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gregstm
gregstm
Senior II
May 11, 2019
Question

STM32L4.. fs=10Ksps ADC Current, how do you get the stated 16uA?

  • May 11, 2019
  • 4 replies
  • 972 views

In the data sheet it states that the ADC current at fs=10Ksps is 16 microAmps. I'm struggling to get the current that low. Even just switching on the ADC and its regulator exceeds that value

My application has a mode where I need the ADC data passed through to the DAC (unchanged) with the lowest current possible (coin cell application). Sample rate is 16,384Hz derived from TMR2 (with LSE=32,768Hz). I trigger the ADC with TMR2 and DMA the result straight to the DAC. The system clock is MSI=1 MHz , with the CPU in LPSLEEP.

Anyway, since this 10Ksps= 16uA is stated in the data sheet, I thought maybe the ST engineers could state how this current consumption could be achieved,

thanks

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4 replies

Mohamed Aymen HZAMI
Mohamed Aymen HZAMI
ST Employee
May 16, 2019

Hello,

Can you please share with us the configuration that you use.

Best Regards,

Mohamed Aymen.

gregstm
gregstmAuthor
Senior II
May 19, 2019

Thankfully I think I have figured out what is going on.

It is not the ADC, drawing the unexpected current - it is the DAC. I didn't realise that the DAC consumes different amounts of current depending on what value is written to the DAC . I did my initial current tests with the DAC value/code = 0, this seems to consume minimal current. When the analog power is enabled the, DAC is mainly around a value of 2048. This DAC value seems to consume around 200 uA more. (I configure the DAC to have the Buffer=OFF, I write directly to the registers for configuration)

I would be curious to know if there is a formula to calculate the DAC current consumption for a given DAC value/code.

thanks.

S.Ma
S.Ma
Principal
May 19, 2019

Welcome to the analog world. Consumption will depend on the analog impedence of what you drive as circuitry

gregstm
gregstmAuthor
Senior II
May 19, 2019

Thanks - the Analog world is interesting. I'm pretty sure the power consumption variation is of the DAC itself, that is, the internal R-2R resistance ladder. The amplifier I was driving during testing has a 4pA input bias current - and the DAC was just set to a constant value/code during current tests. When I load another board later I will re-confirm current measurements with just the micro only loaded.

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