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TPS7A80: Output voltage drifts

Danilo A.
Mastermind 24705 points
Part Number: TPS7A80

Hi Team,

Our customer used the TPS7A8001 in a manner shown in this training video: https://training.ti.com/voltage-regulator-margining-precision-dacs . According to our customer,

Importantly, I need the output of the LDO to be controlled from 0 V to 1.8 V, and I typically have the output of the LDO set to 0.5 V. I followed the design instructions in the above link, and set R1 to 13000 ohms, R2 to 7500 ohms, and R1 to 12400 ohms. I have confirmed that the voltage coming from the DAC is stable. I have also placed a 1kOhm resistor, two 10uF capacitors, and one 1nF capacitor load at the LDO output. The setup is placed in a climate controlled room.

The issue I am facing is that the output voltage drifts, on the order of 2-4 mV over an hour long period. Is there any way to make the output stable?

Regards,

Danilo

  • 0
    TI__Mastermind 37965 points

    Hi Danilo,

    Are they using an ADC as feedback for the DAC? If the ADC/DAC have sufficient resolution then this drift can be eliminated but if they do not then there's not a whole lot that can be done. One thing they can try is to let the LDO run for a period of time (burn in) and the LDO output should settle and should not drift further. 

    Regards,

    Nick

  • 0 in reply to Nick Butts
    TI__Mastermind 24705 points

    Hi Nick,

    Our customer shared the schematic diagram and it seems there is no ADC in his application. According to our customer,

    Does TI have any reference literature or application notes on using this feedback? I have some idea of what it would look like, but I would like to make sure I am doing it properly.

    We have tried running it for several hours and while the drift does slow down considerably after about 30 mins, it is still noticeable. For an output of 0.5V, it will drift noticeably, on the order of 10 mV after leaving it running all night.

    Regards,

    Danilo

  • 0 in reply to Danilo A.
    TI__Mastermind 37965 points

    Hi Danilo,

    We don't have any documentation for this ADC feedback, but it is a simple feedback scheme where the ADC samples the output and the DAC output is changed until the output is within an acceptable range. 

    Our long-term drift data for our LDOs is relatively limited, but what we have seen is that drift can take on the order of hundreds of hours to settle out. Drift is normally not considered problematic because the output still stays within specification after drifting. Without doing a burn in or without some sort of additional feedback there is no easy solution to eliminate drift, especially if about 2-4mV drift is considered too much for an application. So, I think the ADC/DAC feedback you are after here is the best way to achieve higher precision. 

    Regards,

    Nick

  • 0 in reply to Nick Butts
    TI__Mastermind 24705 points

    Hi Nick,

    Your answer resolved our customer's inquiry. Thank you very much for your support!

    Regards,

    Danilo