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LTC3892 overheating

I am using the LTC3892 for dual 9A 36V outputs. I have noticed that using one channel/side of the LTC3892 everything works but as soon as I turn on the other side the voltages start turning on and off and the the LT3892 gets hot. 

I am powering the chip using and external 12V power rail (extVcc) with the driver selected for 10V.  The switching frequency is 202khz and the transistors I am using(csd18532q5b) have a gate charge of 44nC at 10V.  Hence for the two transistors per side there should be around 18mA of current, well below the 50mA spec per side. Also with 2V LDO drop this should only be  36mW (72mW with both sides on). 

Is there something else I should look at with the part as to why it is getting hot? 

Thanks

Trampas

  • Hi Trampas,

    I am not sure how you enable one channel then turn on the other side.

    If you are doing 2-ph single output, please follow the datasheet recommendation of the pin connections.

    Datasheet page 38 fig 14 gives a good example. The DC2190A-B is also an example to follow.

    In these examples, RUN, FB, ITH and SS pins are tied together.

    Thanks,

    Ding

  • I am using chip as two independent outputs, hence I enable each side

    independently using the Run pins.

    The datasheet indicates there is two LDOs, one per side, however there is

    only one capacitor for both LDOs is this correct?

    Thanks

    On Mon, Jun 11, 2018 at 4:25 PM, Ding.Li <

  • There is only one LDO inside the LTC3892.

    Therefore, only one decoupling capacitor is needed.

    Enabling both channels doubles the LDO power loss.

    Hence higher temperature rise is expected.

    However, only the higher temp rise does not necessarily cause Vo on and off.

    There must be something else going on.

    Try capturing some waveforms of this abnormal event so that we can discuss more.

    Thanks

  • Looking more the input power was cycling on/off due to over current.

    The Datasheet specifically states that the LTC3892 contains two LDOs. The

    only concern with the LDO is the current rating. That is, is there 50mA for

    both sides are per side?

    On Mon, Jun 11, 2018 at 4:53 PM, Ding.Li <

  • One LDO is powered by VIN and the other is powered by EXTVCC.

    Only one LDO is active at one time, either from VIN or from EXTVCC, but not both.

    In your case, power is from the EXTVCC, which should not cause high temp rise.

    Please check if each channel is switching regularly, one at a time.

    Thanks,

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    EZ Admin