Vin>70V / Low min on-time / Low min off-time solution

Hi Chentsu,

LM5116 seems to have a higher input voltage specification compared to LM5145. 100V vs 75V, therefore dependent upon your application, you can select which want that is more suitable with some margin. 

I would check the webench recommended solution given your specification whether it is LM5116 or LM5145. If the LM5145 could not do the simulation, maybe there is some reason that it shows why it could not generate a solution. 

Maybe there is a switching frequency limitation on LM5145 compared to LM5116 for example. 

What i would recommend is try to generate the first pass of the design with webench then you can get an EVM to verify the design. 

Thanks

-Arief

Hi Arief,

Yes, could you please help to check why LM5145 is not the recommended solution in Webench.

BTW, after checking with operation freq., the freq. of LM5145 and LM5116 are all meet duty from 96% to 6%.

So I'd like to figure out why LM5145 can not be used.

Thank you so much,

C.T.

Hi, 

Let me check with webench group

Thanks

-Arief

Hi C.T.

We can look into the reasoning behind why the LM5145 is not being recommended for your design condition in the tool. Would it be possible to share your entire design condition values (VinMin, VinMax, Vout, Iout, Ta, any other advanced option you may be using like specific value of switching frequency?)

Regards,

Amod 

Hi C.T.

Could you please provide the input/output conditions for LM5145. It will help us to debug the issue quickly.

Thanks & Regards,
Praveen B

Hi Amod, Praveen,

Thanks for your help, the parameter is:

1.  50Vin_max / 50 Vin_min / 48V out / 6A / default Temp.

2.  50Vin_max / 50 Vin_min / 3.3V out / 6A / default Temp.

Best regards,

C.T.

Hi C.T,

For the above condition, Vin=50-50V Vout=48V Iout=6A LM5145 hits the minimum off time(140ns) check and WEBENCH fails to create the design. We also don't recommend to create the design for LM5116 since it should also fail for minimum off time check. We will fix the issue soon.

For ideal condition, the minimum off time is calculated as :

Max Duty=Vout/VinMin=48/50=0.96

Min off time=(1-Max Duty)/ Frequency=(1-0.96)/550KHz=72ns

72ns is less than 140ns and hence device hits the minimum off time check. Please reduce the frequency below 250KHz to create the WEBENCH  design for the above condition.

Please find the WEBENCH design for 250KHz here:  webench.ti.com/.../SDP.cgi

For the second condition, Vin=50-50V Vout=3.3V Iout=6A, Design is getting created for LM5145 & LM5116 on WEBENCH since minimum on time(40ns) check is being passed.

For ideal condition, the minimum on time is calculated as :

Min Duty=Vout/VinMax=48/50=0.96

Min on time=Min Duty/ Freq=0.96/550KHz=1.74us

Please let us know if you have any query on the same.

Thanks & Regards,
Praveen B

Hi Praveen,

Got it, thanks for your explaination in detail.

Now the question is, how can I use Webench "auto" calculate frequency for the input parameter?

Or I have to calculate myself and use "NEW DESIGN" to key in the calculated frequency for design creating?

Thank you very much,

C.T.

Hi Praveen,

Understand, thanks for your great help!

Best regards,

C.T.