ISL6526 Intersil Corporation, ISL6526 Datasheet - Page 12

• Manufacturer Part Number: ISL6526
• Description: Single Synchronous Buck Pulse-Width Modulation (PWM) Controller
• Manufacturer: Intersil Corporation

The minimum bootstrap capacitance can be calculated by
rearranging the previous equation and solving for C
Typical gate charge values for MOSFETs considered in
these types of applications range from 20 to 100nC. Since
the voltage drop across Q
simply V
minimize the voltage drop across the bootstrap capacitor
during the on-time of the upper MOSFET. Initial calculations
with V
bootstrap capacitor range.
ISL6526 DC-DC Converter Application Circuit
Figure 8 shows an application circuit of a DC-DC Converter.
Detailed information on the circuit, including a complete Bill-
Component Selection Notes:
C
BOOT
C
D1 - 30mA Schottky Diode, MA732 or Equivalent
L
Q
1
3,8,9
1
- 1µH Inductor, Panasonic P/N ETQ-P6F1ROSFA or Equivalent.
- Fairchild MOSFET; ITF86110DK8.
BOOT2
CPVOUT
=
- Each 150µF, Panasonic EEF-UE0J151R or Equivalent.
---------------------------------------------------- -
V
BOOT1
3.3V
GND
no less than 4V will quickly help narrow the
ENABLE
Q
- V
GATE
–
D
V
. A schottky diode is recommended to
BOOT2
0.22µF
C
LOWER
4
12
TP
1
is negligible, V
10
4
5
1
9
CT1
CT2
CPGND
GND
ENABLE
COMP
8
FIGURE 8. 3.3V TO 2.5V 5A DC-DC CONVERTER
6.49kΩ
0.1µF
C
R
ISL6526
1
2
BOOT1
33pF
C
VCC
10
BOOT
11
5600pF
C
11
is
.
FB
CPVOUT
ISL6526
OCSET
UGATE
PHASE
7
LGATE
BOOT
1.07kΩ
U
R
1
5
13
14
12
6
3
2
For example, consider an upper MOSFET is chosen with a
maximum gate charge, Q
drop across the bootstrap capacitor to 1V results in a value
of no less than 0.1µF. The tolerance of the ceramic capacitor
should also be considered when selecting the final bootstrap
capacitance value.
A fast recovery diode is recommended when selecting a
bootstrap diode to reduce the impact of reverse recovery
charge loss. Otherwise, the recovery charge, Q
have to be added to the gate charge of the MOSFET and
taken into consideration when calculating the minimum
bootstrap capacitance.
of-Materials and circuit board description, can be found in
Application Note AN9994..
TP
D
C
124Ω
1
7
3
R
2.26kΩ
4
R
1000pF
3
0.1µF
9.76kΩ
8200pF
C
R
C
2
1
12
Ceramic
C
10µF
5
Q
g
, of 100nC. Limiting the voltage
1
C
C
1µF
6
3
L
1
C
8,9
2.5V @ 5A
RR
GND
, would