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ADS1298: ADS1298

Konstantinos Petkos
Prodigy 100 points
Part Number: ADS1298

Hello,

I am using the analog to digital converter chip ADS1298 to record weak biosignals. I would like to introduce an instrumentation amplifier chip before the ADS1298 chip in order to achieve a better input referred noise for my system.

My ADS1298 chip supplies are: VREFP=+2.5V, VREFN=-2.5V and DVDD=+3.3V .

My question is whether or not the instrumentation amplifier I want to introduce before the ADS1298 chip must have the same supplies (+-2.5V) with the ADS1298 chip.

In other words, do you think that introducing an instrumentation amplifier with +-5V supplies before the ADS1298 would cause any problem to the function of the ADS1298  converter?

Thank you in advance,

Konstantinos

  • 0
    TI__Guru**** 168335 points
    Hi Konstantinos,

    The only concern I have with you providing +/-5V supplies to your INA that feeds into an ADS1298 inputs powered from +/-2.5V, is what might happen if the INA goes to one of the rails on it's output. You would then be supplying nearly 5V into the input of the ADS1298 that is powered from 2.5V, potentially over-driving the device and causing permanent damage. If you can power the INA from the same +/-2.5V, that would be great! If you can't, you should consider limiting the power to the ADS1298 inputs to less that 10mA.
  • 0 in reply to Tom Hendrick
    Prodigy 100 points

    Hi Tom,

    Thank you so much for your prompt reply!

    I totally understand your concern.

    However, since the ADS1298 is an AFE chip with PGAs before the actual ADC part, I would anticipate these PGAs to clip when the input voltage becomes +/- 5V and protect the actual ADC part (which is supplied with +/- 2.5V).

    Am I correct or am I missing something?

    Thank you again for your assistance,

    Konstantinos

  • 0 in reply to Konstantinos Petkos
    TI__Guru**** 168335 points
    Hi Konstantinos,

    The internal PGA's are also powered from the same +/-2.5V power rail as the ADC's. For the moment, just think of the ADS1298 as a block box with +/-2.5V power applied. If you drive the inputs to +/-5V without current limiting the source, you run the risk of damaging the device. Please note the 'Absolute Maximum Ratings' (Table 7.1, page 12) for the Analog input voltage. The limitation is +/- 300 mV over the supply rails or +/- 2.8 V when powered from +/- 2.5V power supplies.
  • 0 in reply to Tom Hendrick
    Prodigy 100 points
    Hi Tom,

    Thank you for your reply.

    Everything is clear now.

    Best regards,
    Konstantinos