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LM5116: Power management forum

Bindu Subramanyam
Prodigy 70 points
Part Number: LM5116
Other Parts Discussed in Thread: LM5145, LM5141,

hello TI

I Have been working on LM5116MH/NOPB Buck Converter

WEBENCH Design (values from data sheet): MOSFET is "BSC117N08NS5ATMA1" [5V]

 Input voltage 9V-60V., Output voltage 5.25V., Output current 10A., MOSFET total power dissipation 1.812 W., MOSFET switching losses 1.603 W., Switching frequency 395.432 kHz., 

As per the equation mentioned below from the reference document "Power Loss Calculation With Common Source Inductance Consideration for Synchronous Buck Converters " with the values from datasheet, we're not able to get the exact loss.

Our values are Vin=60V., Iout=.10A .,Switching frequency=292.8Hz., Qgs2=13nC., Qgd=7nC., Ig=100nA.,


So, for calculating switching losses I used a formula for switching loss  but I dint got the expected results 

 

As per the WEBENCH design the suggested MOSFET is "BSC117N08NS5ATMA1". And the switching Power loss is "1.603 W" For 5V with Input voltage 9V-60V., Vout=5.25V., Iout=10A.

  • 0
    TI__Guru 74052 points

    Hi Bindu,

    Take a look at the LM5145 75V controller and its quickstart calculator https://www.ti.com/tool/LM5145DESIGN-CALC.

    This allows you to review MOSFET power losses based on the entered parameters. Note the LM5145 EVM is setup for 5V/20A/225kHz with 80V FETs (the high-side FET is the same as mentioned above). 5.25V/10A shouldn't be a problem.

    Regards,

    Tim

  • 0 in reply to Timothy Hegarty
    TI__Guru 74052 points

    As an alternative, take a look at the LM5141 65V controller. Note it has a VCCX pin for external bias supply, so it accepts 5.25V from the output (unlike the LM5145/6 and LM5116 that prefer >8V). This helps with IC power loss at high Vin as the VCC current of the controller is derived from VOUT and not VIN. However, the LM5141 gate drive amplitude is 5V, so it requires logic-level FETs with Rdson rated for Vgs = 4.5V.

  • 0 in reply to Timothy Hegarty
    Prodigy 70 points

    Hai Tim,

    Thankyou for reacting on my question. After clearly referring to LM5145 75V Excel sheet you provided I didn't find any equation related for my calculation but i changed the values(as shown below) in the Excel according to LM5116 values.

    My WEBENCH (LM5116) circuit has high side loss is 1.8W and low side is 3.58W 

    by placing my WEBENCH values in the LM5145 Excel sheet i didn't get the expected loss so i would i like to ask share the respective equation used in the excel sheet.   And i have already designed my physical setup with LM5116 so i am requesting you to provide a equation.

  • 0 in reply to Bindu Subramanyam
    TI__Guru 74052 points

    Hi Bindu,

    The applicable equations are given in a table in the apps sections of the LM5145 datasheet.

    You may want to use a slightly lower Rdson FET for the low-side position (based on the duty cycle being less than ~50%).

    Regards,

    Tim