STM32 NUCLEO-L476RG OPAMP Output not below 1.4 V

[cyancali]

Posted on March 26, 2018 at 17:00

Hey guys,

i am right now working on the Nucleo L476 RG Board. I generated source code with STM32CubeMX (v4.25). I am using the internal opamp in 'Follower' mode and reading the output with the on-board adc. VCC is 3.3 V.

When applying different voltage levels to the input of the internal opamp i have seen that the opamp output never goes below 1.4 V even when i directly short the input to GND. Above 1.4 V everything works like expected.

Does anyone have a clue what is going wrong/missing in the code to make it work over the full spectrum?

Thank you and best regards,

Alex

[waclawek.jan]

Posted on March 26, 2018 at 18:45

What's the load on the output of opamp?

JW

[cyancali]

Posted on April 06, 2018 at 12:48

The only load on my opamp output is my mutlimeter. But I think i figured something out.. Luckily on the MCU is a second OpAmp, i switched to it and it works now!

At the beginning the default setting for Power Supply Range was set to 'Low', but I am powering it with 3,3 V. I have seen the wrong setting after the first tries and changed it to 'High'. Is there a chance i fried OpAmp1 with a wrong setting in the register? Thank you for your help!Alex

[waclawek.jan]

Posted on April 07, 2018 at 17:00

If by Power Supply Range you mean setting of OPAMP1_CSR.OPA_RANGE , I don't think it in itself may cause damage to the opamp. According to the datasheet, its effect is to change the gain-bandwidth product, and the desctiption in RM hints that this is done because of the opamp's stability. Thus, it might have oscillated at the higher supply voltage, but I don't believe that would have catastrophic effects.

JW