USER’S MANUAL
ISL6406EVAL1, ISL6406EVAL2, ISL6406EVAL3
PWM Controller Evaluation Boards
AN1031
Rev 1.00
July 9, 2008
Introduction
The ISL6406, ISL6426 is a highly efficient, adjustable
frequency, synchronous buck switching regulator optimized
for generating lower voltages for the distributed DC/DC
architecture required for DSP, memory and core
communication processors in Broadband Gateway
applications. The ISL6406 offers an adjustable output
voltage, while the ISL6426 provides a fixed 1.8V output.
The wide programmable switching frequency range of
100kHz to 700kHz allows the use of small surface mount
inductors and capacitors. The device also provides external
frequency synchronization making it an ideal choice for
DC/DC converter applications. This combination of features
and the available miniature packaging enables the design of
a high performance power supply in an extremely small PCB
area, ideal for portable instruments, access devices and
other applications requiring high efficiency.
There are two MOSFET drivers for use in
synchronous-rectified Buck converters. The ISL6406 is
capable of regulating the output voltage while the DC/DC
converter is sinking current. All these features are packaged
in a 16 lead SOIC, a thin shrunk 16 lead TSSOP or a 16 lead
4x4[mm] QFN (MLFP). More complete descriptions of the
ISL6406 can be found in the data sheet [1].
This application note details the use of the ISL6406 in
DC-DC converter applications requiring a tightly regulated,
fixed output voltage. Any low-cost application requiring a
DC/DC converter can benefit from one of the designs
presented in this application note.
Quick Start Evaluation
The evaluation board is shipped “ready to use” right from the
box. The board accepts a 3.3V input from a standard power
supply. The output can be exercised through the use of an
external load.
There are posts available on the board for introducing power
to the board and for drawing current from the regulated
output. Two probe points are also available, which provide
kelvin connections to CPVOUT (TP1) and CT1 (P6).
The SYNC/EN pin may be probed from P5.
Recommended Test Equipment
- An adjustable 0V to 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 for supplying the
input voltage and loading the output.
Input Voltage
- Connect the positive lead of the adjustable
bench power supply to the 3.3V post (P1). Connect the
ground lead of the supply to the GND post (P2).
Output Loading, Sourcing Current
- Connect the positive
terminal of the electronic load to the VOUT post (P3).
Connect the return terminal of the same load to the GND
post (P4).
Start-up
There are two distinct start-up methods for the ISL6406
regulator. The first method is invoked through the application
of power to the IC. The soft-start feature allows for a
controlled turn-on of the output once the Power On Reset
(POR) threshold of the input voltage has been reached.
Figure 1 (on the next page) shows the start-up profile of the
regulator in relation to the start-up of the 3.3V input supply
and the bias supply generated by the charge pump.
The second method of start-up is through the use of the
Enable/Shutdown feature. Holding the SYNC/EN pin on the
ISL6406, ISL6426 below 0.8V will disable the regulator by
forcing both the upper and lower MOSFETs off. Releasing
the pin allows the regulator to start up.
ISL6406, ISL6426 Reference Designs
The ISL6406, ISL6426 evaluation board highlights the
operation of the IC in an embedded application. There are
three evaluation boards from which to choose.
TABLE 1. EVALUATION BOARDS
BOARD NAME
ISL6406EVAL1
ISL6406EVAL2
ISL6406EVAL3
IC
ISL6406/26CV
ISL6406/26CR
ISL6406/26CB
PACKAGE
16 Ld TSSOP
16 Ld QFN
16 Ld SOIC
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 evaluation board is built with the ISL6406 and is shipped
with ISL6426 samples. Evaluation of the ISL6426 may be
performed by replacing the ISL6406.
AN1031 Rev 1.00
July 9, 2008
Page 1 of 12
ISL6406EVAL1, ISL6406EVAL2, ISL6406EVAL3
Shutdown
V
CPVOUT
1V/DIV
V
VCC
1V/DIV
As discussed in the previous section, if the SYNC/EN (P5)
pin is pulled down and held below 0.8V, the regulator will be
turned off. Figure 2 shows the shutdown profile of the
regulator with no load applied. Figure 3 shows the shutdown
of the regulator under full load.
Output Performance
All three evaluation boards have the same schematic and
are designed to provide a 2.5V/5A output. The switching
frequency is set at 300kHz, which can be adjusted from
100kHz to 700kHz using a resistor, R5, connected to the RT
pin.
900
800
FREQUENCY (kHz)
700
600
500
400
300
200
100
V
OUT
1V/DIV
2ms/DIV
FIGURE 1. START-UP FROM POR
V
OUT
500mV/DIV
200 180 150 130 100 80 64.5 50 44.5 39
RT (k)
0
33 26.4 22
FIGURE 4. RT vs FREQUENCY
V
ENABLE
500mV/DIV
500ms/DIV
FIGURE 2. SHUTDOWN WITH NO LOAD (ISL6406)
The ISL6406, ISL6426 can be synchronized to an external
frequency by connecting an external clock source to
SYNC/EN (P5). The external sync clock may range from
100kHz to well over 750kHz.
Figure 5 shows the ripple voltage on the output of the
regulator.
V
OUT
at 300kHz
10mV/DIV
V
ENABLE
1V/DIV
V
OUT
1V/DIV
V
OUT
at 600kHz
10mV/DIV
20µs/DIV
FIGURE 3. SHUTDOWN WITH FULL LOAD (ISL6406)
5µs/DIV
FIGURE 5. OUTPUT RIPPLE VOLTAGE
AN1031 Rev 1.00
July 9, 2008
Page 2 of 12
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