TRS3122E: DOUT not to spec

AndreyL

Part Number: TRS3122E

TRS3122E is outputting the RS-232 signal on pin 5 bellow the spec - 2.65*VCC (1.8V) and the slew rate is way off, baud rate is 57600. Data in works fine.

over 8 years ago

0 Hao L over 8 years ago

TI__Mastermind 25705 points

AndreyL,

Can you check the charge pump output (V+ pin 20, V- pin 24) setup one more time? They both need to have a 100nF capacitor to ground when Vcc is below 2V.

Plesae let me know if you have more questions.

Regards,

0 AndreyL over 8 years ago in reply to Hao L

Prodigy 40 points

I checked everything again and it all looks good, I desoldered the caps and checked the values all 100nF. I also tried doubling them in parallel. Still the outputs are not trippling and the slew rate is two bits long on the negative going pulse.

0 AndreyL over 8 years ago in reply to AndreyL

Prodigy 40 points

Is there a better functional diagram than the one in the datasheet?

0 AndreyL over 8 years ago in reply to AndreyL

Prodigy 40 points

I found the issue. V+ cap was connected to 1.8V. It should have been isolated.

0 Hao L over 8 years ago in reply to AndreyL

TI__Mastermind 25705 points

Great. In general when you debug an issue for RS232 devices, you start from V+ and V- to see if the charge pump output is expected. If you have further questions, please let me know.

Regards,

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TRS3122E: DOUT not to spec