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DAC3161/ 71 Datasheet vs. EVM Pin Connections

Dale Lawson
Prodigy 60 points
Other Parts Discussed in Thread: DAC3161

Using a TI DAC3161 (or maybe 3171) in a new design. We noticed some discrepancies between the data sheet (SLAS959A) and the DAC31x1 EVM schematic (revision A, 17 Apr 2013):

 

1. Data sheet says pins 51-54, 63-64 are no connects that may be left open or grounded.

EVM schematic ties them to VDDA18.

 

2. Data sheet says VFuse (pin 8) should be tied to 1.8V digital supply (pins 21, 28).

EVM schematic ties it to VDDA18.

 

Need to know which are correct.

  • 0
    TI__Mastermind 46290 points

    Dale,

    DAC3161 is a high-speed product. I'll move this thread to the correct forum in just a moment.

  • 0 in reply to Kevin Duke
    TI__Mastermind 29220 points

    Hi,

    i have a question in to the design team for specifics on these pins. 

    Obviously it doesn't matter in this case.  But in general pins labeled as NC might really be completely unconnected (no bond wire) or they might be bonded to circuitry that is 'off'.  I dont know which that is for these pins, but i have asked.  Either way, connecting to supply would not present a problem and since the EVM connects these to supply then it is not a problem here.  But sometimes an NC pins might be for 'test' or future features.  (Should be labeled as reserved if that were the case.) On this device, pins 53-54 are the pins that the other channel output would be on the dual version of this device, so I am pretty sure these pins would not have a probelm with a supply connection.  But the otherNC pins I dont know about, but apparently there is also not a problem.  But i am checking.

    VFUSE is a pin we use in factory test, and after factory test it just needs to be conencted to supply.  It could be either the analog or digital supply, it doesnt matter.  The circuitry has already been programmed and is not going to be doing anything with the supply conenction.  But in general we want to make our EVMs follow exactly what the datasheet says so that we don't invite questions like this on apparent discrepancies and for that reason we should have made the EVM connect it to the digital supply.

    Regards,

    Richard P.

  • 0 in reply to Richard Prentice
    TI__Mastermind 29220 points

    Hi,

    Pins 51, 52, 62 and 63 are not bonded to anything; you should measure an open if you check those pins. In a preliminary datasheet these were going to be analog 1.8V, but there was an issue of potential coupling to the analog out so these pins were changed to no connects.  This is probably why the EVM was made with these pins connected to supply.

    But pins 53 and 54 are bonded to internal circuitry that is inactive.  Because of the ESD structures on these structures it is best to *not* connect these to supply.  As the datasheet says, open circuit or ground is correct.

    VFUSE can connect to either analog or digital supply, but digital supply is best.  Upon power up there can be some poewr draw from VFUSE as the fuse states are sensed, adn the VFUSE sensing is powered of the digital supply so it is best if both VFUSE and the fuse sensing are off the same supply.  But - no harm if VFUSE is connected to the analog supply.

    Regards,

    Richard P.