Analogue input 40mv out.

[Scott Dev]

Hi

I am using a stm32L433 100 pin with an external 2.5v reference chip connected to vref+. I have tried placing a voltage (tried different values) onto one of the a/d channel, but the result is 40mv low. I then programmed the D/A , which uses the same VREF+ and tied it to the input channel of the A/D. The value on the D/A is what I expect, but the A/D channel is still reading 40mv too low. Anyone any idea what this may be?

Many Thanks

Scott

[waclawek.jan]

Missing or incorrectly performed ADC calibration (e.g. during VREF source startup or violated ADC voltage regulator startup time)? Too high signal impedance plus too short sampling time?

JW

[Scott Dev]

As I am using an external VREF (I have connected a 2.5v reference chip), I never done a calibration as I thought it was only for internal VREF?

Thanks

Scott

[waclawek.jan]

Okay, and if you stop thinking that?

JW

[Scott Dev]

"Okay, and if you stop thinking that?" , what does that mean?

I added the calibration and it worked, I just thought this was for calibrating the internal VREF when not using an external reference.

Thanks

Scott

[waclawek.jan]

> "Okay, and if you stop thinking that?" , what does that mean?

 That was in reply to your previous:

>> I never done a calibration as I thought it was only for internal VREF

trying to suggest to do calibration which you did and it apparently helped. Please mark thread as resolved.

JW

[Scott Dev]

It works well, I simply thought when using internal reference voltage this needed but not when using an external reference voltage

Scott

[Scott Dev]

How do you mark the thread resolved?