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ADS1243-HT : (1) About # of bit and resolution (2) The PDWN input

Yuquan Li1
Intellectual 460 points
Other Parts Discussed in Thread: ADS1243-HT

Hello:

For ADS1243-HT

(1) The data sheet says the effective resolution is a function of Gain setting with an effective resolution of 19 bits at gain of 128.

      This means at gain of 128, only the Most significant 19 bits are effective, the remaining 5 bits means nothing. Is that right?

      If we program the gain to be 8, what is the effective resolution ( # of effective  bits)?

(2) The PDWN input: The data sheet says: Active low, power down all digital and analog circuit

    My understanding is that, after pull the PDWN low, all the info written to the chip is gone. Next time when we pull it high, we need to redo channel selection setting... ect.

  Is this right?

Thanks


Y.L

  • 0
    TI__Guru** 113765 points

    Yuquan,

    You will always receive a 24 bit response from the ADC, but depending on data rate, buffer on/off and PGA setting you will have different noise.  Noise can be characterized peak to peak or RMS.  For the effective number of bits (ENOB) see the graphs on page 12 of the ADS1243-HT datasheet.  ENOB is generally characterized with noise RMS.  There are three graphs depending on reference voltage, and whether buffer is enabled or disabled for the different PGA settings and data rates.  Depending on the source of the noise, you can improve ENOB by averaging.

    It is not clear to me either if power down resets the registers.  Usually this is not the case.  In most of our devices, the state of the register contents are maintained.  You can experiment with this yourself by writing to the registers, placing the device in power down, bring it out of power down and then read the register contents.

    You can also issue the SLEEP and WAKEUP commands as well.  This will not erase the register contents.

    Best regards,
    Bob B