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UCC2802 - External Reference?

Jeff Graham
Prodigy 20 points
Other Parts Discussed in Thread: UCC2802

Hi, Is it possible to use an external 5V reference on the Vref pin on the UCC2802? If so how much current should it be able to drive?

Thanks - Jeff

  • 0
    TI__Genius 9130 points
    Jeff

    On the datasheet recommended operating conditions, the max current out of the REF pin is rated at 5 mA. Similarly, in the electircal tables, the REF short-ciruit output current is worst-case min of 5 mA.

    So basically, yes you can add external load to the REF pin, as long as the total load is limited to under 5 mA.

    Thanks,
    Bernard
  • 0 in reply to Bernard Keogh
    Prodigy 20 points

    Thanks for the reply Bernard. I must not have stated my problem correctly. I want to use a higher precision external 5V reference and inject into the UCC2802 Vref pin.

    Jeff

  • 0 in reply to Jeff Graham
    TI__Genius 9130 points
    Jeff

    Here is the response I got from the IC design team, see below. Basically, we don't recommend forcing the REF pin externally, it probably won't work too well, and may not improve the effective accuracy.

    "Chances are that pulling REF high a bit is OK – there is no real sink capability I am sure – just a few mA of internal loading. I believe that pulling REF low is a problem, high current is one, also there is a UVLO threshold on REF that may come into play.

    I am going to guess that pulling REF to ~5.5V may be OK and the REF/2 level at the E/A will track – but there is likely 1-2% of random error between REF and REF/2. So the desired increase in precision may be elusive. Other parameters will also shift if REF is changed."


    Are you looking to improve the REF accuracy for the internal error amp? If so, then you could use an external VREF and external error amp, connect the FB pin to GND, and then use the external error-amp output to force the COMP pin to the required level for regulation.


    I hope this helps answer your query. If so, please click the "verfiy answer" button.

    Thanks,
    Bernard