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DAC81408: TOGGLE pin VIL

lei zhou1
Prodigy 200 points
Part Number: DAC81408

Hi

        I have use DAC81408in my new design, TOGGLE0 is pulled up to 3.3V through a 10Kohm, the schematic is reference from DAC81408 EVM User's Guide， I think the 10K pull up resistor is used to enhance toggle input signal driving ability:

 

But through test, I found out net TOGGLE0 VIL=0.7V, after remove R178, TOGGLE0 VIL=0V, so the TOGGLE0 have about 2.69K pull down resistor inside of DAC81408? Can I remove R178 from PCBA BOM, the TOGGLE0 VIL=0.7V， exceeding my design expectations：

  

  • 0
    TI__Mastermind 27618 points

    Hi Lei, 

    Sanjay will review and provide a response. 

    Best,

    Katlynne Jones

  • 0 in reply to Katlynne Jones
    TI__Intellectual 2090 points

    Hi Lei,

    There is no internal pull-down on TOGGLE0 (and other TOGGLE pins) pins. If possible please check the TOGGLE0 (at 3.3V) pin input current, it will clear the doubt regarding the pull-down resistor. 


    a. Can you please send the full schematic from from the source digital drive to DAC51408 TOGGLE0 pin ?

    b. Also please make sure that there is no pull-down enabled from input source digital driver side.  
     

    Let me know if this helps or not. 

    Thanks,
    Sanjay
      

  • 0 in reply to Sanjay
    Prodigy 200 points

    Hi Sanjay, thank for you help. The  full schematic as below, TOGGLE0 source signal is from OSC1: SIT1534, if there is no internal pull down resistor on TOGGLE0, I think it may be SIT1534 sink current is very low cause the TOGGLE0 VIL≠0, the test point at OSC1.3 and TOGGLE0，the low level is 0.7V when R178 is installed, the low level is 0V when R178 is removed. So I want to remove R178 from BOM, is it OK? If not OK, is there any other way to solve this problem？

      

  • 0 in reply to lei zhou1
    TI__Intellectual 2090 points

    Hi Lei,


    Can you remove R315 and check the signal with R178 (installed)?

     

    And this still does not help, you can remove the R178, that will not have any impact on the TOGGLE0 functionality. 
     

    Regards,

    Sanjay