Hello guys, I bought an op amp from mouser, the LMP7721 (data sheet below).

I have been testing it, I soldered it to a break out board.

after connecting 3.3v supply from an arduino uno to v+ and v- and connecting in- to vout I measured between ground and in+ 1.2 to 1.8 V.

if I disconnect vout from in- , vout shows 0v
And both in- and in+ show 1.2 to 1.8 V.

can I assume that the op amp is broken?

ps ( I actually bought 2 LMP7721 but I’m waiting on desoldering alloy to be able to switch the other one with the one is in the break out board).

Any way, I hope some one can help me, I am grateful for any assistance.

link to data sheet:
https://www.ti.com/lit/ds/symlink/lmp7721.pdf

 

Hello guys, I bought an op amp from mouser, the LMP7721 (data sheet below).

I have been testing it, I soldered it to a break out board.

after connecting 3.3v supply from an arduino uno to v+ and v- and connecting in- to vout I measured between ground and in+ 1.2 to 1.8 V.

if I disconnect vout from in- , vout shows 0v
And both in- and in+ show 1.2 to 1.8 V.

can I assume that the op amp is broken?

ps ( I actually bought 2 LMP7721 but I’m waiting on desoldering alloy to be able to switch the other one with the one is in the break out board).

Any way, I hope some one can help me, I am grateful for any assistance.

link to data sheet:
https://www.ti.com/lit/ds/symlink/lmp7721.pdf

The language of electronics is the schematic – not English.

 

can I assume that the op amp is broken?

No. You cannot measure input voltages directly because the inputs have very high input impedances.

Show us a diagram of your test circuit.

Here are two simple test circuits:

 

No. You cannot measure input voltages directly because the inputs have very high input impedances.

Show us a diagram of your test circuit.

Here are two simple test circuits:

View attachment 316361

Hi MrChips, just wanted to thank you for your help, I tested the op amp with the non inverted circuit you showed ant it is working now.
I assumed that when there is no input to the op amp it would out put 0v but apparently it doesn’t work predictively when there is no input.

 

It is a newcomer mistake to think that when there is no input it is at 0V.
This is not the case for high impedance inputs on analog and digital circuits.
A high input impedance means that the input is an antenna that can pick up every radio, TV, cell phone, bluetooth and 50Hz/60Hz AC line voltage signal.

 

after connecting 3.3v supply from an arduino uno to v+ and v- and connecting in- to vout I measured between ground and in+ 1.2 to 1.8 V.

Why are you measuring the voltage at a floating input? That is meaningless. Connect the input to a known voltage and measure the output.