LM25117: compare with LM25148

Hi Eric,

but I notice LM25117 has better driving capability, which allow customer more flexibility to pick MOS

what do you think?

hi eric,

thanks Eric, got it

why can't I calculate MOS power loss in calculator?

any alternative?

Hello Fred

I found a calculator on TI.COM https://www.ti.com/tool/SYNC-BUCK-FET-LOSS-CALC . 

- Eric Lee

Hi Eric,

one question here,

so for LM25117, VCC is default connecting to Vin right?

we don't have to connect anything to VCC if we want to use Vin supply which in definition is not external supply?

Hi Eric,

got it,

if I connect VCC to Vout (12V)

does this mean switching loss of MOS will be lower since the VCC is 12V instead of 7.6V ?

Hello Fred 

The switching loss of the MOSFET and the power loss of the IC can be reduced.  

- Eric Lee

Hi Eric,

when VCC is 12V.

actually, I think the MOS switching loss will reduce since  the VCC sourcing current will be faster (12V > 7.6V)

under same driving resistance. what do you think?

Hello Fred 

Rdson loss will be reduced but the gate driving loss will be increased,  because the MOSFET driving voltage is increased from 7.6V to 12V.

Which means efficiency might be reduced at the light load or if low current applications, but the heavy load efficiency can be improved especially when the switching frequency is low.

-  Eric Lee

HI Eric,

how about the rise/fall time of MOS Vgs,  should be faster, right?

Hello Fred

It is not easy to estimate because the Vgs slope will be steeper but the Vgs should reach at 12V (not 7.6V). Yes, the MOSFET switching loss will be smaller. I will correct the previous post.

- Eric Lee

Hi Eric,

why Vgs is not 12V but 10V, I thought it would be as same as VCC?

thanks

Thanks for promoting BSR-WV devices. Please feel free to contact me if you have any questions.
- Eric Lee (Applications Engineering)

Hi Eric,

1.just want to confirm with you that LM25117 with "12V VCC"  is capable to have lower "high-side MOS" switching loss than LM25148  ?

under same frequency, same 20A load and same MOS. which one has better driving performance?

2.  the MOS loss in calculator is way lower than the result of the MOS tool you gave above.  

do you know why there's a huge error between both tool?

HI David,

thanks a lot for your material, it helps.

so in conclusion, although LM25149 has lower driving resistance (2x) ,

the LM25117 has flexible VCC which can increase the speed that charges the miller plateatu.

so LM25117 essentially has better driving capability , right?

but just curious, why doesn't LM25149 has adjustable VCC if it's the newer one?

Hi  David,

got it , so this is for the cost , I see.

BTW, which package of LM25117 is popular in market and recommended?