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LM5116 VCCX current consumption

Oystein Johnsen
Prodigy 140 points
Other Parts Discussed in Thread: LM5116, LM25116, LM5116WG, LM5113, LM5025

Hi.

I've got an LM5116 evaluation board up and running with two MOSFET's on it.  Input voltage is 24V, and output voltage is currently -24V, for testing purposes.  And I'm curious about the current consumption when supplying the MOSFET gate voltage on the VCCX pin.

We adjusted the voltage on the VCCX pin to 7.4V - same as the internal regulator in the LM5116.  The current draw from the 7.4V is around 16mA, while around 97mA from 24V supply.  In other words, a 118mW consumption from the 7.4V supply.  Now, when turning off the 7.4V supply, the current draw from the 24V supply increases to around 137mA - an increase of 40mA, or 960mW.  This gives a difference of almost 850mW in power consumption.  Why is this?

We're also testing with GaNFET's instead of MOSFET's.  The supply on the VCCX pin is then reduced to 5.5V, because of a 5V limit on the GaNFET gate (0.5V drop from the VCCX pin to the high and low side gates).  With a GaNFET on both high and low side, the current draw from the 5.5V supply is around 130mA, almost ten times higher than with MOSFET's.  Using one GaNFET (high side) and one MOSFET (low side), the current draw drops to around 60-70mA.  Do you know why the GaNFET's eats so much current from the LM5116?

  • 0
    TI__Guru 58171 points

    Hi

    If you configure the LM5116 Evaluation board for +24V input and -24V output as a inverted buck boost , from the controller point of view supply voltage is equal with 48V (24+24=48) which is greater than 42V maximum supply voltage range.

    Ideally, IVIN = IVCC+1mA, IVCC=IVCCX, maximum IVCC=25mA.

    In your case, IVIN should be < 2mA with external VCC supply.

    Regards,

  • 0 in reply to EricLee
    Prodigy 140 points

    Hi.

    Thanks for your answer, but I wonder if you aren't incorrect in your initial comment...?  According to the parameter overview on TI.com, it says that the maximum supply voltage range for LM5116 and LM5116WG is 100V.  For LM25116 it is, as you say, 42V.

    Our design is based on a +24V input and a -48V output, but we reduced the output voltage to -24V for testing purposes.

    So the first question, in regards to higher power consumption if MOSFET's are supplied with voltage from VIN rather than VCCX, is still open.  We've verified this behavior on two boards, so I don't think this is caused by a faulty controller.

    The second question about the GaNFET's might be a faulty controller, though.  When mounting GaNFET's on a different evaluation board, the current draw dropped to 8mA from the VCCX supply.  It was running in diode emulation mode, though.  But as far as you know, the LM5116 controller should be able to support one EPC2001 GaNFET on both top side and bottom side?

    BR,
    Øystein Johnsen. 

  • 0 in reply to Oystein Johnsen
    TI__Guru 58171 points

    Hi

    You are right. LM25116 is up to 42V. LM5116 is 100V.

    LM5116 is not designed for GaN FET. Please refer LM5113 GaN driver at www.ti.com

    About the VCC, VIN and VCCX current, would you set-up your board for +48Vin to +24Vout and then measure them again ?

    As you know, from the IC point of view, +48V to +24V configuration should be same as +24 to -24V configuration. If there are differences of the VCC, VIN, VCCX current between these two configurations, you may find the hint / answer from there.

    Regards,

     

  • 0 in reply to EricLee
    Prodigy 140 points

    Hi.

    Sorry for the late reply.

    We've been looking into why the GaNFET's were drawing so much current from the VCCX supply, and believe it has to do with too high a voltage on the gate pin out to the GaNFET's.  Even with a 5V supply on the VCCX pin, the ringing on the switch node caused the voltage built up over the boot strap capacitor to exceed the 6V absolute max limit of the GaNFET's.  So we need something that clamps the gate voltage to a level below the max limit.

    The LM5113 is only a GaNFET driver, and not a controller.  Is it possible to use the LM5113 in combination with LM5116?  Else, what kind of controller would you suggest we use that has more or less the same features as the LM5116 is regards to protection, current sensing etc.?

    Thanks.

  • 0 in reply to Oystein Johnsen
    TI__Guru 58171 points

    Hi

    Sorry. I don't have information about PWM controller without drivers.

    Regards,

  • 0 in reply to EricLee
    Expert 2305 points
    There is a LM5113 demo board, that uses a LM5025 and a LM5113 to drive some EP2001 GanFETS ( www.ti.com/.../lm5113llpevb )

    Using a 5116 with a LM5113 might be a useful combination, no external error amplifer is needed.. and the abilty to use VCCx to provide power is very helpful.