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STM32L4 opamp to ADC constraints

Question asked by Yan Méroth Employee on Jan 11, 2018

Hi,

My stm32 opamp characteristics understanding is that

- max output current 500µA in normal mode, stand-alone

- min output impedance 4kR in normal mode, stand-alone.

This last value fairly aligns to considering a serviceable output impedance corresponding to 3.6V/2 / 500µA.

 

As a consequence, when one routes opamp output (standalone+normal mode) into ADC input, it means that sample rate should a Rain above 4k. Do i get it right?

For example, for ADC running at 80MHz and 12 bit resolution :

  • (fast channel) min usable Rain_max = 4,7k
    Corresponds to selecting min 92.5 sampling cycles
    Results in anti-aliasing required cut-off at Fs/2 = ~380kHz max
  • (slow channel) min usable Rain_max = 10k
    Corresponds to selecting min 247.5 sampling cycles
    Results in anti-aliasing required cut-off at Fs/2 = ~154kHz max

 

Regards,

Y.

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