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ADC3421: Power-down modes

Yosuf Taraki
Prodigy 60 points
Part Number: ADC3421

Tool/software:

I would like to better understand the various power-down modes of operation for the ADC3421.  Register 15h has bits assigned for powering down individual channels (A, B, C, D).  There is also a STANDBY bit and a Global Power-down bit. 

What is the difference between these modes? 

How is Global Power-down different from powering down channels A, B, C, and D?

How do we exit the Global Power-down mode?

  • 0
    TI__Prodigy 110 points


    Using SPI write commands, writing 1 to the GLOBAL PDN register field should result in all the channels A,B,C,D being powered down at the same time.

    Writing 1 to the CHA PDN register field will result in only channel A being powered down, and so on.
    This is used when only wanting to power down 1 or 2 channels at a time for example.

    To exit the global power down, simply write 0 to the GLOBAL PDN field, and all channels shoul continue normal operation, thus exiting the global powerdown mode.

    the config pdn pin register field is used to program the physical PDN pin on the device into either a global PDN pin or a standby pin.

    Does this answer your question?

  • 0 in reply to Joseph Ferri
    Prodigy 60 points

    Thank you for the information.  I understand that individual channels can be placed in power-down mode by setting the corresponding PDN bits in register 15h, and that all channels can be powered down by setting the global PDN bit in register 15h.  However, I have also found that setting the PDN bits for all 4 channels (A, B, C, and D) is not exactly the same as setting the global PDN bit.  There is some difference in behavior.  Setting the global PDN bit results in some sort of lock-up in our system, whereas setting the 4 individual PDN bits does not.  What is the difference between setting all 4 PDN bits and setting the global PDN bit?

    According to my understanding, the power-down mode on all channels is removed if the software RESET bit of register 06h is set.  Is this correct?

    I am not sure of the difference between STANDBY and PDN.  Does setting the STANDBY bit of register 15h put all 4 channels in Standby mode?

    Thanks for your help.

  • 0 in reply to Yosuf Taraki
    TI__Mastermind 24530 points

    Hi Yosuf,

    See my answers/comments below: 

    What is the difference between setting all 4 PDN bits and setting the global PDN bit? RR: The difference is the global PDN will power down the entire device, where if you only power down the channels individually, the digital link will still be up and running. You can probe the FCLK pins with an oscope to verify.

    According to my understanding, the power-down mode on all channels is removed if the software RESET bit of register 06h is set.  Is this correct? RR: yes, this is correct.

    I am not sure of the difference between STANDBY and PDN.  Does setting the STANDBY bit of register 15h put all 4 channels in Standby mode? RR: in standby mode, this only powers down some of the device so you can wake up the device faster from this state. For example, most times the internal voltage reference will remain on in standby mode, as this sets up all the internal bias levels within the device design internally.

    Regards,

    Rob

  • 0 in reply to Yosuf Taraki
    TI__Mastermind 20135 points

    Yosuf,

    There are a few things to note here.

    The individual powerdown will powerdown the analog circuitry internal to the ADC specific to that input channel. This is useful if your system only needs a reduced number of channels at any given time, you can simply power off the unused channels. 

    The standby and global power down are both means to disable/turn off the ADC to different states with a single command. The standby will place the ADC in a semi-powered down state (power consumption decreases to 45mW). The global powerdown will fully powerdown the ADC (power consumption drops to 5mW).

    To exit global powerdown, you can write to the SPI register to turn it off and the ADC should return to its previous state. Sure, you can use RESET to exit the powerdown as the full register map of the device is reset to the Reset value shown in the datasheet, which will have the global powerdown disabled, ie the device will function. When you use RESET, every register will be reset so if there are anyregisters which you modified they will need to be rewritten.

    The standby leaves the ADC running while powering down all additional features/circutis which is why it burns more power than full global powerdown. Exit global powerdown takes 85us while standby only takes 35us, this is the only difference as far as I know between the two (standby and global powerdown). Writing the 4 channels to powerdown and then writing either standby or global pdn will not reduce power consumption further since both standby and global pdn will powerdown the 4 channels.

    Thanks, Chase