CD74HC123: Is it ok to leave Rext/Cext pin open and to connect Cext pin to GND when one of multivibrators in CD74HC123 is unused?

Kazuya Nakai59

Guru 20620 points

Part Number: CD74HC123
Other Parts Discussed in Thread: SN74LVC1G123

Hello guys,

One of my customers is going to use CD74HC123 for their new products.

Also they need just one multivibrator. So they don't need one of two multivibrator in the device.

They want to know how to terminate Cext and Rext/Cext pin of unused multivibrator.

they think the followings are correct.

Cext=GND, Rext/Cext=open

Is their understanding correct?

Could you please tell me your reply?

Best regards,

Kazuya.

over 3 years ago

0 Clemens Ladisch over 3 years ago

Guru 267740 points

The Cx pin is internally grounded. And when the RxCx pin is open, it might float near the switching threshold. You should just short these two pins (i.e., C = 0, R = ∞). But it's probably not important as long as this multivibrator is not actually triggered.

Why not use a single-channel device like the SN74LVC1G123?

0 Kazuya Nakai59 over 3 years ago in reply to Clemens Ladisch

Guru 20620 points

Hello Clemens,

Thank you for your reply.

It is helpful for the customer.

They know 1G logic family but they want to use CD74HC123 because the device has been used for many of their current products.

Thank you again and best regards,

Kazuya.

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CD74HC123: Is it ok to leave Rext/Cext pin open and to connect Cext pin to GND when one of multivibrators in CD74HC123 is unused?