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LMG5200: Parasitics

Wouter Krikken
Prodigy 60 points
Part Number: LMG5200

Hi,

Is there anything known about the values of the parasitics of the package of the LMG5200? I know it is made to be minimal, but I could not find any values in the datasheet. 

Thanks,

Wouter

  • 0
    TI__Expert 4420 points

    Hi Wouter,

    thanks for you interest in LMG5200.

    Which parasitics are you asking about? I imagine that you would need the power loop inductance for this part, is that correct?

    We typically don't specify them in the datasheet, but if you let me know which ones interest you I can find them out for you.

    Thank you and best regards,

    Alberto

  • 0 in reply to Alberto Doronzo
    Prodigy 60 points
    Hi Alberto,

    Yes, I am mainly interested in the parasitics of the power stage.

    Kind regards,
    Wouter
  • 0 in reply to Wouter Krikken
    TI__Expert 4420 points

    Hi Wouter,

    for power loop inductance, we don't have a package specification, but we model this on the EVM.

    The reference schematic, which is available on our website has a value of 300pH for the entire loop. This is a representation of what the optimized layout described on the specification sheet would yield.

    The TINA reference can be downloaded here:

    LMG5200 TINA-TI Transient Reference Design (Rev. C)

    I hope that this answers your question. If it does please click on the confirm answer button.

    Thank you for your interest!

    Best regards,

    Alberto

  • 0 in reply to Alberto Doronzo
    Prodigy 90 points

    We are using the LMG5200 in a half bridge converter at 4 to 6 MHz (bus voltage 30VDC approx.)
    We already bought the evaluation board and did some test
    At 5 MHz the current consumption without load is about 3 watts(120 mAmp )
    This is much more than we calculated
    We need the Power Derating curves (power dissipation VS junction temp) of the LMG5200, I didn't find it any document.
    Thanks,

    Haim

  • 0 in reply to haim rozenboim
    TI__Expert 4420 points

    Hello Haim,

    thanks for you interest in the LMG5200.

    From my understanding you are running this from a 25V source and at 5MHz you are experiencing 3W of loss.

    From those conditions, if you were doing diode emulation, then the power loss should be ~1W.

    If instead you were running in fixed PWM, with a 4A ripple (around 0A of DC current) you would be close to 1.8W.

    If you could let me know more details of your setup I should be able to replicate it and answer that part.

    Regarding power derating the curve is not given as it depends on the thermal conditions of the environment.

    If you know what the temperature of your board is, and have a reading or estimate of you power loss, you can use the ψ-JB (16C/W) to calculate the junction temperature.

    I hope this points you in the right direction, but please let me know the operating conditions if you need further assistance.

    Best regards,

    Alberto

  • 0 in reply to Alberto Doronzo
    Prodigy 90 points

    The application is to drive a Piezo buzzer

    30 volt p-p

    4-6 MHz

    Load Impedance 20 ohms at resonance

     

      The change we made in EVB are :

    Remove the L1

    Connect one side of the load to the SW

    Connect 2nd  side of the load Half High volt  (by two capacitors)

     

    We Connection to the EVB :

    High volt = 30 volts

    VDD= 6 volts

    Drive 5Mhz 0-5 volt 50%

    And we got good performance (timing and current)

    See sketch for illustration

    For measure the losses we disconnected the load

    And measured current consumption

     On the 30 volt  Power supply

    At 5MHz  current consumption  120 mAmp

    At 3MHz  current consumption  60 mAmp

    At 1MHz  current consumption  10 mAmp

    Is this reasonable?

     

    Thanks

     haim

  • 0 in reply to haim rozenboim
    TI__Expert 4420 points

    Hi Haim,

    thanks for the detailed description.

    Under a simplified model that replaces your piezo with a 20ohm at all frequencies,  the loss inside the LMG5200 comes out to be:

    ~2.5W @5MHz (83mA)

    ~1.5W @3MHz (50mA)

    ~.5W @1MHz (17mA)

    The numbers are quire close as what you are experiencing, the variation in actual impedance of the piezo with frequency probably accounts for the error.

    Notice that in a structure similar to this, you won't have the benefit of soft switching the low-side transistor.

    I hope this provides you some clarification, but I will be happy to answer any further questions.

    Best regards,

    Alberto