CDCLVP1208: Unused input to create an "output enable" pin

Zach Kimble

Intellectual 1940 points

Part Number: CDCLVP1208

Hello,

I am interested in using the CDCLVP1208 but my design requires an output enable pin. Since I only have one input, I was thinking I could connect my input clock signal to IN1 and leave IN0 floating. I would put a pulldown resistor on IN_SEL so the input mux defaults to IN0. Then, IN_SEL would effectively work as an active high output enable pin because if I put a 1 on IN_SEL, it will connect IN1 to the outputs. When IN_SEL is driven to 0, there would be no output from the device.

Would the setup I described work to effectively give me an output enable pin for this device? Do you foresee any issues with this setup?

Thank you!

Best regards,

Zach Kimble

over 2 years ago

0 Connor Lewis over 2 years ago

TI__Genius 12770 points

Hi Zach,

Yes, that setup could work to add output enable functionality. I would actually recommend pulling down IN0 instead of leaving it floating to make sure the output stays in a well-defined low/low state. This would also help prevent noise from coupling to the inputs of the buffer.

Regards,

Connor

0 Zach Kimble over 2 years ago in reply to Connor Lewis

TI__Intellectual 1940 points

Hi Connor,

Thank you!

In the datasheet it mentions that unused input pairs can be left floating. Just to confirm, it is okay to have them pulled down to ground with nothing else connected? Just a resistor to ground connected to each pin? Would 1k be a good size for the resistor?

Best regards,

Zach Kimble

+1 Connor Lewis over 2 years ago in reply to Zach Kimble

TI__Genius 12770 points

Hi Zach,

I believe when the datasheet mentions that an input can be left floating, that's under the assumption that it will never be selected as the active input. Most likely it would be fine to leave them floating in most situations, but I think in this case it would be best practice to pull it down if it's being selected just to keep the device behavior as predictable as possible. I think just a simple 1K resistor to ground on each pin should work fine, let me know if you run into any issues.

Regards,

Connor

0 Zach Kimble over 2 years ago in reply to Connor Lewis

TI__Intellectual 1940 points

Hi Connor,

Thank you very much for confirming! I will go ahead and try this out and let you know if there are any issues.

Best regards,

Zach Kimble

Clock & timing

Clock & timing forum

CDCLVP1208: Unused input to create an "output enable" pin