• State TI Thinks Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 579 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.

LM5066IEVM-626: Startup with load is not possible

user6504975
Prodigy 50 points
Part Number: LM5066IEVM-626
Other Parts Discussed in Thread: LM5066I

Dear Support,

LM5066IEVM-626 board was modified to our needs.( VIN=28V; Max. current = 3A) 

Modifications performed on the board:

  • Q3,R5,C5 were removed.
  • other components were replaced according to the attached calculation tool.

If load is applied to the output after S1 is ON, everything works as expected.

If load is applied to the output and S1 is turned ON afterwards, startup is not performed. LM5066I in the presented configuration is able to drive 0.6 A only. Above 0.6 A I receive over current fault, and the output is disabled.

In my application I need to supply a permanent load, which is always connected to the output of LM5066I. The load can not be enabled or disabled, it is switched on by the LM5066I output.

PLim is nearly double as the calculation tool suggests, due to the fact that load is available on startup. 

Could you provide some hints, in order to find the issue.

Thank you!

Best Regards,

Alpar

 LM5066I_Design_Calculator_REV_C-3A.XLSX

  • 0
    TI__Guru** 105811 points

    Hi Alpar,

    Welcome to E2E!

    What is the type of load and at what voltage the load turns-ON?

    Remove soft-start capacitor C1, set higher power limit such as 110W and test again.

    Please share start up test waveforms Vout, GATE, Timer, input current

    Best Regards, Rakesh

  • 0 in reply to Rakesh
    TI__Guru** 105811 points

    Hi Alpar,

    Any update ?

    Best Regards, Rakesh

  • 0 in reply to Rakesh
    Prodigy 50 points

    Hi Rakesh,

    Thank you for your support. Setting higher power limit solved the issue. 

    Could you provide information regarding maximum current sink capability of PGD and nSMBA pins?

    I do not find any information in the datasheet regarding pin current sink capability.

    It is only mentioned that during test conditions current sink was 2 mA on PGD and 3 mA in case of nSMBA.

    Is there an explanation why the LM5066IEVM-626 uses 100k pullup on PGD pin?

    In my design I would like to add LEDs to these lines without using any other external components.

    P5V and P5V_SW are the same power rails, P5V_SW is interrupted with a jumper.

    Thanks!

    Best regards,

    Alpar

  • 0 in reply to user6504975
    TI__Guru** 105811 points

    Hi Alpar,

    Good to know that.

    Usually customers prefer higher pullup resistor to reduce the shunt current. For the same reason, 100k was used on EVM. Please treat 10mA as maximum current sink capability of PGD and nSMBA pins.

    Best Regards, Rakesh