FN4587 Rev 1.00

Page 14 of 15

April 13, 2005

HIP6019B

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Rectifier CR1 is a clamp that catches the negative inductor

swing during the dead time between the turn off of the

lower MOSFET and the turn on of the upper MOSFET. The

diode must be a Schottky type to prevent the lossy parasitic

MOSFET body diode from conducting. It is acceptable to

omit the diode and let the body diode of the lower MOSFET

clamp the negative inductor swing, but efficiency might drop

one or two percent as a result. The diode's rated reverse

breakdown voltage must be greater than twice the maximum

input voltage.

PWM2 MOSFET and Schottky Selection

The power dissipation in PWM2 converter power devices is

similar to PWM1 except that the power losses of the lower

device are representative of a Schottky diode instead of a

MOSFET. The transistor power losses follow the PWM1

upper MOSFET equation, so the selection process should

be somewhat similar. The equation below describes the

conduction power losses incurred by the Schottky diode.

As it can be observed, conduction losses in the Schottky

Linear Controller MOSFET Selection

The main criteria for selection of MOSFET for the linear

regulator is package selection for efficient removal of heat.

The power dissipated in a linear regulator is:

Select a package and heatsink that maintains the junction

temperature below the maximum rating while operating at

the highest expected ambient temperature.

+12V

PGND

HIP6019B

GND

LGATE

UGATE

PHASE

+5V OR LESS

NOTE:

NOTE:

Q1

Q2

+

-

FIGURE 14. OUTPUT GATE DRIVERS

CR1



–





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=

–





=