SN75C1167: Customer test the chip with UART signal, please help to confirm the behavior would be normal or not?

George Liu1

Part Number: SN75C1167

Hi Sir,

Customer used the SN75C1167 for the UART signal design, now they have made a testing method but they encountered a behavior but not sure it is abnormal or not.

They simple test the chip only, without any pcb and not connect the Vcc. Then input the UART signal on pin 15 (D) or pin 3 (R)... and they can observe the pin 16 will got the same signal... also the observe the Vcc got the voltage.

Would it be normal in our chip design? Because customer worried that should be the problem for their auto testing progress... please help to reconfirm it.

Thanks,

George

over 4 years ago

0 Hao L over 4 years ago

TI__Mastermind 25705 points

George,

I think this is normal since D pin has internal pull up and R pin has resistance path to Vcc too. Please let me know if you have more questions.

Regards,

Hao

0 George Liu1 over 4 years ago in reply to Hao L

TI__Intellectual 1570 points

Hi Hao,

Thanks for your reply, if they would like to avoid this phenomenon... is there any suggestion parts that pin and pin might be isolated?

Thanks,

George

0 Hao L over 4 years ago in reply to George Liu1

TI__Mastermind 25705 points

George,

If you need isolation, you can use the diode to block the current. I attach an app note about 3V MCU to 5V transceiver connection. The idea might apply to your case.

8484.3V MCU to 5V XCVR Interface.pdf

Regards,

Hao

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SN75C1167: Customer test the chip with UART signal, please help to confirm the behavior would be normal or not?