Datasheet LTC4370

Background: I want to use this chip to combine the power output of two 2.4A USB ports on a USB power bank I have. If this is possible it will output ~25W and w/ my dc-dc converter I should be able to charge my laptop using USB power banks. If possible in the future I may buy 2 chips more to combine 4 USB outputs.

I presume I will be using a design very similar to the typical application on the first page of the datasheet, but with the values listed in the 5V example on page 14. I might need to adjust the resistor on the range pin depending on how close the Vout on the USB ports will be.

Question: page 11 of the datasheet, MOSFET selection, the last paragraph's phrasing confuses me. I can't tell if it wants me to get a Rds(on) value as close to what the equation gives, or if that is a maximum value for Rds(on) and anything below should suffice. The given equation is ΔVIN(SH) = VFR(MAX) – 0.5IL • RDS(ON),

VFR(MAX) is the maximum forward regulation voltage (Vin-OUT) Vin(sh) is the "sharing capture range"...not sure what that means what IL is has proven elusive as well... wish I knew what these all were

I could always use a very similar MOSFET to the SUM85N03-06P in the typical application, and ignore the equation altogether but avoiding errors would be cool, and who doesn't like to learn?

  • 1
    \$\begingroup\$ Your DS LINK is wrong. \$\endgroup\$ – Andy aka Apr 26 '17 at 18:43

It means that you need to consider the drop across the mosfet when your considering the voltage that the device can supply.

\$ \frac{I_L}{2}*Rds_{on} = V_{across mosfet}\$

this needs to be lower than 75mV for lower operation. So take your maximum load divide it by two and multiply it by Rdson then make sure its lower than 75mV for optimal performance. That number will also affect your regulated voltage as the mosfet will have a voltage drop across it.


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