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LM5060-Q1: Repeat start-up instead of turn off the FETs directly.

Jinpeng Xing
Prodigy 40 points
Part Number: LM5060-Q1
Other Parts Discussed in Thread: LM5060

Hello,

In our design, the LM5060 will be driving Bridge-circuit acting as high-switches for a PMSM. When testing with resistive loads (use electronic load,0.3R), OCP works unexpectedly and the LM5060 does not turn off the FETs.And the voltage of GATE pin repeat start-up instead of shut-off directly(enclosure is a scope shot, GATE is CH1 and CURRENT is CH2(10A/V)).

Schematic included below.

In the final design, we plan to have the OCP trip point set at 70A. So far, these tests have been with a trip point set at 25A. I would like to understand why I'm seeing these and if there is anything that can be done to fix OCP capabilities.

best regard,Xing

  • 0
    TI__Guru** 105361 points

    Hi Xing,

    I will look into this issue and reply early next week.

    Best Regards, Rakesh

  • 0 in reply to Rakesh
    TI__Guru** 105361 points

    Hi Xing,

    Can you share your OCP calculation sheet.

    What is the operating voltage ? Can you test with resistive load and share test waveform of Vout, GATE, Timer and input current in a single scope shot. 

    Best Regards, Rakesh

  • 0 in reply to Rakesh
    Prodigy 40 points

    Hi Rakesh

    Thank you very much for your reply.

    My OCP calculation references the ‘’Typical Applications-8.2.1.2.1’’ of LM5060’s DATASHEET:

    Idsth*Rdson=Isense*Rsense , Rdson=2mR,Idsth=25A

    waveform test condition VIN =12.56V.

    enclosure is the scope shots, GATE is CH1 ,VOUT is CH2 , TIMER is CH3 and CURRENT is CH4(10A/V)

    best regard,Xing.

  • 0 in reply to Jinpeng Xing
    TI__Guru** 105361 points

    Hi Xing,

    Looks like the device is going into UVLO reset. Can you remove R46 in your schematic and test again.

    Best Regards, Rakesh

  • 0 in reply to Rakesh
    Prodigy 40 points

    Hi Rakesh

    Thank you very much for your reply.

    I have removed the R46 as you said,but the question still exists.

    And I find something about the pin UVLO (the same as VIN) ,the details as follow.

    And I also find that LM5060 have different frequencies of GATE when I compared Battery with Stabilized Voltage Supply(Battery is lower and has the same question).

    Enclosure is the scope shots, GATE is CH1 ,VIN is CH2 , TIMER is CH3 and CURRENT is CH4(10A/V).

    best regard,Xing.

  • 0 in reply to Jinpeng Xing
    TI__Guru** 105361 points

    Hi Xing,

    The system is going into current limit and turning off. It is the ringing at Vin which is causing the device to restart. Add 1uF from Vin (pin 2) to ground, Remover R46 and remove R50.Please test again and let me know if it helps.

    Best Regards, Rakesh

  • 0 in reply to Rakesh
    Prodigy 40 points

    Hi Rakesh

    Thank you very much for your reply.

    I have removed the R50 and add 10uF(1uF is not obvious) from Vin to ground as you said,then the repeat-start question is solved finally.

    But the VIN still rings, although the amplitude is smaller,and if there is anything that can be done to fix this ring.

    Enclosure is the scope shots, GATE is CH1 ,VIN is CH2 and CURRENT is CH4(10A/V).

    Thank you very much again.

    best regard,Xing.

  • 0 in reply to Jinpeng Xing
    TI__Guru** 105361 points

    Hi Xing,

    Your input source impedance seems to be high. Please add enough decoupling cap across C55 to compensate

    Best Regards, Rakesh