STM32L011E4 ADC input impedance

[KaneTW]

Hi,

the STM32L011E4 has a R_ADC of 1kOhm max according to the datasheet. Does this hold true for standard channels as well, or do standard channels have a higher impedance? The table with R_AIN_max isn't super helpful in this regard as my calculation results don't match with either standard or fast channels.

AN2834 mentions an ADC sampling estimation tool. Is it possible to acquire it?

Best regards,

David Kraeutmann

[Peter BENSCH · Accepted solution]

Welcome, @KaneTW​, to the community!

The max. 1kohm of the RADC is the sampling switch resistance, whose influence can be seen in Fig. 28 of the data sheet. It can be used with equation 1 in the calculation of the RAIN occurring externally.

The input impedance RAIN relevant for the external circuit is in fact max 50kohms, so that for maximum measuring accuracy and/or adaptation to the measuring signal, an operational amplifier is typically driving the ADC input as an impedance converter.

There is no charge for the Sampling Estimation Tool, but it is only provided on a controlled basis. Please contact your nearest distributor or FAE contact at STMicroelectronics.

Does it answer your question?

Regards

/Peter

[KaneTW]

Thanks! I'll get in touch with my distributor.

[Peter BENSCH]

Great!

If the problem is solved, please mark this thread as answered by selecting Select as best, as also explained here. This will help other users find that answer faster.

Good luck!

Regards

/Peter