HIP6006

FN4306 Rev.3.00

Page 9 of 12

April 1, 2005

Ensure that both MOSFETs are within their maximum junction

temperature at high ambient temperature by calculating the

temperature rise according to package thermal-resistance

specifications. A separate heatsink may be necessary

depending upon MOSFET power, package type, ambient

temperature and air flow.

Standard-gate MOSFETs are normally recommended for use

with the HIP6006. However, logic-level gate MOSFETs can be

used under special circumstances. The input voltage, upper

gate drive level, and the MOSFETs absolute gate-to-source

voltage rating determine whether logic-level MOSFETs are

appropriate.

Figure 9 shows the upper gate drive (BOOT pin) supplied by a

develops a floating supply voltage referenced to the PHASE

turns on. A logic-level MOSFET can only be used for Q1 if the

MOSFETs absolute gate-to-source voltage rating exceeds the

MOSFET can be used if its absolute gate-to-source voltage

rating exceeds the maximum voltage applied to PVCC.

Figure 10 shows the upper gate drive supplied by a direct

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

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

VCC less the input supply. For +5V main power and +12 VDC

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

level MOSFET is a good choice for Q1 and a logic-level

MOSFET can be used for Q2 if its absolute gate-to-source

voltage rating exceeds the maximum voltage applied to PVCC.

Schottky Selection

Rectifier D2 is a clamp that catches the negative inductor swing

during the dead time between turning off the lower MOSFET

and turning on 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 will drop one or two percent as a result. The

diode's rated reverse breakdown voltage must be greater than

the maximum input voltage.

Fs is the switching frequency.

+12V

PGND

HIP6006

GND

LGATE

UGATE

PHASE

BOOT

VCC

+5V OR +12V

FIGURE 9. UPPER GATE DRIVE - BOOTSTRAP OPTION

NOTE:

NOTE:

Q1

Q2

PVCC

+5V

OR +12V

D2

+

-

+

-

+12V

PGND

LGATE

UGATE

PHASE

BOOT

VCC

+5V OR LESS

NOTE:

NOTE:

Q1

Q2

PVCC

+5V

OR +12V

D2

HIP6006

GND

+

-