LMV321-N-Q1: OPA output capability and compared with OPA2365

JiaJie Lin

Prodigy 20 points

Part Number: LMV321-N-Q1
Other Parts Discussed in Thread: OPA2365, LMV321, TLV6001-Q1

Hi,

I'm used LMV321-N-Q1 for PFC input voltage feedback.

OPA supply voltage is 3.3V.

When opa input is 110v, the output voltage be clamped arond 2.06v.

(CH1: OPA input CH2 : OPA output CH3:OPA supply voltage)

But if OPA supply voltage increase to 3.5v, the output voltage match the OPA setted gain.

I also tried to change OPA to OPA2365, the opa output is correct and don't need to change supply voltage to 3.5v or other.

Does the OPA's output capability is affected by supply voltage?

My english is not good, sorry.

over 2 years ago

+1 Clemens Ladisch over 2 years ago

Guru 283290 points

The LMV321 does not have rail-to-rail inputs; input voltages must stay 1 V below the positive rail.

The OPA2365 does have rail-to-rail inputs (and outputs). There are many other opamps with this feature, e.g., TLV6001-Q1.

+1 kai klaas69 over 2 years ago

Guru 140200 points

Hi Jiajie,

the circuit should work, until the signal voltage at the +input of LMV321 reaches 2.3V which would be the common mode input voltage limit here (3.3V - 1V = 2.3V), as Clemens already mentioned:

jia_lmv321.TSC

But your circuit has a massive stability problem caused by the 1nF cap mounted from the -input of LMV321 to ground:

If you want to add low pass filtering, then do it this way:

Also remove the 100pF cap between the inputs of LMV321. This can also destabilize the circuit.

Kai

0 JiaJie Lin over 2 years ago in reply to Clemens Ladisch

Prodigy 20 points

Thank you.

0 JiaJie Lin over 2 years ago in reply to kai klaas69

Prodigy 20 points

Thank you.

Because of the holidays, TI E2E™ design support forum responses will be delayed from Dec. 25 through Jan. 2. Thank you for your patience.

Amplifiers

Amplifiers forum

LMV321-N-Q1: OPA output capability and compared with OPA2365