ADS7038-Q1: Minimum acquisition time calculation

Vishwas H R

Part Number: ADS7038-Q1

Tool/software:

Hello,

I am monitoring the DC voltage signal and using 1kR resistance and 100nF capacitor external to the ADC channel.

As per the video Driving SAR ADC without amplifiers (youtube.com) I have considered same formula and calculated the minimum acquistion time but I am negative value.

How to calculate tacq minimum here? Are there any other different approach?

6 months ago

0 Joel Meraz 6 months ago

TI__Expert 6790 points

Hi Vishwas,

Simply, an argument of the natural logarithm function that is less than 1 will give you a negative result. To solve this, we need the numerator to be greater than the denominator. In practice, this means decreasing the value of your C_filt value. Currently, it is much too high. A value such as 1nF should work better for this equation and for the accuracy of your system.

Regards,
Joel

0 Vishwas H R 6 months ago in reply to Joel Meraz

Prodigy 40 points

Hello Joel,

This formula is applicable only for continuous/ autonomous mode right? For the single shot conversion/ manual mode I could see the formula: tacqmin = Rfilt*(Cfilt+Csh)*ln(2). Here, I think it is fine to use bigger capacitance (100nF) as we get positive value and also periodically monitoring say 100ms once.

0 Joel Meraz 6 months ago in reply to Vishwas H R

TI__Expert 6790 points

Hi Vishwas,

At those rates, it should be okay to use a larger capacitor as you mentioned, but is there any other particular reason as to why you would opt to keep the capacitor in your design?

Regards,
Joel

0 Vishwas H R 6 months ago in reply to Joel Meraz

Prodigy 40 points

Hello Joel,

There is no particular reason we are just using for filtering the noise.

0 Joel Meraz 6 months ago in reply to Vishwas H R

TI__Expert 6790 points

Understood. Thanks for sharing!

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ADS7038-Q1: Minimum acquisition time calculation