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DAC161S997EVM TESTING WITH HART signalling

sruthi uk
Prodigy 120 points
Other Parts Discussed in Thread: DAC161S997EVM, DAC161S997

Hi all,

I tried to tested the DAC161S997EVM board for getting 4-20mA current loop along with the HART modem AD5700 interface. Using the GUI softwre the DAC current is kept to be constant according to  values set in DACCODE register.Then without removing the output capacitors of DAC161S997 , the HART data having UART format  transmitted through HART modem (HART_OUT) is given to the C3 input capacitor of DACEVM board and from the LOOP+1 it  is taken back to the ADC_IN of HART modem . But there is no HART FSK signal is coming out from the DAC161S997EVM board .What may be the reason for this???

With regards,

sruthy uk

  • 0
    TI__Genius 16890 points
    Hello Sruthy,

    When using the DAC161S997 eval board the HART signal should should be input to the connector labeled HART_TX1. This connects the HART signal through a capacitor to the C2 pin. It should not go to the C3 pin as you mention in your post. The HART signal can be seen at the HART_RX1 connector.

    Mike
  • 0 in reply to Michael Stout
    Prodigy 120 points

    Hi,

    what is the purpose of  capacitor c22 in this dac evaluation board?.HART signal given to testpoint H9 is observed in HART_TX connector pins and also in pin2 of HART_TX wth respect to test point COM2.  HART_OUT from dac is only observed in the HART_RX connector while no signal is coming when it is taken between pin2 of HART_RX and testpoint COM2. What is the reason behind this??

    sruthy uk

  • 0 in reply to sruthi uk
    TI__Genius 16890 points
    Hi Sruthy,

    C22 is to set a common reference point for the HART TX and RX chip. The TX of the HART chip connects to the HART_TX1 header and the RX connects to the HART_RX1 header. The common pin of each of these headers is connected and then the capacitor sets them as a common reference that is different than the board.
    Something I noted as I was looking at the schematic of the user guide is that C1 and C3 are mislabeled. C1 is pin 14 and C3 is pin 12. This also means that the capacitors mounted on the PCB (C17 and C20) need to be switched. The pin assignments and component values as shown in the datasheet are correct.

    Mike