13
Dead Time and Propagation Delay Specications
The ACPL-P302/W302 includes a Propagation Delay Dif-
ference (PDD) specication intended to help designers
minimize “dead time” in their power inverter designs.
Dead time is the time high and low side power transistors
are o. Any overlap in Ql and Q2 conduction will result in
large currents owing through the power devices from
the high voltage to the low-voltage motor rails. To mini-
mize dead time in a given design, the turn on of LED2
should be delayed (relative to the turn o of LED1) so that
under worst-case conditions, transistor Q1 has just turned
o 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 propagation delay
dierence specication, PDD max, which is specied 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 dierence 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 dierence between the maximum and minimum
propagation delay dierence specication 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 tem-
perature 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.
t
PHL MAX
t
PLH MIN
PDD* MAX = (t
PHL
-
t
PLH
)
MAX
= t
PHL MAX
-
t
PLH MIN
*PDD = PROPAGATION DELAY DIFFERENCE
NOTE: FOR PDD CALCULATIONS THE PROPAGATION DELAYS
ARE TAKEN AT THE SAME TEMPERATURE AND TEST CONDITIONS.
V
OUT1
I
LED2
V
OUT2
I
LED1
Q1 ON
Q2 OFF
Q1 OFF
Q2 ON
t
PLH
MIN
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.
V
OUT1
I
LED2
V
OUT2
I
LED1
Q1 ON
Q2 OFF
Q1 OFF
Q2 ON
t
PHL MIN
t
PHL MAX
t
PLH MAX
PDD* MAX
(t
PHL-
t
PLH
)
MAX
