AM26LS32AC: The fail-safe does not work on some of my boards.

Charles Kaseff

Part Number: AM26LS32AC
Other Parts Discussed in Thread: SN65LBC173A, AM26LV32, SN75LBC173A

I am using an AM26LS32ACPWR. There is a 100-ohm termination resistor between the A and B inputs. When these inputs are floating, I expect to see a high on the Y output due to the fail-safe function in this device. However, on some of the boards, the Y output is low. Is there something I can do besides adding pullup/pulldown resistors on the A and B inputs?

over 2 years ago

0 Clemens Ladisch over 2 years ago

Guru 322010 points

The datasheet says:

Fail-safe design ensures that, if the inputs are open, the outputs always are high.

If the inputs are connected with the termination resistor, they are not open.

You need receivers that have not only open-circuit fail-safe, but also short-circuit and terminated fail-safe, such as the AM26LV32 (but not the AM26‍LV32E) or the SN65LBC173A/SN75LBC173A.

+1 Eric Hackett over 2 years ago in reply to Clemens Ladisch

TI__Guru 74372 points

Thanks for the help Clemens!

Charles,

Please let us know if you have any other questions.

Regards,

Eric Hackett

Interface

Interface forum

AM26LS32AC: The fail-safe does not work on some of my boards.