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ADS1120: Behavior of ADS1120

Guru 16770 points
Part Number: ADS1120

Hi

We have question of ADS1120.

1.
We obtained the following waveform.


Accroding to the datasheet, the PSW would automatically close when the START/SYNC command is sent.


However, PSW seems to close without sending START/SYNC command in the following.
Is this behavior strange?

2.

After power-up, ADS1120 is set to single-shot mode and then do a single conversion.
Does this device enter the power-down mode after a single conversion automatically?
We have to save power consumption with a single data conversion.

BestRegards

  • Hi na na 78,

    There is a note within the bottom paragraph on page 33 of the most recent ADS1120 datasheet that states:

    "Note that writing to any configuration register wakes up the device as well, but only starts a single conversion regardless of the selected conversion mode (CM)."

    This means for question (1) that because the device internals restart the conversion automatically when the registers are written that the low-side switch will close automatically.  This is normal behavior.  You will need to issue a POWERDOWN command to open the switch between single-shot conversions. 

    For question (2), when the ADS1120 powers up initially, the device will always take one conversion then power down automatically.

    Best regards,
    Bob B

  • Hi Bob

    Thank you for your reply.

    I could understand the low-side switch would close automatically when the configuration register was written.

    So, should we send START/SYNC commend after register configuration?
    I'm referring the following thread.
    e2e.ti.com/.../2097952

    If sending START/SYNC is option in this case, I would not send this command to reduce execution time.

    >For question (2), when the ADS1120 powers up initially, the device will always take one conversion then power down automatically.
    The ADS1120 seems not to enter power down mode automatically after one conversion because I see the low side switch is not open.

    So, I could not get the following part of your answer;
    ... "the device will always take one conversion then power down automatically".

    What is the meaning of "power down automatically"?

    BestRegards
  • Hi na na78,

    Perhaps I misunderstood your original question.  Let me clarify.  When the ADS1120 initially powers up (first time power is applied to the device) the ADS1120 will take one conversion then power down.  However, if you change the configuration of the device by changing the register settings the device will power up (or stay powered up depending on when you write to the device) for one conversion and then power back down the device unless you set the PSW bit to '1' or if you turn on the IDAC current.  If the PSW is '1' or if the IDAC current is turned on, the ADS1120 will only partially power down.  To completely power down the ADS1120 to include opening the low-side switch and/or turning off the IDAC current, the POWERDOWN command must be issued.  To fully restart the ADS1120, the START/SYNC command must be issued.

    For your setup, you must issue the POWERDOWN command after writing the configuration to set the PSW bit to '1' to open the low-side switch.  To close the switch again you must issue the START/SYNC command.  So neither the POWERDOWN or START/SYNC commands are optional if you want to control the action of the low-side switch.

    Best regards,

    Bob B