Description
The ISL6700 General Purpose Design Tool
(ISL6700EVAL1Z) is a very simple evaluation board which
can help the user rapidly construct an isolated DC/DC
converter in several configurations. The board consists of
the Intersil ISL6700 Half-Bridge Driver IC, two Intersil
IRFR120 MOSFETs, a bootstrap diode, a bootstrap
capacitor and two input voltage decoupling capacitors. The
ISL6700 can operate at frequencies in excess of 500kHz
and has typical propagation delay times of 30ns. It has
1.25A output drive capability and can switch an IRFR120
load with rise and fall times of less than 20ns.
Application Information
The ISL6700 General Purpose Design Tool
(ISL6700EVAL1Z) is intended for users who have some
experience in power converter design. The 80V rating of the
ISL6700 makes it an ideal choice for many isolated DC/DC
converters, which are point-of-load converters in a
distributed power architecture. To insure adequate design
margin, the maximum voltage that should be applied to this
input should be less than 80VDC. Three possible application
converters are described briefly as follows:
Application #1: Two-Switch Forward Converter
To use the ISL6700EVAL1Z as part of a two-switch forward
converter, the user needs the configuration depicted in
Figure 2. In this topology, both MOSFETs are turned on and
off together, therefore, HI and LI are tied together. The input
signal comes from a pulse-width modulator (PWM)
controller, which is sensing the output voltage (and input
switch current if current-mode control is used). The Schottky
rectifiers clamp the reverse swing of the power transformer
and must be rated to handle the input voltage.
HI
0.1µ
LI
C2
VDD
FIGURE 1. ISL6700EVAL1Z SCHEMATIC
HI
LI
V
DD
2
3
ISL6700
1
U1
D1
HB
4
V
SS
8
5
7
6
HO
HS
LO
®
0.022µ
1
C3
0.47µ
C1
Application Note
ISL6700EVAL1Z General Purpose Design Tool
Q2
Q1
VIN
Q2-S
Q1-D
GND
1-888-INTERSIL or 1-888-468-3774
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
Application #2: Half-Bridge Converter
To use the ISL6700EVAL1Z as part of a half-bridge
converter, the user needs the configuration depicted in
Figure 3. In this topology, the MOSFETs are driven
alternately, with some dead time between turn-off of one and
turn-on of the other. Therefore, HI and LI are driven with
alternating signals PWM
controller.
Application #2: Active-Clamp Forward Converter
To use the ISL6700EVAL1Z as part of an active-clamp
forward converter, the user needs the configuration depicted
in Figure 4. In this topology, the MOSFETs are again driven
alternately, and HI and LI need to be driven alternately as
well. The high-side MOSFET (Q2 in the ISL6700EVAL1Z
board), along with capacitor C
as a means to reset the power transformer in a lossless
manner. This topology lends itself well to running at duty
cycles exceeding 50%, unlike Applications 1 and 2.
PWM
PWM
PWM
FIGURE 2. TWO-SWITCH FORWARD CONVERTER
B
August 12, 2008
HI
LI
HI
LI
All other trademarks mentioned are the property of their respective owners.
PWM
A
PWM
FIGURE 3. HALF-BRIDGE CONVERTER
|
ISL6700EVAL1Z
Copyright Intersil Americas Inc. 2002, 2005, 2008. All Rights Reserved
ISL6700EVAL1Z
Intersil (and design) is a registered trademark of Intersil Americas Inc.
VDD
VDD
BOARD
BOARD
GND
GND
VIN
VIN
A
and PWM
Q1-D
Q2-S
Q2-S
Q1-D
RESET
, is used in this topology
B
ISOLATION
from the PWM
ISOLATION
AN1006.2
SECONDARY
SECONDARY
CIRCUIT
CIRCUIT