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ADS1298: AVDD power supply

anishp
Prodigy 60 points
Part Number: ADS1298
Other Parts Discussed in Thread: LP87702-Q1,

Hi,

I need help choosing a power supply for the ADS129x devices AVDD supply configured to use internal reference buffer. I'm assuming it needs an LDO supply for AVDD. We have a battery powered device and don't want an LDO burning power all the time. Is it okay to have a buck set to 3V with an LDO in series? We have chosen LP87702-Q1 (set to 3V) for the main supply and plan on adding a TPS73401DRVT LDO set to follow the input voltage after the LP87702-Q1 to provide a supply to the AVDD of the ADS129x. Is this okay to do?


Thanks,
Anish

  • 0
    TI__Guru 66436 points

    Hi Anish,

    Thanks for your post and welcome to our forum!

    Driving the AVDD supply with an LDO would be the preferred solution.

    The LP87702-Q1 appears to have an adjustable switching frequency. The clock input to the ADS1298 (or internal oscillator) would be 2.048 MHz, so try to stay away from multiples of that if possible. In addition, the ADC modulator is sampling at fMOD = 512 kHz (HR Mode) or 256 kHz (LP Mode). The digital filter response will repeat at multiples of fMOD, so aim for a switching frequency that will fall within the stopband of the digital filter for the most rejection.

    Hope this helps!

    Best Regards,

  • 0 in reply to Ryan Andrews
    Intellectual 385 points

    Hi Ryan,

    Will 3.6864MHz oscillator create any problem or is it good to go with it?

    www.digikey.com/.../6098133

    Thanks in advance.

    Regards,

    Rahul

  • 0 in reply to R_K
    TI__Guru 66436 points
    Hi Rahul,

    I don't see any issue with that particular frequency. 7 x fMOD = 3.584 MHz and 8 x fMOD = 4.096 MHz. Each multiple of the modulator frequency is at least 100 kHz away from your oscillator frequency, so any aliases should fold back into the digital filter stopband.

    Just to be clear - this oscillator is driving your switching supply frequency and not the CLK input pin of the ADS1298, correct?

    Best Regards,