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STM32L476 minimal ADC sampling time

Uwe Bonnes
Principal II

Hello,

STM32L476 data sheet Rev 8 talks in 3.15 about "Down to 18.75 ns sampling time" while table 77 only lists a minimal 31.25 ns minimal sampling time. Is 18.75 ns sampling time possible and with what setting?

1 ACCEPTED SOLUTION

Accepted Solutions
KDJEM.1
ST Employee

Hello @Uwe Bonnes ,

Thank you for bringing this issue to our attention.

After checking internally with @InsignificantBit "18.75 ns sampling time" isn't correct.

The minimum sampling time is calculated as follows:

2.5 cycles / 80 MHz (max ADC frequency) = 31.25ns

So table 77 is correct, but this sentence “Down to 18.75 ns sampling time" is not correct.

Internal ticket number: 170685 (This is an internal tracking number and is not accessible or usable by customers).

Thank you.

Kaouthar

 

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.

View solution in original post

3 REPLIES 3
InsignificantBit
ST Employee

The 31.25 ns is indeed the shortest sampling time possible. The mention of 18.75 ns in the datasheet is indeed an error.

 

My previous reply was incorrect. I apologize for any inconvenience.

18.75 ns sampling time is possible, the 31.25 ns is the lowest time for which we provide some specifications in the datasheet.

How is it possible? SMPR registers have no published setting for a single sampling cycle. Or do you mean to overclock the CPU by 250 %.

KDJEM.1
ST Employee

Hello @Uwe Bonnes ,

Thank you for bringing this issue to our attention.

After checking internally with @InsignificantBit "18.75 ns sampling time" isn't correct.

The minimum sampling time is calculated as follows:

2.5 cycles / 80 MHz (max ADC frequency) = 31.25ns

So table 77 is correct, but this sentence “Down to 18.75 ns sampling time" is not correct.

Internal ticket number: 170685 (This is an internal tracking number and is not accessible or usable by customers).

Thank you.

Kaouthar

 

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.