• State
  • Locked Locked
  • Replies 4 replies
  • Subscribers 66 subscribers
  • Views 1066 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

UCC27611 - LDO drop

Mohamed Ahmed27
Prodigy 30 points
Other Parts Discussed in Thread: UCC27611

Hi ,

I am using  2 x UCC27611 to drive 16 Low voltage SRs with a total current of 97 mA, i noticed that the drop across the internal LDO is around 1V at this current, i.e the input voltage to the driver Vdd=5.4V   and the reference voltage  Vref=4.4V, this has around 0.1W is this the normal with this driver as the LDO currently consumes 20% of the total driving power i have.

  • 0
    TI__Intellectual 2910 points
    Hi Mohamed,

    The VREF voltage you are measuring appears low. I will look into this. In the meantime, I have a couple of questions that will help diagnose the behavior you are observing:

    1. What value(s) of capacitors are connected to the VDD and VREF pins? A 0.1-μF ceramic capacitor located as close as possible to
    the VDD to GND in addition to a larger capacitor (such as 1-μF) is recommended. The VREF bypass capacitor should be sized to supply the turn-on surge current and located close to the VREF and GND pins.
    2. Is VREF at 4.4dc, or can you see an AC/switching component if probed with an oscilloscope?

    Regarding the power consumption, how are you measuring the 97mA?

    Regards,

    - Daniel
  • 0 in reply to Daniel Ruiz
    Prodigy 30 points

    Hi Daniel

    1- previously i was connecting a large 10uF between the VDD and gnd, now i changed to 0.1uF with a 1uF capacitor both  of them very close to the IC but still i can see a large drop between the VDD and Vref , for the REF voltage capacitor i use a 10 uF-10V capacitor

    2- the Vref is 4.4 with very small ripples at the switching instants

    i am using an ammeter connected in series with the power supply to measure the current

  • 0
    TI__Prodigy 645 points

    Hi Mohamed,

     Is the 97 mA current consumed in one driver? If so, that is well over the short-circuit current of the LDO (datasheet typ of 75 mA) and would cause the LDO to fail to keep the output regulated. If the 97mA is split between the two drivers, does it split equally?

    Regards,

    Nathan

  • 0 in reply to Nathan Schemm
    TI__Guru**** 189401 points
    Hi, Mohamed,

    I was just following up. Did you get the issue resolved?