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ads1241 Power On Reset problems

John Schimandle
Intellectual 390 points
Other Parts Discussed in Thread: ADS1241

Using the ads1241 on a number of boards with a number of different power configurations. On one of these boards the ads1241 sometimes comes up in a mode where it is does not digitize the signal correctly and results in digital codes that are too low. If you power cycle the board then the part usually works correctly. Looked at a number of power up issues including the power supply ramp and ~reset and these all look OK to me. The data sheet is not really clear as to what the different resets actually do. There are three ways to reset the chip.

1. assert the reset pin for at least the number of oscillator cycles specified on the data sheet

2. Use the special SCLK signalling sequence

3. write the RESET command (0xFE) to the SPI interface

The data sheet also says the special SCLK signaling sequence resets the entire chip but is not really clear as to what that includes.

Can someone provide some clarity about the different resets.

Regards,

John

  • 0
    TI__Guru** 113765 points

    John,

    The biggest problem with power up is having enough available current so that when the device starts to turn on the supply voltage doesn't dip.  The hardware reset is always the best way to go for reinitialization.  The downside is it requires a pin from the micro if you want to control it.  Some place a power supervisor on the reset pin to make sure that the supply is valid before the device initializes.

    As I recall the SCLK pattern will do a POR, but the RESET command only resets the digital portion and registers.  I will have to look through the documentaion and try to verify this and respond as soon as I get a chance.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Intellectual 390 points

    Bob,

    Any progress on the SCLK pattern POR.

    Also, are there any problems with power supply ordering in the bring up. In this design the AVDD and Vref comes up before the VDD.

    Regards,

    John

  • 0 in reply to John Schimandle
    TI__Guru** 113765 points

    John,

    I've been searching through the documentation and all three modes reset the digital/analog portions.  However, it does not appear that a full power on reset occurs as this would require restarting the oscillator and reinitializing the state machine while resetting.  Hope that makes some sense.  I will keep digging and let you know more as soon as I find more detail or can actually test the device.

    As far as supply sequencing, bringing up the analog portion before the digital should not be an issue as the digital will reset the analog system when it does the POR.  I will verfiy this and let you know about this as well.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    TI__Guru** 113765 points

    John,

    Here is what is different about the various resets.  The reset SCLK pattern resets the analog/digital circuitry and registers only.  The reset command adds to the former by also resetting the clock generator circuit.  The reset pin adds to the reset command functions by also resetting the oscillator.  So the fullest reset is by using the reset pin.

    As the POR resets all the above mentioned, turning on the digital supply after the analog supply resets the entire device for proper operation.

    Best regards,

    Bob B