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ADS1298 !PWDN vs. SPI STANDBY (PINS vs. SPI COMMANDS)

Tomasz Cedro
Prodigy 120 points
Other Parts Discussed in Thread: ADS1298

Hello! :-)

There goes another smart question on ADS1298 interfacing, the digital part this time :-) I am wondering if the SPI STANDBY/WAKEUP command is equivalent to using !PWDN pin so I can pull !PWDN and !RESET permanently high to save some BGA pins? As BGA seems to be best suited for mobile applications it would be nice to know what is the best way to save power. The more general form of this question is :are spi commands fully equivalent to dedicated pin control?

The documentation (SBAS459H – JANUARY 2010 – REVISED MAY 2011) says that "!PWDN (..) When PWDN is pulled low, all on-chip circuitry is powered down." (page 33) while "STANDBY (..) All parts of the circuit are shut down except for the reference section." (page 40). This sounds like these operations are not equivalent as the !PWDN pin also shuts down the SPI interface..?

Best regards from Poland :-)

Tomek Cedro

  • 0
    TI__Guru**** 180931 points

    **TI EDIT February 20th 2019; FOR GENERAL ADS129x ASSISTANCE, PLEASE SEE NEW BIOPOTENTIAL FAQ LOCATED HERE**

    Hi Tomek,

    Working late on a Sunday evening I see...  Standby and power down are not exactly the same thing in the ADS1298.  Please take a look at page 7 under the Power Dissipation section.  In standby mode, you draw typically 2mW of power versus 10uW in power down mode.  For this case, the PDWN pin is necessary to go into deep power savings mode.  Coming out of PWDN then will require 'wait' time until the reference and oscillator stabilize (refer to the flow chart on page 78). 

    The SPI RESET command is functionally equivalent to the RESET pin - for this you can simply tie the pin high.