LM5145: EN/UVLO is pulled low by LM5145

Hi Yihan,

  Can you share the schematic so that we can take a look at the issue?

Gavin

Hi, Gavin:

  If I remove the Ruv2 and Ruv1 is 100ohm, there is no problem. If I change Ruv1 is 100K ohm, some boards work normally and some boards still can not work.

Best regards

Li Yishan

Hi Yishan,

  Please describe the problem in detail. Vin=? Io=?  Please upload the waveforms.

Gavin

Hi Gavin:

     The Vin is 48V. EN/UVLO pin is tied to Vin through 100K resister. But, the voltage is below 1.2V at EN/UVLO pin. The following figure is the waveform at EN/UVLO pin.

Best Regards

Li Yishan

Hi Yishan,

 Can't understand your waveform.  What is the time period for  your shown waveform?  If you connected as you schematic, EN/EVLO pin voltage should be fixed.  Why does it have a jump?

Gavin

Hi, Gavin:

     I also do not understand the waveform and think the EN/UVLO pin voltage should be fixed. But the waveform is true, the time scale is 100ms. LM5145 do not work because the voltage is jumped and below 1.2V. Do you know where the problem is?

Best Regards

Li Yishan 

Hi Yishan,

 I think you can double check .  Put measure the waveform of Vin pin and EN pin voltage together.  Put the two in one page.    

Best Regards

Gavin

Hi Gavin:

     We checked this again and again. There are several LM5145 modules in our product. At first, all of them worked normally. After a while, some of them did not work and and found the  voltage was pulled low at En Pin. In fact, we think there is a prolem for LM5145 uvlo function. We can not explain it except LM5145 uvlo function is wrong. Now, en pin is tied to vin to make LM5145 work normally. 

   By the way, we used the LM5145 modules at past and did not find the above problem. This is not a new design for us. 

Best Regards

Li Yishan