STM32L412: No decoupling caps for VDDA if not used?
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‎2020-11-28 4:55 PM
Hi there,
I'm designing an application with an STM32L412K8 and I don't use ADC, OPAMP or COMP. The datasheet (DS12469) says:
- VDDA shall be 0 to 3.6 V if ADC, OPAMP, COMP is not used (general operating conditions table 21).
- When the functions supplied by VDDA are not used, this supply should preferably be shorted to VDD (power supply schemes page 19).
Does this mean that I can just connect VDDA to VDD without any decoupling capacitors?
Thank you in advance!
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STM32L4 Series
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‎2020-11-28 6:13 PM
In STM32 designs VDDA typically powers the POR circuit, so if you're not using other analogue functions you can simply bond the supplies, and just retain any decoupling/bulk capacitance you have on VDD, serving the usual purpose, the CMOS switching currents/noise aren't going to trigger the POR.
Leaving VDDA unconnected is a primary cause of the part not starting as expected, as the NRST is clamped to GND
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‎2020-12-02 2:06 PM
Actually AN4555 tells that for L4 series POR/BOR, clocks and other mandatory "peripherals" are connected to VDD and VDDA is indeed only for ADC, DAC, OPAMP, COMP and reference buffer.
Anyway for both topologies the answer is yes.
