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ADS131E06: VCAP1 charging start timing

Shota Mago
Expert 8830 points

Part Number: ADS131E06

Hi team,

My customer will use ADS131E06 for his application and he is adjusting timing of RESET after PoR.

Although he thought VCAP1 would be charged immediately after power-up of supplies, there is about 400ms delay for start of charging as this waveform(VCAP1.png) which can be accessed via TI internal network.

CH1: Power_EN

CH2：VCAP1

CH3：RESET

Please ignore 1st glitch of supplies/RESET. This is caused by instrument side.

Also, he will add additional 800ms delay for RESET from setup of the wavefrom.

Why start of VCAP1 charging shows delay?

Is it expected behavior?

Additionally, about 100mV voltage remains on VCAP1 even after power down.

Is this correct behavior(is this just matter of capacitor side)?

Best regards,

Shota Mago

Best regards,

Shota Mgo 

  • 0
    TI__Guru 68966 points

    Hello Mago-san,

    Thank you for your post.

    What is "Power_EN"? I imagine it could be a control signal to an enable pin on an LDO or some other IC. It would be more appropriate to look directly at the time between AVDD = ON and VCAP1, measured at the device pins. 

    The 100 mV on VCAP1 during power-down could be due to slight measurement error. Are you measuring with respect to AVSS or ground somewhere else on the board? Or, like you mention, the capacitor could be holding a charge and influencing the measurement during power-down.  I don't think it's a significant concern.

    Regards,

    Ryan 

  • 0 in reply to Ryan Andrews
    TI__Expert 8830 points

    Hi Ryan-san,

    Sorry for lack of explanation. I forgot to add meaning of Power_EN.

    As you expected, it means EN signal for LDO which powers AVDD/DVDD.

    I'll ask the customer to measure AVDD directly but he just would like to know condition which triggers charging of VCAP1.

    Noted for 100mV during power-down would not be significant concern.

    Best regards,

    Shota Mago

  • 0 in reply to Ryan Andrews
    TI__Expert 8830 points

    Hi Ryan-san,

    Although I've not received new captured waveform which includes direct AVDD and VCAP1 measurement, would it be possible to provide condition to start charging VCAP1?
    Once AVDD powered up, is VCAP1 supposed to be charged immediately?

    Best regards,

    Shota Mago

  • 0 in reply to Shota Mago
    TI__Guru 68966 points

    Hi Mago-san,

    I have asked the designer to look into it. I will reply with an update shortly.

    Regards,

    Ryan

  • +1 in reply to Ryan Andrews
    TI__Guru 68966 points

    Hi Mago-san,

    VCAP1 is expected to start ramping as soon as the power supplies turn on. Perhaps the customer is holding the /PWDN pin low during the first 400 ms?

    Regards,

    Ryan

  • 0 in reply to Ryan Andrews
    TI__Expert 8830 points

    Hi Ryan-san,

    Thanks for your confirmation.

    Since the customer controls /PWDN pin, he will check if there is any delay or not.

    Best regards,

    Shota Mago