ADS1248: ADS1248 reaction caused by missing of SPI SLCK/DIN

Part Number: ADS1248

Dear Sir,

It is not a trouble but system error case study. A customer test ADS1248 reaction at a case when SCLK and DIN are missing during a normal operation.

What status ADS1248 will go into?

They actually test on their board (single ADS1248 communicating with MPU) and met that ADS1248 stopped interruption of conversion completion like sleep mode. Is it expected reaction?

And what is proper operation required to recover or reset the above situation in general?

 

Best regards,

Masa

5 Replies

  • Katayama-san,


    If the ADS1248 does not receive SCLK and DIN, the ADS1248 should not change status. The device should not receive a command.

    Case 1 (No SCLK): Even if DIN is being changed, the data is not clocked into the device without an SCLK.

    Case 2 (No DIN): If the DIN is unconnected, then it's likely that the device interprets the command, but again, it shouldn't change. An unconnected DIN that floats high looks like FFh, which would be a NOP. An unconnected DIN that floats low is interpreted as a WAKEUP command. This command only is used when the device is only already in a SLEEP mode.

    If the customer thinks the device goes into sleep mode after a disconnecting the SPI connection, I would re-establish the SPI and read the registers of the device and see if the device responds (if the device does respond, read the registers to see if they have changed). I would also check the external START and /RESET pins to see if they are still high. If there is an external clock, I would also check that. If there is way to measure the digital or analog supply current, the customer can check to see if they have changed when the SPI is disconnected. Supply currents will drop if the device is in power-down modes.


    Joseph Wu
  • In reply to Joseph Wu:

    Hi Joseph,

    Thank you very much for your advices.

    The customer checked as follows;
    1) check the external START and /RESET pins to see if they are still high.
    Both pins are fixed in hardware with
    RESET pin = high (tie to 5V VDD)
    /REST pin = low (tie to ground)

    2) an external clock
    Using internal clock

    3) measure the digital or analog supply current if they have changed when the SPI is disconnected
    Before the disconnection : about 1mA
    After the disconnection : 0.3 ~ 5mA (fluctuate every disconnect time)

    GPIO (set output to high) always became low at the disconnection.

    The disconnection is performed by mechanical switch on and off between SLCK and signal ground.
    One time disconnection did not cause so called sleep situation but several on-off switchings made the phenomenon.

    They are checking the result of re-establish the SPI and read the registers of the device.


    Best regards,
    Masa
  • In reply to Masa Katayama:

    Katayama-san,


    I don't know of anything except for valid commands that can change the status or configuration of the device by toggling the SCLK or DIN.

    As I mentioned in the previous post, if the device does change (with different current or GPIO setting) I would reread the registers of the device to see if they have changed. If there is a change in the current, they should also record the value and see if it corresponds to a value that indicates a change in the PGA gain, or different setting in the device. However, I don't know of any setting in the device that would create a 5mA current


    Joseph Wu
  • In reply to Joseph Wu:

    Hi Joseph,
    Thank you very much for your response. I had a typo in my previous thread.
    Both START and /RESET pins are connected directly DVDD(5V) without resistance.
    Is it okay?

    and I will inform you as soon as I got register values to be read,

    Best regards,
    Masa
  • In reply to Masa Katayama:

    Katayama-san,


    I'm sorry, but I thought I had already responded to your last post. By yes, that should be ok. I had already understood because if either were low, the device would not respond to the full set of commands.

    One other thing that I wanted to mention, is that they should monitor the voltages of the pins as well as the supply. If there are any overvoltages because the device supply is pulled to high it may damage the device. If there are any undervoltages it may cause the device to reset. Any additional capacitance or inductance in the leads can cause some spiking.

    Let me know if your customer returns with any questions. Again, sorry about the delay.


    Joseph Wu