LM5007: Convertor goes in to Current limit mode or Shutdown mode with nominal inductor value change

Part Number: LM5007

Dear E2E Expert Team,

I have been using LM5007 design from last 6 years and has zero failure till date.

How ever recently have done changes in inductor design and changed inductor value 100uH/0.6A to 120uH/1A.

With 120uH,my buck design working and gives the output 11.65 for 49VDC input but coil gets heated nearly 45 Centigrade.

However if i switch ON/OFF the input voltage several time then LM5007 suddenly going in to shutdown mode or current limit mode and didnt get recoverd. During this condition output of converter is nearly 2 volt and its oscillating.

Convertor working fine with 100uH/0.6A coil and no problem observed till.

I want to know why LM5007 going in to shutdown mode or current limit mode for 120uH/1A.Please refer the below our regular convertor design for your reference.

  • first_name last_name,

    This device is rated for 500mA. Operating in 1A is hitting current limit. The oscillation is probably the frequency set by the RCL resistor.

    -Sam

  • Dear Sir,

    Thanks.

    I will check for current limit resistor.

    One more thing i want to tell you, I have using this convertor design for 200mA load current which is a basically MCU and relay circuit. Even I am using 120uH/1A inductor but my load current is only 200mA.

    Is this inductor value causes problem or i have to check other things. Please suggest.

  • Arvind,

    Sorry, I misunderstood as 120uH at 1A. My mistake. I wouldn't expect this inductor change to cause an issue like this.

    Inductor heating: Caused by IL^2*DCR and by core losses from switching. Have you double checked that the device is switching at 400kHz (approximate CCM frequency from your conditions)?

    Device latching: Please check VCC during the issue. And please also share scope shots of the SW waveform. Also try placing a 2.2uF (or greater) 100V X7R (or similar) capacitor from VIN to RTN.

    -Sam