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DAC60508: DIV/GAIN-Setting of 1/1 "not recommended", but default in DACx0508Z?

Christoph Berger
Prodigy 20 points
Part Number: DAC60508

Hello, 

I'll likely be using a DAC60508 in an upcoming project and while browsing the datasheet I came upon the following quirk (?): 

  • page 22: 8.3.1.2 Output Amplifiers: Table 1 says that setting both DIV and GAIN to 1 is "Not recommended"
  • page 21: 8.3.1.1 DAC Transfer Function: regarding eq. 1 it says that DIV is "Set to 1 by default." and GAIN is also "Set to 1 by default in DACx0508Z"

So the default state of the DACx0508Z seems to be a "Not recommended" state. What can I expect the DAC to output in this case until I set the DIV/GAIN-registers to a more suitable state (i. e., DIV by 2, GAIN of 2 for 0V..2V5 range in my case)? What is the nature of this "not recommended" state? I initially assumed this would be the state that's least likely to behave oddly. 

Thank you very much in advance!

Christoph

  • 0
    TI__Guru 52683 points

    Hi Christoph,

    I believe we were a little terse when we stated that it was 'not recommended'.  Really we should say that it is not recommended under certain power supply configurations.   The internal reference is typically 2.5V.  So if we look at the recommend configuration table:

    Basically, what we are trying to convey is that the reference should be divided if your supply is lower than 5V.  The switches in the DAC resistor ladder require some minimum supply headroom to operate.  So if you have a lower supply, you require a lower reference voltage.  

    For example, note that in the recommended operating conditions we show that with a 2.7V supply the reference can be at most (VDD-0.2)/2 or 1.25V if the divider is disabled.  If the divider is enabled, then we can have a reference input of 2.5V.  

    So there is some debate if having the resistor divider disabled by default is the best configuration, but it is safe if the VDD supply is 5V to 5.5V.

    I will also convey to the team that we should expand this explanation if we revise the PDS.

    thanks,

    Paul