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DAC8740H: Pressure Transmitter Schematic Design

Part Number: DAC8740H
Other Parts Discussed in Thread: DAC161S997,

Hello All

I have designed schematic of isolated pressure transmitter with HART feature. Kindly please check and suggest whether it is OK or not.

Nakul Audeechya

9817.pdf9818.pdf

  • Nakul,

    I only have a few comments for you on this schematic. I've concentrated on mostly the DAC8740H and the DAC161S997 in this schematic.

    For the cap on MOD_IN, 100nF for C10 seems high to me, and I would just recommend the same value as we use in the example schematic in the datasheet of 2200pF. Also on the MOD_OUT pin, you have C8 set to 220nF which is very high. The datasheet specifies a range for the MOD_OUT of 5nF to 22nF. However, it's best not to use the maximum because parasitic capacitance would increase the value even more. The MOD_OUT pin may have problems driving above 22nF of capacitance.

    For the pull-up on ERRB for the DAC161S997, I think a 1MΩ resistor for R8 would be rather slow. I'd probably use a 10kΩ resistor.

    What models of ferrites are you using for L3 and L4 for the power in the DAC161S997?


    Joseph Wu

  • Hi Joseph

    Thank you for carefully look in my circuit.

    I have used Ferrite Bead, 1000 ohm @ 100 MHz, 0.25 A 0402 for L3,L4  and Ferrite Bead, 600 ohm @ 100 MHz, 1.5 A, 1206 for L1, L2. 

    What do you think about C9 and C17? Because C8 is already in the same path.

    Nakul

  • Nakul,

    I need to check something on this one. I'll get back to you soon.

    Joseph Wu

  • Nakul,

    The ferrites should be fine in your circuit.

    For the C8, C9, and C17, I generally will go by the capacitors outlined in the EVMs. For C9 and C17, I would leave them as 6800pF and 0.22uF as in the DAC161S977EVM. For C8, earlier, I had recommended reducing it and I would still do that, but I don't think the capacitor is strictly necessary. I would still reduce it and leave it as uninstalled.

    Joseph Wu