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ads1110

siauhwa ong
Expert 1510 points
Other Parts Discussed in Thread: ADS1110

Hi,

I have a problem with ads1110, the I2C SCL seems to pull the voltage down all the time. That was after everything was working properly for a few days.

The ads1110 is powered up every 30 minutes and will keep powering on for about 2 seconds (during which all measurement are taken)  and then powered off.

Do you have any idea why it failed ?

Or any idea to improve it considering the way ads1110 is power on and off regularly every certain period.

Thank you

  • 0
    TI__Guru* 92655 points

    Siauhwa,


    I would first check to see if this isn't a problem with the device you are using as the I2C master. For the ADS1110, the SCL pin is an input only. The SCL pin has no output drive capability and can only respond as a digital inputs.

    If you have a scope shot of SCL and SDA it might help with the debug. If there is something with a weak pull-down, you might still see some SCL response, even if it is small.


    Joseph Wu

  • 0 in reply to Joseph Wu
    Expert 1510 points

    Hi,

    It's definitely due to ads1110, it's fixed after replaceing ads1110.

    My real question was : is there any problem for switching on and off the ads regularly for ex every 10 minutes or so...
    Any idea to improve reliability?

    Pull up Resistors  are 4K7 Kohms, by the way

    Thank you

  • 0 in reply to siauhwa ong
    TI__Guru* 92655 points

    Siauhwa,


    There should be no problem switching on and off the ADC on a regular basis, the only problems that I can think of are associated with the power supplies.

    I would make sure of two things if you are turning the power supplies. First, make sure that there is enough time for the power supply to settle to final value the supply comes up so that the reference settles to the final value. Second, I would makes sure that the power supply comes up cleanly each time. If there are power supply spikes, you want to make sure that they do not exceed the absolute maximum ratings of the device as shown on page 2 of the datasheet (pins should not exceed 6V). If the absolute maximum ratings of the device are exceeded, this could cause damage to the device and cause it to fail.

    If you are having problems with the latter problem, you may want to get a scope photo of the VDD line when the device is powering on.


    Joseph Wu

  • 0 in reply to Joseph Wu
    Expert 1510 points

    Hi Joseph,

    Any idea on how to achieve that in practive  / circuit ?

    Thank you

  • 0 in reply to siauhwa ong
    TI__Guru* 92655 points

    Siauhwa,

    There are a couple things that I would look for.

    First, generally, I don't like to have inductors in the power supply path for digital circuits (including ADCs). With digital switching, the large change in current will usually cause a large change in voltage with any kind of digital switching. Decoupling caps close to the device VDD can help with this, but if the supply spikes are large, you may need more protection (like some sort of TVS).

    Second, if there are large caps on the input, there may be a large amount of charge being stored on the inputs that can get pushed into the inputs when the device is being turned off. I'm not sure if this is a big problem, but it was commented on by a couple of my colleagues here.

    If you have a schematic that you'd like to share, I'd be happy to look at it. If you don't want to show it publicly, I can look it over through an email. Let me know and I'll email you back.

    Joseph Wu

  • 0 in reply to Joseph Wu
    Expert 1510 points

    Hi Joseph,

    I'll look at the TVS solution.

    By the way,  when you said about the large capacitance on the input, do you mean large capacitance on the input of the ADS1110 ?

    In my case, I don't have such capacitance. The input the ADS1110 is directly connected to op-amp output (2 op-amps configured as instrumentation amp).

    And yeah, would you mind to give me your email.

    Thank you

  • 0 in reply to siauhwa ong
    TI__Guru* 92655 points

    Siauhwa,

    I'll contact you directly and take this post offline. However, I may not be able to get back to you until Monday.

    Joseph Wu

  • 0 in reply to Joseph Wu
    Expert 1510 points

    Hi Joseph,

    I just emailed you the schematic. Please check them if you have a chance.

    Thank you