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Original question:

ADS1158: ADS1158 Initialize Issue

ADS1158: ADS1158 Initialize Issue

Murugavel S
Prodigy 115 points
Part Number: ADS1158

Hi,

Thanks for your patience

Please find the attached waveform

When CS goes low before crystal stabilization, the ADC throw error (DOUT coming). Please find the attached waveform. Here the CS time is 715ms

So, we have increased CS time to 936ms. But, when we tune the CS pin timing, the oscillator time also getting extended without modifying the hardware. Please let us know the reason for it.

In this case, also the ADC throws an error. This issue is randomly coming. If the crystal stabilizes before CS goes low, this error did not come into the picture.

No error scenario:

Schematic:

 Regards,

Murugavel.S

  • 0
    TI__Guru 52316 points

    Hi Murugavel,

    Why are you toggling the CS pin while the oscillator has not stabilized? You should wait until the oscillator has settled before trying to communicate with the ADS1158, or the ADC operation might be undefined (which appears to be the case here).

    We have also observed that some other engineers have difficulty getting the 32kHz watch crystals to start oscillating. You can search e2e for many different threads covering this topic. It might be worthwhile to investigate using a discrete clock oscillator instead of a 32kHz crystal to avoid any intermittent clock behavior.

    -Bryan

  • 0 in reply to Bryan Lizon86
    Prodigy 115 points

    Hello Byran,

    Why the crystal doesn't have an identical stabilization time in all the scenarios?. 

    Does the CS pin impose on the crystal?.

    Kindly reply.

    Regards,

    Murugavel.S

  • 0 in reply to Murugavel S
    TI__Guru 52316 points

    Hi Murugavel,

    You might want to check out this app note about how the 32 kHz crystal works: https://www.ti.com/lit/an/slaa322d/slaa322d.pdf

    Given the tight constraints on the ability of the crystal to oscillate (and do so in a stable manner), it is possible that the load capacitance, trace capacitance, pin capacitance, crystal ESR, etc. are all shifting slightly over time and temperature making it more challenging for the crystal to consistently start-up. This has been the experience of many other engineers here on E2E. I would encourage you to consider using a discrete clock oscillator instead of a crystal with the ADS1158.

    Also, as mentioned previously, the ADS1158 needs a stable clock signal before you can start communicating with the device. This is shown in the Power-Up Timing section including Figure 37 and Table 6 in the ADS1158 datasheet. Please make sure the ADS1158 has a stable clock before communicating with the ADC.

    -Bryan