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AN1021
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Copyright © Intersil Americas Inc. 2002. All Rights Reserved
P R E L I M I N A R Y
Embedded DC-DC Converters Using ISL6526 and
ISL6527 PWM Controller ICs
Introduction
The ISL6526 and the ISL6527 provide power control and
protection for applications requiring low voltage and high
power. Both ICs can be biased from voltages between 3.3V
and 5V. The ISL6526 and ISL6527 contain a high
performance error amplifier, a high accuracy reference, a
fixed 300kHz or 600kHz internal oscillator, over-current
protection circuitry, and two MOSFET drivers for use in
synchronous-rectified buck converters. Both the ISL6526
and the ISL6527 are capable of regulating the output voltage
while the DC-DC converter is sinking current. The ISL6527
also allows for an external reference to be used. All these
features are packaged in a small 14-lead SOIC or a 16-lead
5x5[mm] MLFP. More complete descriptions of the ISL6526
and the ISL6527 can be found in their respective
datasheets [1, 2].
This application note details the ISL6526 and ISL6527 in
DC-DC converters for applications requiring a tightly
regulated, fixed output voltage. Low-cost applications
requiring a DC-DC converter can benefit from one of the
designs presented in this application note
ISL6526/27 Reference Designs
The ISL6526/27 evaluation board highlights the operation of
the ISL6526 and ISL6527 ICs in an embedded application.
There are five evaluation boards from which to choose.
The ISL6526EVAL1 board is built with the ISL6526CB and
shipped with an ISL6526ACB sample piece. Evaluation of
the ISL6526CB can be performed immediately. If evaluation
of the ISL6526ACB is desired, then it is a simple matter of
replacing the controller. The ISL6527EVAL1 is shipped with
the ISL6527CB and shipped with an ISL6527ACB sample
piece. As with the ISL6526CB and ISL6526ACB, the parts
are interchangeable.
The ISL6526EVAL2 and ISL6527EVAL2 are ready for
evaluation without any modifications.
All evaluation boards have the same output filter,
compensation components and MOSFETs. They are
configured for an output of 2.5V with a maximum load of 5A.
The ISL6526 evaluation boards have a fixed output while the
ISL6527 evaluation boards allow the use of a potentiometer
to adjust the output voltage from 0.75V to 3.0V. Unless
otherwise noted, this application note assumes that the
output of the ISL6527 evaluation board is 2.5V.
Quick Start Evaluation
The evaluation board is shipped ‘ready to use’ right from the
box. The board accepts a range of input voltages from 3.3V
to 5V from a standard power supply. The output can be
exercised through an external load.
There are posts available on the board for introducing power
to the board and also for drawing current from the regulated
output. Three probe points are also available for use. These
probe points provide Kelvin connections to the
CPVOUT(TP3) and CT1(TP1) pins on both the ISL6526 and
ISL6527. The ENABLE pin on the ISL6526 and the REF_IN
pin on the ISL6527 can be probed from TP2.
Recommended Test Equipment
To test the functionality of the ISL6526 or ISL6527, the
following equipment is recommended:
- An adjustable 0 - 5V, 5A capable bench power supply
- An electronic load
- Four channel oscilloscope with probes
- Precision digital multimeter
Power and Load Connections
There are 2 sets of terminals that are used to supply the
input voltage and load the output.
INPUT VOLTAGE
Connect the positive lead of the adjustable bench power
supply to the 3.3V post (J1). Connect the ground lead of
the supply to GND post (J2).
OUTPUT LOADING - SOURCING CURRENT
Connect the positive terminal of the load to the VOUT
post (J3). Connect the return terminal of the same load to
the GND post (J4).
OUTPUT LOADING - SINKING CURRENT
CAUTION: The return terminal of the load must float for
this to work properly.
Table 1 - Evaluation Boards
Board Name
Switching
Frequency
IC
Package
ISL6526EVAL1
300kHz
and
600kHz
ISL6526CB
ISL6526ACB
14 ld SOIC
ISL6526EVAL2
300kHz
ISL6526CR
16 ld MLFP
ISL6527EVAL1
300kHz
and
600kHz
ISL6527CB
ISL6527ACB
14 ld SOIC
ISL6527EVAL2
600kHz
ISL6527ACR
16 ld MLFP
June 2002
Application Note
