This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ADS124S06: ADS124S06 Power-on-reset at supply voltage drop

Part Number: ADS124S06
Other Parts Discussed in Thread: ADS1248

Dear Sir,

At section 9.4.1.1 on page 59 of d/s, it has the following description:

"a brown-out event occurs, when the supplies have dipped below the minimum operating voltages."

Does it mean that three AVDD(to AVSS), DVDD(to DGND) or IOVDD(to DGND) voltages are monitored and  if even only one of them is detected below MIN voltage, it goes into POR?

And above DVDD in IOVDD to GND means IOVDD < DVDD? It is NOT 2.7V but 3.3V when DVDD=3.3V?

Operation condition is specifically 

AVDD=5V

DVDD=IOVDD=3.3V

AVSS=DGND=0V

Best regards,

Masa

  • Hi Masa,

    The ADS124S06 uses 3 supplies for operation. One is the analog supply (AVDD/AVSS which can be either unipolar or bipolar) and there are 2 digital supplies DVDD (which is the digital core supply of the ADS124S06) and IOVDD (which is the IO supply for communication). All supplies must be at nominal operating voltages before the ADS124S06 can be used. The DVDD voltage can range from 2.7V to 3.6V, but IOVDD must be at least the same voltage as DVDD, but can extend up to 5.25V if the IO voltage needs to be greater than the DVDD voltage. In most cases DVDD and IOVDD will be the same voltage and is often 3.3V. The minimum operating supply range is 2.7V.

    The Power-On Reset is discussed on page 59 of the ADS124S06 datasheet in section 9.4.1.1. All voltages are monitored for proper operation. The startup POR threshold is approximately 1.65V. Once all supplies have passed the threshold, the device will set the FL_POR bit as a status flag in the STATUS register. This bit should be cleared after the device is ready to use so that if a brown-out should occur and a reset takes place due to the brown-event, the status flag FL_POR will be set as an indicator.

    Best regards,
    Bob B
  • Hi Bob,
    May I confirm what is the condition of the brown-out during normal operation after FL_POR was cleared?
    I would like to make sure each supply under voltage condition, and one (not all) of three brown-event makes FL_POR on again (error)?

    Best regards,
    Masa
  • Hi Masa,

    There are 2 critical supplies that affect the device settings and register data. These are the analog supply (AVDD/AVSS) and the digital core supply (DVDD). If either (or both) of these supplies brown-out, the FL_POR flag will be set.

    The IOVDD supply is a little different in that the supply voltage does not directly impact the internal operation of the ADS124S06 from a device setting perspective. If the DVDD supply is working properly and the IOVDD has a brown-out event the DVDD supply will attempt to back drive the IOVDD supply as the supplies have an internal connection (similar to a diode connection). This will increase the DVDD current which is one of the reasons why IOVDD should never go below DVDD in voltage as given in the table in section 7.3 of the datasheet.

    In the use case you have given, where IOVDD and DVDD are tied together, then IOVDD and DVDD will brown-out together. If a brown-out event should occur on the 3.3V supply the FL_POR flag will be set.

    So if the 5V supply has a brown-out the FL_POR flag is set. If the 3.3V supply has a brown-out event the FL_POR flag will be set. If both the 5V and 3.3V supplies have a brown-out event the FL_POR flag is set. I hope this explanation makes the operation more clear.

    Best regards,
    Bob B
  • Hi Bob,
    Thank you very much for your explanation.
    But I would like to know what is each threshold voltages of under-voltage detect for AVDD and DVDD ?
    I am understanding the brown-out means a under-voltage.

    Best regards,
    Masa
  • Hi Masa,

    I can't give you an exact voltage as this is not a guaranteed specification. There is some device to device and lot to lot variation as well as temperature variation but the FL_POR will be set when AVDD or DVDD go below (less than) the POR startup voltage of approximately 1.65V.  There is some hysteresis with respect to the actual voltage level.  The POR circuit of the ADS124S06 is much improved over the POR circuit for the ADS1248 family of devices.  However, operation below the specified minimum operating voltage of 2.7V does not mean the device will operate correctly at these levels even though the FL_POR flag is not set.  The FL_POR status flag when set is a direct indicator that the supply dropped below the POR startup threshold and the device has now reset.

    Best regards,
    Bob B

  • Hi Bob,
    Thank you very much for the answer. I understand.
    Masa