OPA657

Khaled M. Dadesh

Prodigy 65 points

Other Parts Discussed in Thread: OPA657, OPA380

I am trying to operate the OPA657 as a trans-impedance amplifier, but I am not able to get it to work. any help

over 13 years ago

0 Luke LaPointe over 13 years ago

TI__Genius 13335 points

Khaled,

What specifically is not working? If you upload your schematic we can take a better look at the problem.

There are also a couple app notes that might help you get started:

Transimpedance Considerations for High-Speed Operational Amplifiers - sboa122
Compensate Transimpedance Amplifiers Intuitively - sboa055

Regards,
Luke Lapointe
High Speed Amplifiers

0 Khaled M. Dadesh over 13 years ago in reply to Luke LaPointe

Prodigy 65 points

Please refer to page 11 figure 3 in the datasheet of the OPA380. I am using the same schematic. I couldn't get it to work properly. I replace many of it, but every one gives different random and strange results. one of them gave 5V DC output modulated by my square wave light signal.

0 Luke LaPointe over 13 years ago in reply to Khaled M. Dadesh

TI__Genius 13335 points

Khaled,

Did you mean figure 3 of the OPA657 datasheet?

If so, the compensation capacitance could be an issue here. The feedback capacitor was chosen based on the input diode having a 50pF of capacitance. If this value changes, you will have to recalculate the value of the feedback capacitor again.

What is the capacitance value of your input diode?

Regards,
Luke

0 Georgy over 13 years ago in reply to Khaled M. Dadesh

Prodigy 100 points

Hi, Khaled

Try cleaning PSB with alcogol (CH2 H5 OH). On PSB may suffisient stray resistanse with dirt.

Regards!

0 Khaled M. Dadesh over 13 years ago in reply to Georgy

Prodigy 65 points

Hi Georgy,

Thank you for your advice. I was able to get it to work now, and it looks that there was soldering issues.

Regards

Khaled

Amplifiers

Amplifiers forum

OPA657