Calculation.
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Data subject to change. Copyright © 2005-2012 Avago Technologies. All rights reserved.
AV02-2546EN - February 17, 2012