Anti-Cross Conduction to Prevent Current Shoot Through and Determining Dead Time
The ACPL-H342 includes a Propagation Delay Difference (PDD = tPHL – tPLH ) specification to help prevent both the
high(Q1) and low(Q2) side power transistors from turning on at the same time. This “Anti-Cross” conduction feature
prevents large currents from flowing through the power transistors by ensuring tPHLMAX is faster than tPLHMIN. In another
words, the “Anti-Cross” feature will ensure one power transistor is turned off before the other is turned on.
A gate driver without Anti-Cross feature will for example has a PDDMIN of -350ns and a PDDMAX of 350ns. A positive
PDDMAX of 350ns would mean one transistor will be turn on before the other is off since tPHLMAX is longer than tPLHMIN.
This is shown in Figure 37. To prevent this and the shoot through current, the turn on of LED2 should be delayed (relative
to the turn off of LED1) so that under worst-case conditions, Q1 has just turned off when Q2 turns on. The amount of
delay to achieve this condition is equal to PDDMAX as shown in Figure 38.
R
High Side PWM
+ HVDC
RG
Low Side PWM
LED1
R
VOUT1
Q1
AC
RG
LED2
VOUT2
Q2
-HVDC
ILED1
VOUT1
Q1 ON
tPHLMAX
VOUT2 Q2 OFF tPLHMIN
Q2 ON
Q1 OFF
ILED2
Shoot
Through
Figure 37. Current shoot through without Anti-Cross feature
ILED1
VOUT1
VOUT2
Q1 ON
tPHLMAX
Q2 OFF
Q1 OFF
Q2 ON
ILED2
tPLHMIN
PDDMAX = tPHLMAX - tPLHMIN = 350 ns
Figure 38. Adding delay to prevent shoot through
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