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ADS131E08: Integrated opamp not working.

Salavat Magazov
Prodigy 20 points

Part Number: ADS131E08

I am having problems with using integrated opamp. It is not producing correct signal despite being setup correctly.

config1 = 0x92

config2 = 0xE0

config3 = 0x45 (this should connect non-inverting input to OPAMPP pin and enable the opamp.)

I have verified that registers are set correctly by reading them back.

The gain of the opamp is setup to be 28. Inverting pin is connected to ground via 1k resistor. Non-inverting pin is connected to a 100 Ohm current sense resistor that drops 98mV. Output pin is connected to inverting pin via 27k resistor, which produces gain of 28. Output pin is also connected to VREFP and is meant to supply 2.744V of reference voltage.

Also, I found rather worrying thread https://e2e.ti.com/support/data-converters/f/73/t/614280, which contains no resolution.

  • 0
    TI__Guru 69196 points

    Hello Salavat,

    Welcome to our forum and thank you for your post.

    Can you share some details about the input and output voltage you are measuring in this configuration? Is the amplifier oscillating or do you simply see a DC error? The amplifier may not be stable driving a capacitive load directly.

    Also, keep in mind that the reference pin (VREFP) is sampled very quickly by a switch-capacitor circuit inside each ADC channel. This produces small transients which must be settled by the reference voltage driver. The OPAMP may struggle to do this adequately. The auxiliary op-amp inside the ADS131E08 is not intended to be used as a reference buffer. I don't believe the noise, offset, or drift specifications will be as good as the internal reference amplifier (which is why we don't specify them in the data sheet).

    Do you need to increase the reference voltage to accommodate your input signal range? If the internal 4-V reference is not accurate enough for your application, I would recommend using a 3-V external reference IC instead. 

    Regards,