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LM5170-Q1: Question about LM5170-Q1 EVM

Oliver Lin
Expert 3255 points
Part Number: LM5170-Q1
Other Parts Discussed in Thread: LM5171

Hi team,

My customer has two questions about LM5170-Q1 EVM.

1. User guide mentioned, under buck mode, need to turn on starting from HV-PS -> LV-PS and then LV E-load.  May I know what's the reason why connecting LV-PS? Since buck mode should be coming from HV-PS. Also another thing mentioned in the user guide in figure3., if the output voltage loop is closed, the LV-PS can be disconnected in buck mode operation, what does output voltage loop mean?

2. Also customer running actual testing, customer didn't turn on LV-PS, but other setting same as userguide, (HV-PS -> LV-E-Load -> Apply Master Enable -> Apply an analog voltage gradually rising from 0V to 1.5V at ISETA) But LV output only has 8V(full load). Once the load becomes 1A, the LV output has rised up over 20V, not regulating at 12V, is this behavior expected?

  • 0
    TI__Genius 12545 points

    Hi Oliver,

    If you only test buck mode, you only need a HV-PS and an E-load. 

    Install 50kohm at R4. Follow below jumper settings. This is the Constant Voltage configuration. 

    Set the E-load to CC mode. The output voltage is 14.5V.

     

    If you install jumper J36, that means output voltage loop is closed.

    If you do not install J36, it will be in Constant Current mode. The output voltage will be determined by the load. At light load, the voltage will increase till OVP is triggered.

    Best Regards,

    Feng

  • 0 in reply to Feng Ji
    TI__Genius 12545 points

    Hi Oliver,

    Please consider LM5171 if this is a new design.

    Best Regards,

    Feng

  • 0 in reply to Feng Ji
    Prodigy 10 points

    Thanks for your reply.
    I have a further question.

    Install 50kohm at R4. --> Is R6 also required to be installed?

    (Since I looked through datasheet and user guide and found that the applied voltage of UVLO should be in range of 2.5-6V:

       UVLO: The master enable command. Apply a voltage > 2.5 V and < 6 V between J17-pins 5 and 6 to enable the EVM

    According to the instruction you give (short pin 1 pin2 of J1), there will be 48V direct to UVLO pin if R6 doesn't be installed.)

    Best Regards, 

    Nina

  • 0 in reply to Nina Chen
    TI__Genius 12545 points

    Hi Nina,

    It would not get damaged as UVLO will be clamped internally.

    It will be a good practice to keep UVLO below 6V.

    Best Regards,

    Feng