SN74LVC1G123: Pulse Length Detection

Kazuki Itoh

Part Number: SN74LVC1G123
Other Parts Discussed in Thread: SN74HCS72

Hi team,

My customer is considering the circuit which turns off LED driving FET if the FET gate pulse lengh is longer than specific length (a couple of mill seconds).

Is SN74LVC1G123 right device to do that?

How should my customer configure the circuit with SN74LVC1G123?

Regards,

Itoh

over 5 years ago

0 Clemens Ladisch over 5 years ago

Guru 317370 points

When the input is connected to B, the output pulse will always have the same length, even when the gate pulse is shorter:

When the input is connected to CLR, the output will be interrupted when the input goes low again.

See Designing with the SN74LVC1G123 Monostable Multivibrator.

0 Kazuki Itoh over 5 years ago in reply to Clemens Ladisch

TI__Genius 10840 points

Hi Clemens-san,

My customer wants to assert output when the input pulse is longer than specific pulse length.

Does SN74LVC1G123 can do the thing like that?

Hope it makes sense.

Regards,

Itoh

0 Clemens Ladisch over 5 years ago in reply to Kazuki Itoh

Guru 317370 points

Something like this?

Should the output signal be high or low? Should it be latched?

0 Emrys Maier over 5 years ago

TI__Guru* 97046 points

Hi Itoh-san,

The SN74LVC1G123 can produce a pulse of a given length, but does not detect the length of an input pulse.

One way to do this would be to trigger the SN74LVC1G123 with the input pulse, and feed the output pulse of the '123 to a negative edge triggered D-type flip flop (ex: SN74HCS72).

If the input to the DFF is the input signal, and the clock signal is from the '123, then the output will be LOW if the input is shorter than the '123 pulse width, and HIGH if the input is longer than the '123 pulse width.

You can reverse the output states by just using the inverted output (Q\) instead of the normal output (Q).

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SN74LVC1G123: Pulse Length Detection