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DAC8580 digital filter again

Georgi Georgiev1
Prodigy 20 points
Other Parts Discussed in Thread: DAC8580

Hi.
i'm trying to make digital filter work but whithout success so far.
I have read the previous post on this subject and i don't find it to be very helpful.


"BPB should be set low with RSTB and MUTEB tied high." is a sentence which means:


BPB = 0
RST = 1
MUTEB=1

OR

BPB = 0
RST = 0
MUTEB=1 ?

To which row(combination of logic states on digital inputs) of table 2 this refers.

What about some timings? Is it realy possible to reset this digital filter?  
Any help will be appreciated.

  • 0
    TI__Mastermind 46290 points

    Georgi,

    I miss-typed my response there and have gone back to the original post and corrected it. Sorry for the confusion. Let me break down the sequence here.

    At power up all of the digital inputs should be connected to logic low. Once the power up sequence has been completed we can begin to manipulate the digital inputs, and the first thing you're probably going to do for any mode of operation is bring MUTEB high. At this point we're in the standard DAC mode of operation.

    To enable the digital filter you need to first configure the OSR1 and OSR2 pins as desired while RSTB is tied low. Once the OSR pins are set bring RSTB high and the filter will become active. Note that right now the digital filter is active but since BPB is still tied low we don't see the digital filter values at the output. BPB can be brought high before, during, or after configuration of the OSR1, OSR2, and RSTB pins - for the item labeled 'filter initialization' in table 2 BPB should really be 'dont care'. The sequence doesn't matter, the filter is purely gated by the state of the RSTB pin and BPB just sets which source is controlling the output (either the digital filter or the DAC data register).

    If the digital filter settings are changed while the filter is active the filter will become unstable. To recover from this filter instability toggle the RSTB pin and the filter should re-initialize with the new OSR settings.

    Are you testing the DAC8580 on a DAC8581EVM?

  • 0 in reply to Kevin Duke
    Prodigy 20 points

        Kevin i must thank you for this message.  Meanwhile i managed to make this filter to work. The
    problem was that the serial communication mode was incorrect. The chip is mounted on small
    prototype board and was connected to device that uses another type of serial DAC, in order to
    conduct some tests with DAC8580. When i correct the serial mode as is required, the filter
    starts every time. All the digital inputs have pull-down resistors  and this is all(for now) -
    no dedicated startup circuitry.

    Anyway thanks again - i think your answer will be on great use.