TRS232E: What happens if the TRS232E device is connected to 100nF capacitors instead of the recommended 1uF?

USO

Part Number: TRS232E

We replaced the obsolete LMS202ECM/NOPB devices on our BOM a while back with the TRS232ECD/ECDR/EID/EIDR.

We have been having some intermittent issues connecting to our RS-232 port at 9600baud.

Just noticed on the datasheet that the caps are recommended to be 1uF and not 100nF which we had been using with the LMS202ECM previously.

Do you have any details on what the expected result would be from using 100nF caps? Could that explain the intermittent issues we have been having?

Thanks

over 4 years ago

0 USO over 4 years ago

Intellectual 271 points

Just wanted to add that we had previously tested that the device worked with 100nF caps at 9600 baud and 115.2k baud, but recently we've had some that sometimes are not connecting and then work after a subsequent power up and we cannot get it to fail again after.

0 Hao L over 4 years ago in reply to USO

TI__Mastermind 25705 points

Hi,

The device should work with 100nF instead of 1uF cap. You can refer to this blog for the discussion. The ratio between the caps matters more than the absolute value.

e2e.ti.com/.../how-the-rs-232-transceiver-s-regulated-charge-pump-circuitry-works

Does the device stop working in middle of communication and need power cycle? It would be helpful if you capture some waveforms of the bus pins and V+/V- if the issue happens again. Please let me know if you have more questions.

Regards,

Hao

0 USO over 4 years ago in reply to Hao L

Intellectual 271 points

Thanks for letting us know that it should work with 100nF and the link to the article.

Turns out the issue wasn't related to the device and the UART just wasn't getting initialized.

We'll dig deeper if there are further issues.

Thanks again.

Interface

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TRS232E: What happens if the TRS232E device is connected to 100nF capacitors instead of the recommended 1uF?