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LM5145-Q1: LM5145-Q1

Venu Gopal
Prodigy 90 points
Part Number: LM5145-Q1
Other Parts Discussed in Thread: LM5145

Hi team,

This is Venu Gopal.

I have an issue with IC LM5145-Q1. I have five DC-DC converter circuits in series on a PCB which are designed for 24V and 8A each. This each Converter output again divided into 5 parallel outputs each 1.5A/24V. When i checked the individual circuits i got expected output voltage at converter stage as well as at the parrel outputs. when I turned on all together only first and second circuits giving expected output voltage remaining circuits are not giving 24V. I found that MOSFET Gate and Source is shorted. Now I have changed the MOSFET's still I am not getting the output voltage. I am not getting any gate pulse at the MOSFET Gate Pin. I am attaching Schematics for your reference. 

Similar five circuits in series on the PCB. 

  • 0
    TI__Guru 69027 points

    Hi Venu,

    Please send the completed quickstart file for this design.

    I'm not totally clear on how your power tree is setup. Are the 5 x 24V/8A outputs connected in parallel? And the loads are 5 x 1.5A - are these DC/DC regulators?

    The main thing in the schematic is that the snubber caps at 100nF are way too high, giving huge FET loss. Try 220pF as a starting point. One only snubber RC network is needed, typically across the low-side FET.

    Regards,

    Tim

  • 0 in reply to Timothy Hegarty
    Prodigy 90 points

    Hi Timothy,

    I hope the following image will finds you well to explain in detail about my query. OUT 1, OUT 2, OUT 3, OUT 4, OUT 5 are the 24V/1.5A are the parallel outputs takes from the LM5145 Converter output. When I turned on individually, they gave expected output voltage as well as output current. When I turned on all together OUT 3, OUT 4, OUT 5, are not giving expected output voltage. I did impedance check I got to know that High side MOSFET GATE and SOURCE pin are shorted. I have replaced the High side MOSFETS of all 3 outputs with new one. still, I am not seeing any gate pulse at the High side MOSFET (Q1 in the Schematic file) of LM5145-Q1 when I turned on Circuit.  When I turn on all 5 outputs together it happened what may be the reason and how to resolve it. IN this case with New MOSFETs also we are not getting any pulse at the GATE pin. IS this the indication of IC shorting or IC failure?

    The following image is one set of circuit on the PCB, like these 5 circuits are there on the PCB in series each will have OUT 1, OUT 2, OUT 3, OUT 4, OUT 5.