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ISL6520B

Single Synchronous Buck Pulse-Width Modulation (PWM) Controller

Intersil 

ISL6520B

circumvented by these MOSFETs if they have large parasitic

impedences and/or capacitances that would inhibit the gate

of the MOSFET from being discharged below it’s threshold

level before the complementary MOSFET is turned on.

+5V

DBOOT

VCC

ISL6520B

+ VD -

+5V

BOOT

CBOOT

Q1

UGATE

PHASE

+-

Q2

LGATE

GND

NOTE:

VG-S ≈ VCC -VD

NOTE:

VG-S ≈ VCC

FIGURE 6. UPPER GATE DRIVE BOOTSTRAP

Figure 6 shows the upper gate drive (BOOT pin) supplied by a

bootstrap circuit from VCC. The boot capacitor, CBOOT,

develops a floating supply voltage referenced to the PHASE

pin. The supply is refreshed to a voltage of VCC less the boot

diode drop (VD) each time the lower MOSFET, Q2, turns on.

ISL6520B DC-DC Converter Application

Circuit

Figure 7 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

Application Note AN9932.

+5V

50kΩ

10.0kΩ

8200pF

1.00kΩ

0.1µF

ISL6520B

VCC

5

POR

AND

SOFT START

+

CIN

2 x 330µF

1 BOOT

COMP/SD 7

REF

470pF

+-

FB 6

U1

OSC

2 UGATE

8 PHASE

+-

4 LGATE

3

GND

3.16kΩ

60.4Ω

18000pF

2 x 1µF

D1

0.1µF

Q1

L1

VOUT

Q2

COUT +

0.1µF

3 x 330µF

Component Selection Notes:

CIN - Each 330mF 6.3WVDC, Sanyo 6TPB330M or Equivalent.

COUT - Each 330mF 6.3WVDC, Sanyo 6TPB330M or Equivalent.

D1 - 30mA Schottky Diode, MA732 or Equivalent

L1 - 3.1µH Inductor, Panasonic P/N ETQ-P6F2ROLFA or Equivalent.

Q1, Q2 - Fairchild MOSFET; HUF76143.

FIGURE 7. 5V to 3.3V 15A DC-DC CONVERTER

8

FN9083.2

January 20, 2005

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