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DAC8564, DAC8562 and DAC7564 - unable to output < 1 mV

Stefan Drechsel
Prodigy 20 points
Other Parts Discussed in Thread: DAC8564, DAC8562, DAC7564, LM7705

Dear all,

we use DAC8564, DAC8562 and DAC7564 in several configuration:

-  with external Reference LM41440 1.024 V or internal reference and Vref_L to GND

-  IOVDD and AVDD 3,3 V with recommended filter

There is no way to output voltages below approx. 1 mV when input is 0x0000h. The specific value depends on measured channel and DAC. Same happens after power-on without any connection to microcontroller or additional components. For example with DAC8564IBPW there is no useful output below 0x51h.These value seems much higher than given in datasheets.

For ongoing projects, we search for DAC with similar performance but "more rail-to-rail" functionality (e.g. 0.1 mV when using internal reference)..

Any idea will help.

Kind regards,

Stefan

  • 0
    TI__Mastermind 46290 points

    Hi Stefan,

    The problem is that the output amplifiers in the DAC need some headroom from their rails. 1mV from the negative rail is actually pretty good, operational amplifiers that just get within 100mV of their supply rails are frequently marketed as "rail-to-rail" devices.

    I have not built and tested this solution yet, but one possible work-around would be to bias the DACs GND pin to a negative voltage and then connect VREFL to the board GND. The device doesn't feature a DGND pin, so keep in mind that IOVDD would still be referred to the negatively biased GND pin.

    The LM7705 is a new device from TI that is targeted at such applications.