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DAC60508: Isolation resistor value at the output

Shinichi Inoue
Guru 19701 points
Part Number: DAC60508

Dear Specialists,

My customer is considering DAC60508 and has a question.

I would be grateful if you could advise.

---

DAC60508 is used as the bias voltage of analog IC. See the circuit diagram below.

The DAC output voltage is set to a fixed voltage without changing the DAC output voltage after setting the voltage at power-on.

Since the DAC output is directly connected to the bias terminal of the analog IC, a capacitor is inserted for stabilization.

As a countermeasure for the capacitor, a 10 Ω resistor is currently inserted to prevent oscillation of the DAC operational amplifier output.

In the circuit configuration below, 10Ω is used as a countermeasure for oscillation of the DAC operational amplifier output, is there any problem

If there is a recommended value, could you tell me the value?

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I appreciate your great help in advance.

Best regards,

Shinichi

  • 0
    TI__Mastermind 18546 points

    Hi Shinichi,

    Since you have isolated capacitor from the output buffer with series resistor, I don't see any issues. I ran a quick simulation to check this configuration is stable or not. 

    This will work perfectly fine. One concern though is the voltage drop across 10 ohms resistor when you are drawing 10mA current. If your device can tolerate 100mV difference in supply, I don't see any issues.

    Also please make sure that you have adequate headroom for the power supply for DAC since you are drawing 10mA, we need min 300mV

    Hope this helps.

    Regards,

    AK

  • 0 in reply to Akhilesh K
    Guru 19701 points

    Hi AK,

    Thank you for your quick reply.

    I understand 10ohm resisutor is no problem and pay attention for the headroom.

    I'll share these information with the customer.

    I appreciate your great help and cooperation.

    Best regards,

    Shinichi

  • 0 in reply to Shinichi Inoue
    Guru 19701 points

    Hi AK,

    The customer has an additional question.

    Could you please advise.

    ---

    I understand 10ohm is no problem.

    In addition, how low can the resistance value be?

    If possible, I want to set it to 0Ω.

    ---

    I appreciate your great help and cooperation.

    Best regards,

    Shinichi

  • 0 in reply to Shinichi Inoue
    TI__Guru 52683 points

    Hi Shinichi,

    Using 0Ω will likely just result in the device oscillating again.  I do not have a stability model for this device, but I suspect you could reduce the resistance on OUT2 to 2Ω to 5Ω.  This is because the 10µF load is probably going to critically dampen the output.  OUT1 only has 100nF, so I recommend 5Ω to 10Ω.

    Thanks,

    Paul

  • 0 in reply to Paul_Frost
    Guru 19701 points

    Hi Paul,

    Thank you for your reply.

    Yes, 0ohm is not recommended because OUTx is amplifier output.

    I'll share your suggested value with the customer.

    I appreciate your great help and cooperation.

    Best regards,

    Shinichi