System Considerations
Propagation Delay Difference
(PDD)
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 maxi-
mum value of the propagation
delay difference specification,
time is equivalent to the
difference between the maximum
and minimum propagation delay
difference specifications as
shown in Figure 81. The
maximum dead time for the
HCPL-316J is 800 ns (= 400 ns -
(-400 ns)) over an operating
temperature range of -40°C to
100°C.
The HCPL-316J 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
PDD
, which is specified to be
MAX
400 ns 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 tempera-
tures and test conditions since
the optocouplers under consider-
ation are typically mounted in
close proximity to each other and
are switching identical IGBTs.
transistors (Q1 and Q2 in
Delaying the HCPL-316J turn-on
signals by the maximum
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 catastrophic condi-
tion that must be prevented.
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
To minimize dead time in a given
design, the turn-on of the
V
IN+1
HCPL-316J driving Q2 should be
delayed (relative to the turn-off of
the HCPL-316J driving Q1) so
that under worst-case conditions,
V
OUT1
Q1 ON
Q1 OFF
Q2 ON
Q2 OFF
V
OUT2
V
IN+1
V
IN+2
t
PHL
MIN
t
PHL
V
OUT1
Q1 ON
MAX
Q1 OFF
Q2 ON
t
PLH
MIN
t
PLH
MAX
= PDD*
MAX
MAX
Q2 OFF
(t
t
ꢀ
PHL- PLH
V
OUT2
V
IN+2
MAXIMUM DEAD TIME
(DUE TO OPTOCOUPLERꢀ
t
PHL
MAX
= (t
= (t
= PDD*
- t
- t
– PDD*
ꢀ + (t
- t
PLH
ꢀ
MIN
t
PHL
PHL
PHL
PLH
PLH
PLH
MAX
MAX
MAX
MIN
MIN
MAX
MIN
- t
ꢀ – (t
- t
ꢀ
PLH
MAX
PHL
MIN
PDD* MAX = (t
ꢀ
= t
- t
PLH
MAX MIN
PHL PLH
PHL
MAX
MIN
*PDD = PROPAGATION DELAY
NOTE: FOR PDD CALCULATIONS THE PROPAGATION DELAYS
ARE TAKEN AT THE SAME TEMPERATURE AND TEST CONDITIONS.
*PDD = PROPAGATION DELAY DIFFERENCE
NOTE: FOR DEAD TIME AND PDD CALCULATIONS ALL PROPAGATION
DELAYS ARE TAKEN AT THE SAME TEMPERATURE AND TEST CONDITIONS.
Figure 80. Minimum LED Skew for Zero Dead Time.
Figure 81. Waveforms for Dead Time Calculation.
For product information and a complete list of
Agilent contacts and distributors, please go to
our web site.
www.agilent.com/semiconductors
E-mail: SemiconductorSupport@agilent.com
Data subject to change.
Copyright © 2005 Agilent Technologies, Inc.
Obsoletes 5989-0784EN
March 1, 2005
5989-2143EN
AGILENT [ AGILENT TECHNOLOGIES, LTD. ]
