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TLV5632 Output Load

JoeY_937
Prodigy 70 points
Other Parts Discussed in Thread: TLV5632

Hello - I have a question regarding the recommended output load of the TLV5632. The datasheet calls out a maximum capacitance of 100pF and a minimum resistance of 2kohm. Could the part be damaged if the loading capacitance is on the order of 200pF to 10nF? I'm seeing a couple of our boards that use this DAC become either completely inoperable or the output offset and amplitude is completely different than what is being commanded through the SPI bus. Is it recommended to use a low capacitance input amplifier to act as a output buffer for this part? Thank you.

  • 0
    TI__Genius 10615 points

    Hi JoeY,

    The maximum capacitance is set in order to prevent oscillations at the output. The DAC has an internal buffer that can go unstable if the 100 pF is exceeded. Usually it is a conservative estimate, so even 200 pF might still be okay. The settling time will be heavily affected. 10 nF is definitely too much, you might not see oscillations at this point because the system will be heavily over damped, but you can expect the settling time to be several orders of magnitude.

    However, I would not expect the part to be damaged by loading a large cap at the output.

    • Do you still see the same behavior after removing the large cap?
    • Is there anything else acting as a load on the DAC?
    • How are you measuring the output? How long do you all for it to settle before measuring?

    If you want to see some solutions to driving heavy loads, you can take a look at this TI Design: Bipolar +/-10V Output from a Unipolar DAC for Industrial Voltage Drivers.

    The document is written such that you can modify it to suit your needs.

  • 0
    Prodigy 70 points
    Thank you Eugenio for your response. We haven't seen oscillations at the output of the DACs, only that we have seen one case where one of the output channels was completely inoperable, and another case where three of the output channels had a higher offset and lower amplitude than what our controller was commanding through the SPI bus. In each case, I replaced the DACs and the issue went away. To answer your question regarding "Is there anything else acting as a load on the DAC" - the DAC drives into a high pass and low pass passive filter, but then there is a negative feedback amplifier connected past these filters. I plan on monitoring the output of the DACs more closely with a scope and test out different use cases (start/stop/shift in drive strength) to see if any voltages that could be damaging would appear on the DAC outputs.