STM32 NUCLEO-L476RG OPAMP Output not below 1.4 V

Forum|Forum|8 years ago
March 26, 2018
1 reply
2278 views

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

This topic has been closed for replies.

waclawek.jan

Super User

Posted on March 26, 2018 at 18:45

What's the load on the output of opamp?

JW

cyancaliAuthor

Associate II

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

Super User

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

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