• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 64 subscribers
  • Views 1158 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

UCC28950: UCC28950 constant current output schematic check

Rock Su
Intellectual 2220 points
Part Number: UCC28950
Other Parts Discussed in Thread: UCC28951, LM324

Dear colleague,

The technical requirement of the project customer is working on with UCC28950 is current limiting output.

That is, constant current output after the output exceeds 25A.

Now they have built a schematic of the circuit, and the idea is to use the current signal, compare it with the reference voltage, and adjust the COMP terminal. Please check whether this is feasible. The circuit diagram is as below, and the parameters are not determined.

Thank you very much!

B.R.

Rock Su

  • 0
    TI__Mastermind 25570 points

    Hello Rock

    Texas Instruments does not recommend that the COMP pin of the UCC28950 (or UCC28951) be used as an input. In the customer schematic the LM324 IC is being used to drive the COMP pin as an input so we cannot recommend this approach.

    The usual way to implement a CI/CV characteristic is to use two external error amplifiers and to configure the on-board error amplifier of the UCC28950 as a voltage follower. This is described in the attached note. /cfs-file/__key/communityserver-discussions-components-files/196/CI_5F00_CV-Characteristic.docx

    The article mentions the UCC28951 but the UCC28950 will behave in the same way.

    The note contains some links to reference designs using this approach.

    Another way to do this is to vary the EA+ reference input to the error amplifier. A diode coupled amplifier like the LM324 could do this - D3 would connect to the junction of R33 and R44. In current limit, the LM324 will pull down the reference to the error amplifier and this will reduce Vout. I don't really like this idea because you do not have independent control of the CI and CV loop bandwidths

    I would prefer the first approach because you can guarantee that you can control the output current right down to 0V on the output. The CI and CV loop compensation is independent - and it has been proven to work.

    I'd be happy to review their updated schematic.


    Regards
    Colin

  • 0 in reply to Colin Gillmor
    TI__Intellectual 2220 points
    Dear Colin,

    Thanks a lot!
    Customer are studying your reply.
    I will updated schematic later.