SN74LVC8T245: Pull ups at output

Akash S

Part Number: SN74LVC8T245
Other Parts Discussed in Thread: SN74LXC8T245

Hi,

Can I have pull up resistors at the output of the level translator, so that the output is at a defined state when the input is floating

over 3 years ago

0 Clemens Ladisch over 3 years ago

Guru 317260 points

When an input is floating, it is read as high, or low, or it might oscillate. An enabled output never floats.

Place the pull-up at the input.

0 Akash S over 3 years ago

Intellectual 790 points

Thanks Clemens for the reply.

Is it okay if there are pull ups on both sides i.e., input and output

0 Clemens Ladisch over 3 years ago in reply to Akash S

Guru 317260 points

Yes, this is OK. (The pull-up at the output will have an effect only when the device is powered off or disabled.)

0 Karan Kotadia over 3 years ago in reply to Clemens Ladisch

TI__Genius 16735 points

Hi Akash,

Can I also suggest the SN74LXC8T245? It has built in dynamic pull-downs if you are worried about floating inputs while switching direction.

The dynamic pull-downs will only activate if the device is disabled in someway and then hold the input low. If you are going to have floating inputs during operation then you will need external pull-ups or pull-downs.

Regards,

Karan

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SN74LVC8T245: Pull ups at output