
RC5054A
PRODUCT SPECIFICATION
10
P
Figure 7. Upper Gate Drive - Bootstrap Option
Figure 8 shows a similar circuit for 12 Volt power input
applications with two major differences. D
Boot
has been
replaced with a 5.1 Volt Zener diode and a small resistor
(5
W
-10
W
) is inserted in series with C
Boot
. This circuit will
deliver the necessary drive voltage for Q1 while maintaining
a safe operating voltage on pin 15 (Boot).
Figure 8. Upper Gate Drive -
Bootstrap Option-Server Application
Figure 9 shows the upper gate drive supplied by a direct con-
nection to V
CC
. This option should only be used in converter
systems where the main input voltage is +5V
DC
or less. The
peak upper gate-to-source voltage is approximately V
CC
less
the input supply. For +5V main power and +12VDC 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 V
CC
.
Figure 9. Upper Gate Drive - Direct V
CC
Drive Option
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.
+12V
+5V
PGND
RC5054A
GND
LGATE
UGATE
PHASE
BOOT
VCC
NOTE:
V
G-S
V
CC
-V
D
NOTE:
V
G-S
V
CC
C
BOOT
D
BOOT
Q1
Q2
+
-
D2
+ V
D
-
+12V
+12V
PGND
RC5054A
GND
LGATE
UGATE
PHASE
R
BOOT
VCC
NOTE:
V
G-S
V
CC
-V
D
NOTE:
V
G-S
V
CC
C
BOOT
D
BOOT
Q1
Q2
+
-
D2
+ V
D
-
+12V
PGND
RC5054A
GND
LGATE
UGATE
PHASE
BOOT
V
CC
+5V OR LESS
NOTE:
V
G-S
V
CC
-5V
NOTE:
V
G-S
V
CC
Q1
Q2
+
-
D2