LM25118: Setting output 10V@4A

HI Josep,

I also do no see why the LM25118 should not be able to support the 85 Deg.

I will double check with the Webench Team if they can clarify what is triggering this limitation reported here.

But this might take some time to get this info. Will let you know as soon as I get any additional info.

Best regards,

 Stefan

Hello Stefan,

Thank you for your reply. It is OK, meanwhile I will follow the DS and spreadsheet dedicated to this device adjusted to the input/outputs I explained. Only doubt if about selection of external power parts diodes and transisitors. Only reference in spreadsheet is related to High Side Mosfet, nothing about the rest.

I can do following DS if there is information regarding this.

But anyway the most critical is to know if 85ºC is limiting for the IC or not depending on the input/output

thanks

Hi Josep,

the power consumption of the LM25118 depends on the input and also somehow on the output.

For the input the internal LDO generates power losses of (Vin - Vcc) *(I Supply + I low side MOSFET drive)

+ (I low side MOSFET drive)^2 * R Gatedriver

For the output side: depending on that the MOSFET needs to be selected which impacts the losses in the LM25118 (see above)

Now the Rtheta,JA needs to be consider to see if the device is still in the allowed operation condition for 85 Degree ambient.

Best regards,

 Stefan

Hello Stefan,

But it seems that even considering these losses we will reach Tj of 95ºC-100ºC (with Tamb of 85ºC)

I got from datasheet 5,5mA of Vcc consumption and driver of LS Mosfet should be quite low consumption or I am wrong? We are using 11nC of Qgate

Also we are using the supply via Vccx supplied by Vout=10V that should reduce that losses

I am misssing something maybe?

thanks

Hi Jose,

right I expect similar temperature rise, but as the device is spec'ed for 125Deg this should not be an issue.
Therefore i have asked the Webench team to clarify why the are rising this warning. Maybe I miss something.

Note: (to avoid issues later in the application)

Please not if you plan to use Vccx - do not connect Vccx directly to VOUT.

If Vccx should be supplied by VOUT this only should be connected once VOUT as properly powered up, otherwise the device might not start properly.

Best regards,

 Stefan

Hi Jose,

I have not seen an update on this thread for the last 14 days.
So I assume the issue is solved.
In this case it would be great to press the is solved button.

If there is still something open, just let me know with the new details.

Best regards,
 Stefan

Hello Stefan,

I was wondering if you got reply from wbench team regarding the reason of that temperature limitation. That's why I didn't reply anyghing

From my side, I simulated with webench my proposed design at Tamb=60ºC and then I added 25ºC to all thermal results and seems acceptable. Then we will do this design and then we will see

Hi Jose,

thanks for the update - you are right, I just checked the status of the Webench issue - this is still ongoing. 

Let you know once i got an update here.

Best regards,

 Stefan

Hi Jose,

As per my initial observation, WEBENCH design is failing as FET junction temperature is being hit. We need to  update the FET selection. We are looking into this with high priority. We will keep you updated on the same.

Thanks & Regards,
Praveen