ISL6439 Datasheet, PDF (13/15 Pages) Intersil Corporation – Single Sync Buck PWM Controller for Broadband Gateway Applications

ISL6439, ISL6439A
recommended to minimize the voltage drop across the
bootstrap capacitor during the on-time of the upper
MOSFET. Initial calculations with V_BOOT2 no less than 4V
will quickly help narrow the bootstrap capacitor range.
For example, consider an upper MOSFET is chosen with a
maximum gate charge, Q_g, of 100nC. Limiting the voltage
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_RR, would
have to be added to the gate charge of the MOSFET and
taken into consideration when calculating the minimum
bootstrap capacitance.
ISL6439 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-of-Materials and circuit board description, can be found
in the ISL6439 Application Note.
3.3V
GND
TP₁
4
CT1
C₄
0.22μF
5
CT2
C₁
0.1μF
11
VCC
ISL6439
10
CPGND
1
GND
ENABLE
9
ENABLE
COMP
8
C₁₀
U₁
OCSET ⁶
3
CPVOUT
13
BOOT
14
UGATE
12
PHASE
LGATE ²
FB
7
33pF
R₂
C₁₁
6.49kΩ 5600pF
R₅
1.07kΩ
C₂
1000pF
R₁
TP_{3 9.76kΩ}
C₅
D₁
10μF
Ceramic
C_{7 0.1μF}
C₃
C₆
1μF
L₁
C_8,9
Q₁
R₃
2.26kΩ
R₄ C₁₂
124Ω 8200pF
2.5V @ 5A
GND
FIGURE 8. 3.3V to 2.5V 5A DC/DC CONVERTER
Component Selection Notes:
C_3,8,9 - Each 150μF, Panasonic EEF-UE0J151R or Equivalent.
D1 - 30mA Schottky Diode, MA732 or Equivalent
L₁ - 1μH Inductor, Panasonic P/N ETQ-P6F1ROSFA or Equivalent.
Q₁- Fairchild MOSFET; ITF86110DK8.
13
FN9057.5
November 5, 2008