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LM5101C: LM5101C was shorted between D and S of FET.

Bob Lee62837
Mastermind 7230 points
Part Number: LM5101C
Other Parts Discussed in Thread: SN6505B

Dear support member,

My customer used LM5101C.
Low side driver don't use, but only High side driver use.

I attacheded file about circuit.
Is there a problem with this circuit diagram?


When the power was turned on,
the IC raised smoke, short circuit between D and S of FET.

Could you check attached file?


Best regard.
Bob Lee.

LM5101C_Question_180319.pdf

  • 0
    TI__Mastermind 20950 points
    Hello Bob,
    I am an applications engineer with the High Power Driver group and will work to resolve your concerns. The schematic looks OK in general but I do have some questions about the details.
    Can you provide the diode part number of D2? This should be a fast recovery diode, or schottky to minimize the reverse current when Q1 turns on in continuous current conduction.
    I see the Wave is specified at 0 to 10 kHz. Can you provide more detail on this range? Does the circuit need to work at 0Hz or DC with Q1 being turned on, or turned off? What is the lowest operating frequency, excluding DC, when Q1 is switching, and what is the longest Q1 on time?
    For DC and low frequency operation, the value of the boot strap capacitor (C2) needs to be reviewed since there is quiescent current from HB to HS. This will result in HB declining over time.
    If Q1 needs to be turned on in a DC state, there will need to be a floating bias supply for the HB to HS bias.

    Regards,
    Richard Herring
  • 0 in reply to Richard Herring
    TI__Guru**** 189399 points
    Hi Bob,

    Since we didn't hear back from you, we must assume this issue is resolved. If not, let us know, and we will work with you to resolve it.
  • 0 in reply to Don Dapkus
    Mastermind 7230 points

    Dear Don Dapkus,

    I'm sorry. I was late for confirmation.
    I confirmed te details.


    （Feed back contents)
    ・The diode part number of D2 is D3FJ10.

    ・Wave is fixed at 100 kHz.
    Duty is also varied from 0% to 90%.
    DC operation is not necessary. ON duty 90% is the maximum.

    （My customer's thought)
    As customer's thought,
    100 Ω was connected between HS and GND to prevent the IC from being damaged.

    Q1.
    Is there any problem with this measure?

    （Different problem）
    As a different problem,
    By connecting a 100 Ω resistor,
    When it turns ON several hundred ms after turning OFF once,
    Since it is not output from HO, Q1 would being OFF.


    Q2.
    Is this phenomenon affecting charging / discharging of the BOOT capacitor?
    Are there other causes?


    Best regard.
    Bob Lee.

  • 0 in reply to Bob Lee62837
    TI__Mastermind 20950 points

    Hello Bob,

    Thank you for confirming the status of this concern with the LM5101C in the buck converter design. The D3FJ10 for D2 should be OK for this application since schottky diodes are fast recovery.

    Regarding the question about the 100 Ohms from HS to ground.

    The 100 Ohm resistor from HS to ground will ensure that the HS node has a current path to ground to charge the boot strap capacitor. This will allow charging of the boot strap capacitor on initial power up, and in conditions where the inductor current is not continuous. 

    For the question of "when it turns on several hundred milliseconds after turning off once, since it is not output from HO Q1 would be turning off".

    Can you clarify this condition. Is the several hundred milliseconds a power up and power down sequence? The Fsw is stated as 100khz, so that period is 10us. Can you confirm if there is voltage on the output during this time sequence? If there is voltage on the output this would also prevent the HS node going low enough to charge the bootstrap capacitor.

    Regards,

    Richard Herring

  • 0 in reply to Richard Herring
    Mastermind 7230 points

    Dear Richard Herring,

    Thank you very much for reply.

    As I want to send you waveform,
    Would you teach me private E-mail address?

    Best regard.
    Bob Lee.

  • 0 in reply to Bob Lee62837
    TI__Mastermind 20950 points
    Hello Bob,
    Can you "friend" me, then you can send the files in the PM interface.
    Regards
    Richard Herring
  • 0 in reply to Richard Herring
    Mastermind 7230 points

    Dear Richard Herring,

    Thank you very much for reply.

    I don't know how to do PM Interface.
    I applied friendship request for a while ago, can I send e-mail with this?

    Best regard.
    Bob Lee.

  • 0 in reply to Bob Lee62837
    Mastermind 7230 points

    Dear Richard Herring

    I attached file about waveform.

    Could you check attached file?


    Best regard.
    Bob Lee.

    LM5101C_Question_180416.pdf

  • 0 in reply to Bob Lee62837
    Mastermind 7230 points

    Dear Richard Herring,

    Could you teach progress situation?

    Best regard.
    Bob Lee.

  • 0 in reply to Bob Lee62837
    TI__Mastermind 20950 points

    Hello Bob,

    We regret that the PM interface to be able to send messages did not work well for you. In reviewing the waveforms, the Vout is taking quite some time to decline after the switching stops. Since HS will be equal to Vout when the converter is not switching the C2 boot capacitor will be very slow to charge completely to the VDD level.

    It is difficult to read the exact values of C2 but it appears the HB-HS is below UVLO when HI goes high.

    Does this application require full DC operation of the HO output? If that is the case, the voltage on C2 cannot be sustained with the bootstrap diode charging method.

    Regards

    Richard Herring

  • 0 in reply to Richard Herring
    Mastermind 7230 points

    Dear Richard Herring,

    Thank you very much for reply.

    This application need to full DC operation of the HO output.
    Is there no countermeasure in the bootstrap diode charging method, right?

    Best regard.
    Bob Lee.

  • 0 in reply to Bob Lee62837
    TI__Mastermind 20950 points

    Hello Bob,

    There is a solution for the high side floating MOSFET drive in DC applications. Since the operation needs to be DC there will need to be a dedicated floating bias supply for the HB-HS high side bias. There is a TI design which features the SN6505B transformer driver for isolated bias supplies.

    The link for the TI design is:

    The link for the SN6505B transformer driver is:

    Let me know if you have any questions on the proposed solution for the floating bias to support DC operation.

    Regards,

    Richard Herring

  • 0 in reply to Richard Herring
    Mastermind 7230 points

    Dear Richard Herring

    Thank you very much for reply.


    Design using SN6505B is too diffcult to use.
    Because cost and space change from the present situation.

    Can there no countermeasure with Capacitor, diode, resistance discrete parts, right?


    Best regard.
    Bob Lee.

  • 0 in reply to Bob Lee62837
    TI__Guru**** 189399 points
    Hi Bob,

    In order to run a high-side driver at DC, you need some kind of isolated power supply.

    Looking at your schematic, I don't think dc operation is really required, is it?

    Did you solve this issue?