TPS40055-EP Datasheet, PDF (23/36 Pages) Texas Instruments – WIDE-INPUT SYNCHRONOUS BUCK CONTROLLER

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and from Equation 33, the switching losses can be determined.
TPS40055-EP
SGLS310D – JULY 2005 – REVISED FEBRUARY 2012
(54)
The MOSFET junction temperature can be found by substituting Equation 35 into Equation 34
(55)
5. Calculate synchronous rectifier losses
The synchronous rectifier MOSFET has two loss components: conduction and diode reverse recovery losses.
The conduction losses are due to IRMS losses, as well as body diode conduction losses during the dead time
associated with the anti-cross conduction delay.
The IRMS current through the synchronous rectifier from Equation 38
(56)
The synchronous MOSFET conduction loss from Equation 33 is:
(57)
The body diode conduction loss from Equation 39 is:
(58)
The body diode reverse recovery loss from Equation 40 is:
(59)
The total power dissipated in the synchronous rectifier MOSFET from Equation 41 is:
(60)
The junction temperature of the synchronous rectifier at 85°C is:
(61)
In typical applications, paralleling the synchronous rectifier MOSFET with a Schottky rectifier increases the
overall converter efficiency by approximately 2% due to the lower power dissipation during the body diode
conduction and reverse recovery periods.
6. Calculate the inductor value
The inductor value is calculated from Equation 62.
(62)
A 2.9-µH Coev DXM1306-2R9 or 2.6-µH Panasonic ETQ-P6F2R9LFA can be used.
7. Setting the switching frequency
The clock frequency is set with a resistor (R_T) from the RT pin to ground. The value of R_T can be found from
Equation 63, with f_SW in kHz.
(63)
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