OPA350: OPA350

Folkert de Jong

Part Number: OPA350
Other Parts Discussed in Thread: LM7705

Hi. I am referring to the following remark in the forum (Sep 7, 2017) about using an OPA350 in a photodiode transimpedance amplifier:

"Also, please be aware that since OPA350 output can only swing linearly within 50mV above its negative rail, under the dark current condition (no current in diode) for the circuit to work properly, you may NOT power the circuit from a single supply."

My questions: Why is that so and what would be a proper/advisable power supply, for example Vcc- -1V and Vcc+ +4V ?

Thanks,

Folkert

over 4 years ago

0 Michael Steffes over 4 years ago

Guru 47485 points

Yes, most of these RRO devices need some small headroom to operate close to ground on the output in single supply, the LM7705 was intended to provide that small negative supply

0 Raymond Zhang1 over 4 years ago in reply to Michael Steffes

TI__Mastermind 47716 points

Hi Folkert,

My questions: Why is that so and what would be a proper/advisable power supply, for example Vcc- -1V and Vcc+ +4V ?

Answer:

There are no big advantages to place wider voltage rails in OPA350, if you want to keep Vout/Iin operating in linear region. I will recommend to keep V- slightly negative biased (-0.5 to -1V or so) and V+ is what is available on your board with V+ < 5.5V, see the captured image below.

I think that there is a "typo" in the Input common mode Voltage range, which it should have been (V-)-0.1 rather than -0.1V. However, the section 6.6 in the datasheet is using the single voltage rail when the data was obtained, therefore -0.1V is also correct in that content, since V- = 0 = GND.

Best,

Raymond