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momentary current peaks to the
LED during the turn-on and turn-
off transitions of the drive
current. These peak currents help
to charge and discharge the
capacitances of the LED more
quickly, shortening the time
required for the LED to turn on
and off.
Switching performance of the
HCPL-2400/30 optocouplers is
not sensitive to the TTL logic
family used in the recommended
drive circuit. The typical and
worst-case switching parameters
given in the data sheet can be met
using common 74LS TTL invert-
ing gates or buffers. Use of faster
TTL families will slightly reduce
the overall propagation delays
from the input of the drive circuit
to the output of the optocoupler,
but will not necessarily result in
lower pulse-width distortion or
propagation delay skew. This
reduction in overall propagation
delay is due to shorter delays in
the drive circuit, not to changes in
the propagation delays of the
optocoupler; optocoupler prop-
agation delays are not affected by
the speed of the logic used in the
drive circuit.
