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ADS1299: ADS1299 voltage problem

ChiaHao Lee
Prodigy 60 points
Part Number: ADS1299

Tool/software:

1.When testing the ADS1299, I found that when the ADS1299 did not let PWDN and RESET pins go high, the AVSS was -2.49V, but after turning on PWDN and RESET, the AVSS dropped to -2.2~2.3V, so what could be the reason for this?
2.Is it necessary to add a 10K resistor between PWDN and VCC, and what is the purpose of that resistor?
3.When using the new ADS1299, vcap1 to gnd is the normal value -1.3V, but vcap3 to gnd will be floating value, about 0.4~1V, not long after the ADS1299 is bad, vcap1 to gnd will become AVSS, what may be the reason for this?

Fig1.-2.5V sch

Fig2. ads1299 sch

Fig3.PWDN、reset connect

Fig4. PCB (The white line is the -2.5V line.only connect ADS1299)

  • 0
    TI__Guru 60036 points

    Hi ChiaHao,

    Thank you for your post. You may have a power supply issue, which is loading current from your -2.5V source. Can you try replacing the -2.5V with an external power supply?

    The nPWDN and nRESET pins should be tied to DVDD with a 10kΩ pull-up resistor in order to establish the pin state at power-up. These are input pins to the ADS1299. If the voltage is not pulled-up to DVDD, then that means something else connected to those pins is holding the voltage low.

    If VCAP1 is changing from -1.3V to -2.5V (i.e. from +1.2V to 0V with respect to AVSS), that means the internal bandgap voltage is turning off. Likely this is caused by a power supply issue.

    Regards,

    Ryan

  • 0 in reply to Ryan Andrews
    Prodigy 60 points

    1.If nPWDN and nRESET are not connected to the 10k resistor, will there be any effect if they are connected directly to the DVDD?
    2.Does the internal bandgap voltage being off mean that the ADS1299 is damaged?

  • 0 in reply to ChiaHao Lee
    TI__Guru 60036 points

    Hi ChiaHao,

    1. The nPWDN and nRESET pins are inputs to the ADS1299 and do not draw much current. However, if the pins are also connected to your MCU, and the MCU GPIO pulls nPWDN or nRESET low, this will create a short-circuit from DVDD to DGND and collapse the digital supply (and may also damage the MCU pins). A 10kΩ pull-up resistor is intended to limit the current when nPWDN or nRESET is pulled low by the MCU.
    2. If the bandgap voltage powers on properly after power cycling the device, I do not believe there is any permanent damage. 

    Regards,

    Ryan