Suggest An IC for the Requirement

Hi,

I would recommend the LM5001 as a negative to positive convertor.  I would configure the part in a similar was as shown in the attached.  You can look at as a boost from 48V to 51V out @ 0.4A see example of the boost designs attached.

 

Design suggestions referring to the PMP Attachment.

 

3. Make Iref (R7) in schematic 3.32k

3.1 Make Rtop (R8) = 3.32k

3.2, Make Rbot ((R21)= 1.21k

See attached Webench design as a boost: Suggest following the PMP FB scheme and implement into the webench design example.  This is a good place to start and get you started.  Hope this helps?

David Baba.

 

webench_design_463344_551_334356789.pdfPMP10525 Schematic Rev 3.pdf

Hi David,Thanks for your reply.
I am bit confuse now. Do you want me to take LM5001 and implement in the PMP design?
Or Using PMP IC i will change the - 48VDC into positive voltage and then go for LM5001 IC?
Why did you take 51VDC as output?
I am looking 3.3VDC output. Could you please elaborate so it will be helpful for me to understand?
Note: I am basically looking for an alternate part for SI9121 IC, which is a Vishay part.
Thanks & Regards,Suman

Hi David,
Shall i implement the FB circuit part in the LM5001 Design? After that can the design be used for -48V input and 3.3V output?
Thanks & Regards,Suman

I was suggesting for analysis purpose only; consider it a 51V output. 48V+3.3V = 51.3V = ~51V. The suggestion I made will still provide a +3.3V output from a -48V input. I could not help notice on the datasheet I downloaded; there is a past date of 2014 for a lifetime buy for the Vishay part? Looking at the SI part, this is exactly what you would be implementing with the LM5001 using a current mirror to provide feedback.

That is correct, yes. if you take the webench design I provided and implement the feedback circuit shown in the PMP design using the values I suggested it will provide you with a +3.3Vout from a -48V in. Hope this helps?

Hi David,

My configuration will be VIN of IC connected to source GND, and GND of IC connected to source 48VDC. In this way i will give -48V as input. If i make 51 VDC as output using boost configuration, then my doubt is as below,

Will i get 3.3VDC w.r.t source GND or w.r.t IC GND?

Thanks & Regards,

Suman

I am not sure I follow your statement in the above post?  The IC Gnd pin is connected to -48V, therefore its return is at -48V.  The Output voltage will be 3.3V out W.R.T Ground (0V).