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ADS131M08: using different PGA gain value for sensing the same signal

Jack Tan80
Mastermind 7130 points
Part Number: ADS131M08

Dear ADC expert,

Below picture shows one of my real application of sensing battery voltages. In order to have high accuracy in sensing low voltage, I connected the same sense signal into 3 different channels, and use different PAG GAIN values for each channel. PGA GAIN0 is 1 for channel 0, PGA GAIN1 is 2 for channel 1, PGA GAIN7 is 4 for channel 7.

My question is that:

  1. When sense signal is 1V for all channels, I will use adc result from channel 0. However, the delta sigma adc input signal voltage of channel 2 and channel 7 are 2V and 4V respectively , which is out of range of ADC, but the pins voltage of channel 1 and channel 7 are still 1V, will it be cause the ADC damaged in this case?
  2. When sense signal is in low volage, for example, sense signal is 0.2V, I use the adc result from channel 7, is it able to increase the sense accuracy if using channel 7 compared with channel 0?

Regards,

Jack

  • 0
    TI__Mastermind 45805 points

    Hi Jack,

    1. Your gain should be considered when you converted your code to input voltage. The PGA gain scales the differential full-scale range (FSR), when your gain is changed from 1 to 2 or 4, your FSR has actually been changed from ±1.2V to ±600mV or ±300mV. You will get correct input voltage once your gain is considered.

    2. Using a gain on CH7 will not be able to increase your accuracy. Using a high gain at the same data rate actually reduces the effective resolution and noise free resolution of ADC. See the table 7-2 and the 7.1 section in M08 datasheet.

    Regards,

    Dale