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LM5069: Please Help! LM5069 won't turn on at all

Part Number: LM5069

I have a LM5069 set up very similarly to the recommended application and it never attempts to turn on the gate of the FET.  I see the Timer cap voltage cycling between charging and discharging.  I have checked UVLO and OVLO and both are correct.

I have used almost the exact same circuit successfully on several PCBs.

Any advice of what would cause this?

  • I recommend pulling down the design calculator spreadsheet from www.ti.com/hotswap.  Plug in all of the system parameters paying special importance on total system capacitance this circuit will see.  Include any capacitance down circuit that would be in LC filters of DC_DC converters.  Measure Vin, Vout, Vgate, Vtimer in any data collection.  Most likely a Plim, CL is incorrectly set or you may have a lot of output C and the timer isn't set correctly.  Use the spreadsheet to stay within applications guidelines and avoid SOA issues with the FET you are using.  The same web landing page has excellent app notes and training videos.

    Brian