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DAC82002: Maximum achievable update rate of both channels

Tim Kostka
Prodigy 70 points
Part Number: DAC82002

Tool/software:

I'm using the DAC82002 and am interested in achieving the maximum update rate possible. It appears to be only ~780 ksps (or maybe 500 ksps) per channel rather than 1 Msps and I want to confirm.

Per the datasheet, the maximum SPI rate is 50 MHz. Each transaction is 24 bits. So to update DAC-A output, it takes 24 bits, and to update DACB output, it takes a separate transaction of 24 bits. Between transactions, the !SYNC line must be high for 160 ns.

So the minimum time required to update a single register is 24 bits at 50 MHz (480 ns) plus the required !SYNC idle high time (160 ns) for a total of 640 ns.

(0 ns): update DAC-A
(0.640 us) update DAC-B
(1.2 us) update DAC-A
(1.84 us) update DAC-B
etc...

Or, am I misinterpreting the datasheet and is t_DACWAIT the duration one must wait between any transaction, not just a per-channel wait. This would limit the update rate to 500 ksps per channel.

(0 us): update DAC-A
(1 us) update DAC-B
(2 us) update DAC-A
(3 us) update DAC-B
etc...
  • +1
    TI__Mastermind 33548 points

    Hi Tim, 

    Usually settling time is the dominant factor for update rate, which is 1us in the device, making the update rate 1MSPS. This is the update rate for the DAC. If you want to consider the channels separately, then yes, the update rate for each channel is 500kSPS because the DAC can only update one channel at a time. 

    The settling time happens to be the same as this 1us delay time, so the update rate is still going to be 1MSPS. If you are using an external buffer, you'll need to take the buffer settling time into account. 

    The 1us tDACWAIT is between any transaction (your second example). This comes from some internal circuitry requiring a delay before it is ready for another output update. 

    Best,

    Katlynne Jones

  • 0 in reply to Katlynne Jones
    Prodigy 70 points

    Katlynne,

    Thanks for the info, that checks out. Single channel can do 1 MSps, dual channels is 500 ksps, updated alternately.

    Understood about setting time being important.

    Regards,

    Tim