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Original question:

ADS1299: Not sure if the internal reference is working properly....

ADS1299: Not sure if the internal reference is working properly

praga vipul
Prodigy 60 points
Part Number: ADS1299

Hello Alex, 

So i replaced the chip , and now the vcap1 volatage is correct, but the 4.5v between VREFP and VREFN is not there, I did check with the ads1299EVM board for our mux settings via our micro-controller board and that works fine. When we read back the mux settings in our ADS1299 pcb , the mux settings are correctly written but the voltage is not generated between VREFP and VREFN. 

  • 0
    TI__Guru 66466 points

    Hello Praga,

    Is the internal reference buffer enabled?

    Regards,

  • 0 in reply to Ryan Andrews
    Prodigy 60 points

    Hello ryan, 

    yes they are. As i mentioned above the code works fine with the ads1299 EVM kit(daughter board) together with our microcontroller

  • 0 in reply to praga vipul
    TI__Guru 66466 points

    Hi Praga,

    Thanks. I understand the code has proven to work, but please add an extra step to read back all register values and list them here. We are specifically interested in the CONFIG3 register. This register is independent of the channel MUX settings you referred to initially.

    VCAP1 is an internal bandgap voltage used to derive the internal reference voltage. If VCAP1 is correct (AVSS + 1.2 V) and the reference buffer is enabled, I cannot see a reason why the reference voltage could not come out correctly.

    Best regards,

  • 0 in reply to Ryan Andrews
    Prodigy 60 points

    Hello Ryan, 

    We did the test again today, while the AVSS being -2.5v and AVDD being +2.5v (with respect to battery negative)

    The following were the voltages with respect to battery negative which is 0v. 

    VCAP 1 - 1.3v

    VCAP 2 - 345mv 

    VCAP3 - 3.6v

    VCAP4 - (-2.3v)

    we wrote and read the config 3 registers, which is correct. but the internal reference was at 400mV., 

    so we tried the external reference via a precision supply set at 4v  and current limiting at 0.001A, was supplied, but the voltage dropped down to 400mV. 

    so we measured the impedance across VREPP and VREFN and following were the results, 

    when activating internal reference via config3 - 132 ohms 

    when internal reference was switched off via config 3 - 400 kohms

    I really dont see any issues in the settings or the PCB , could the impedance measurement results denote an internal damage is there ? 

  • 0 in reply to praga vipul
    TI__Guru 66466 points

    Hello Praga,

    The VCAP bias voltages you mentioned are all positive except for VCAP4? Just to clarify, you measured the following with respect to GND (0V):

    • VCAP1 = +1.3V
    • VCAP2 = +345mV
    • VCAP3 = +3.6V
    • VCAP4 = -2.3V

    VCAP1 = +1.3 V (with respect to GND) is too high. We except VCAP1 = AVSS + 1.2V. For your bipolar supply setup, VCAP1 should measure -1.3V (negative with respect to GND). Try toggling the /RESET pin after power is applied to the device. If this does not restore the correct bias voltages, the device may be damaged.

    Regards,