ISL6545A Intersil Corporation, ISL6545A Datasheet - Page 14

• Manufacturer Part Number: ISL6545A
• Description: Single Synchronous Buck Pulas Width MoDulation
• Manufacturer: Intersil Corporation

BOOTSTRAP Considerations
Figure 11 shows the upper gate drive (BOOT pin) supplied by
a bootstrap circuit from V
develops a floating supply voltage referenced to the PHASE
pin. The supply is refreshed to a voltage of V
diode drop (V
Check that the voltage rating of the capacitor is above the
maximum V
sufficient for a 12V system. A value of 0.1µF is typical for
many systems driving single MOSFETs.
If V
option is to connect the BOOT pin to 12V, and remove the
BOOT cap (although, you may want to add a local cap from
BOOT to GND). This will make the UGATE V
equal to (12V - 5V = 7V). That should be high enough to
drive most MOSFETs, and low enough to improve the
efficiency slightly. Do NOT leave the BOOT pin open, and try
to get the same effect by driving BOOT through V
internal diode; this path is not designed for the high current
pulses that will result.
For low V
important, an external BOOT diode (in parallel with the
internal one) may be considered. The external diode drop
has to be lower than the internal one; the resulting higher
V
gain in efficiency should be balanced against the extra cost
and area of the external diode.
For information on the Application circuit, including a
complete Bill-of-Materials and circuit board description, can
be found in Application Note AN1257.
G-S
+
CC
-
VCC
ISL6545
of the upper FET will lower its r
+V
is 12V, but V
FIGURE 11. UPPER GATE DRIVE BOOTSTRAP
CC
+ V
GND
CC
D
CC
VCC
-
voltage applications where efficiency is very
D
) each time the lower MOSFET, Q
voltage in the system; a 16V rating should be
LGATE/OCSET
IN
BOOT
UGATE
PHASE
is lower (such as 5V), then another
CC
C
. The boot capacitor, C
14
BOOT
+V
IN
Q1
Q2
DS(ON)
CC
. The modest
V
V
GS
G-S
G-S
less the boot
2
≈
voltage
≈
CC
, turns on.
BOOT
V
V
CC
ISL6545, ISL6545A
CC
and the
- V
,
D
November 15, 2006
FN6305.3