hcpl0454 Avago Technologies, hcpl0454 Datasheet - Page 19

• Manufacturer Part Number: hcpl0454
• Description: High Cmr, High Speed Optocouplers
• Manufacturer: Avago Technologies

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Data subject to change. Copyright © 2005-2008 Avago Technologies Limited. All rights reserved. Obsoletes AV01-0552EN
AV02-0867EN - June 20, 2008
The LED signal to turn on Q2 should be delayed enough
so that an optocoupler with the very fastest turn-on
propagation delay (t
optocoupler with the very slowest turn-off propagation
delay (t
optocoupler should be delayed by an amount no less
than (t
imum data sheet value for the propagation delay differ-
ence specification, (t
and HCNW4504 specify a maximum (t
over an operating temperature range of 0-70°C.
Although (t
is needed to prevent shoot-through current, it is insuffi-
cient to tell the designer how much dead time a design
will have. Assuming that the optocoupler turn-on delay
is exactly equal to (t
is zero (i.e., there is zero time between the turnoff of the
very slowest optocoupler and the turn-on of the very
fastest optocoupler).
Calculating the maximum dead time is slightly more
complicated. Assuming that the LED turn-on delay is still
exactly equal to (t
that the maximum dead time is the sum of the maximum
difference in turn-on delay plus the maximum difference
in turnoff delay,
[(t
PLHmax
PLHmax
PLHmax
-t
PLHmin
PLH
- t
) turns off. To ensure this, the turn-on of the
-t
PHLmin
)+(t
PHL
PLH
)
PHLmax
max
PLH
), which also happens to be the max-
PLH
PHLmin
- t
tells the designer how much delay
- t
PHL
- t
-t
PHL
PHL
)
PHLmin
max
) will never turn on before an
)
max
). The HCPL-4504/0454/J454
, it can be seen in Figure 17
, the minimum dead time
)].
PLH
- t
PHL
) of 1.3 µs
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This expression can be rearranged to obtain
[(t
and further rearranged to obtain
[(t
which is the maximum minus the minimum data sheet
values of (t
mum and minimum values depends directly on the total
spread in propagation delays and sets the limit on how
good the worst-case dead time can be for a given design.
Therefore, optocouplers with tight propagation delay
specifications (and not just shorter delays or lower pulse-
width distortion) can achieve short dead times in power
inverters. The HCPL-4504/0454/J454 and HCNW4504
specify a minimum (t
ing temperature range of 0-70°C, resulting in a maximum
dead time of 2.0 µs when the LED turn-on delay is equal
to (t
It is important to maintain accurate LED turn-on delays
because delays shorter than (t
shoot-through currents, while longer delays will increase
the worst-case dead time.
PLHmax
PLH
PLH
-t
PHL
-t
-t
PHL
)
PHLmin
max
)
PLH
max
-(t
-t
, or 1.3 µs.
)-(t
PLH
PHL
PHLmin
-t
). The difference between the maxi-
PHL
PLH
)
min
-t
- t
PHLmax
],
PHL
) of -0.7 µs over an operat-
)],
PLH
- t
PHL
)
max
may allow