2023-11-06 03:36 PM
I have VREFBUF configured for output to comparator on my board. I see this on MCU Vref+ pin...
VREFBUF_CSR = 0x09.
Solved! Go to Solution.
2023-11-08 05:57 AM
Hello,
You can check the Errata sheet :
The pull-down resistor on VREFBUF output is missing, thus causing a slow discharge of the capacitor on the
VREF+ pin.
Workaround :
When switching down the VREFBUF output, wait for a sufficient time to discharge of the capacitor connected to
VREF+ pin.
Foued
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2023-11-07 06:56 AM
The waveform above does not appear until I set ENVR in VREFBUF_CCR. No GPIOs active.
There is no 1.2MHz coming from the board.
Does this waveform mean that Vrefint is not steady? If yes, this would seem bad news for ADC accuracy.
2023-11-07 10:14 AM
I don't know specifically about the H5 series chips, but generally, yes, you need external caps on the VREF+ pin for stability. For the F4xx ST recommends 1uF and 100nF in parallel.
2023-11-08 05:57 AM
Hello,
You can check the Errata sheet :
The pull-down resistor on VREFBUF output is missing, thus causing a slow discharge of the capacitor on the
VREF+ pin.
Workaround :
When switching down the VREFBUF output, wait for a sufficient time to discharge of the capacitor connected to
VREF+ pin.
Foued
To give better visibility on the answered topics, please click on Accept as Solution on the reply which solved your issue or answered your question.
2023-11-10 12:41 PM
Moving caps as close as possible to MCU (mentioned in DS14258 under General PCB design guidelines) fixed this for me.