10

source voltage rating determine whether logic-level

MOSFETs are appropriate.

Figure 10 shows the upper gate drive (BOOT pin) supplied

develops a floating supply voltage referenced to the PHASE

conducts. Logic-level MOSFETs can only be used if the

MOSFETs absolute gate-to-source voltage rating exceeds

Figure 11 shows the upper gate drive supplied by a direct

converter systems where the main input voltage is + 5VDC or

less. The peak upper gate-to-source voltage is approximately

for the bias, the gate-to-source voltage of Q1 is 7V. A logic-

level MOSFET is a good choice for Q1 under these

conditions.

Schottky Selection

Rectifier D2 conducts when the upper MOSFET Q1 is off.

The diode should be a Schottky type for low power losses.

The power dissipation in the Schottky rectifier is

approximated by:

In addition to power dissipation, package selection and

heatsink requirements are the main design trade-offs in

choosing the Schottky rectifier. Since the three factors are

interrelated, the selection process is an iterative procedure.

The maximum junction temperature of the rectifier must

remain below the manufacturer’s specified value, typically

specification and the Schottky power dissipation equation

(shown above), the junction temperature of the rectifier can

be estimated. Be sure to use the available airflow and

ambient temperature to determine the junction temperature

rise. HIP6003 DC-DC Converter Application Circuit.

+12V

HIP6003

GND

UGATE

PHASE

BOOT

VCC

+5V OR +12V

NOTE:

Q1

D2

+

-

FIGURE 10. UPPER GATE DRIVE - BOOTSTRAP OPTION

+

-

+12V

HIP6003

GND

UGATE

PHASE

BOOT

VCC

+5V OR LESS

NOTE:

Q1

D2

+

-

P

()

Where: D is the duty cycle = V

V

HIP6003