an1031

Using the ISL6406, ISL6426 PWM Controller
Evaluation Boards
®
Application Note
July 9, 2008
AN1031.1
Introduction
Quick Start Evaluation
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 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.
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 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
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].
Power and Load Connections
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.
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).
ISL6406, ISL6426 Reference Designs
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 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
IC
PACKAGE
ISL6406EVAL1
ISL6406/26CV
16 Ld TSSOP
ISL6406EVAL2
ISL6406/26CR
16 Ld QFN
ISL6406EVAL3
ISL6406/26CB
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.
1
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).
Start-up
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.
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
1-888-INTERSIL or 1-888-468-3774 | Intersil (and design) is a registered trademark of Intersil Americas Inc.
Copyright Intersil Americas Inc. 2003, 2008. All Rights Reserved
All other trademarks mentioned are the property of their respective owners.
Application Note 1031
Shutdown
VCPVOUT
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.
VVCC
Output Performance
1V/DIV
VOUT
1V/DIV
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.
2ms/DIV
900
FIGURE 1. START-UP FROM POR
700
600
500
400
300
200
FREQUENCY (kHz)
800
100
VOUT
500mV/DIV
200 180 150 130 100 80 64.5 50 44.5 39
0
33 26.4 22
RT (kΩ)
FIGURE 4. RT vs FREQUENCY
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.
VENABLE
500mV/DIV
500ms/DIV
FIGURE 2. SHUTDOWN WITH NO LOAD (ISL6406)
Figure 5 shows the ripple voltage on the output of the
regulator.
VOUT at 300kHz
10mV/DIV
VOUT
1V/DIV
VENABLE
1V/DIV
VOUT at 600kHz
10mV/DIV
20µs/DIV
5µs/DIV
FIGURE 3. SHUTDOWN WITH FULL LOAD (ISL6406)
2
FIGURE 5. OUTPUT RIPPLE VOLTAGE
AN1031.1
July 9, 2008
Application Note 1031
Conclusion
References
Compact and highly efficient regulators can be easily
implemented with the ISL6406 and ISL6426. The IC offers
high-performance features with a small footprint, which
makes it ideal for many low-voltage DC/DC power solutions.
For Intersil documents available on the web, see
http://www.intersil.com/
[1] ISL6406, ISL6426 Data Sheet, Intersil Corporation, File
No. FN9073.
Evaluation Board Schematic
NOTE: All evaluation boards share the same schematic.
3.3V
P1
C1A
C3
GND
P2
5
C4
6
R6
7
C2
U1
13
P6
VCC
OCSET
CT1
4
R1
TP1
CT2
CPVOUT
RT
3
D1
C5
12
CPGND
1
GND
BOOT
ISL6406
ISL6426
C7
UGATE
10
R7
C6
15
VOUT
PHASE
16
L1
2.5V @ 5A
14
P3
P5
8
SYNC/EN
LGATE
COMP
C8A-B
2
Q1
FB
9
11
C10
R3
R2
GND
C11
R4
C9
JP1
P4
R5
NOTE: Remove R3, R4, C9, and R5 from the board for ISL6426 evaluation.
3
AN1031.1
July 9, 2008
Application Note 1031
Bill of Materials
TABLE 2. EVALUATION BOARD SPECIFIC BILL OF MATERIALS
REFERENCE
QTY
PART NUMBER
PART TYPE
DESCRIPTION
PACKAGE
VENDOR
ISL6406EVAL1
U1
1
ISL6406CV
IC
Synchronous Buck PWM Controller
16 Lead
TSSOP
Intersil
1
ISL6426CV
IC
Synchronous Buck PWM Controller
16 Lead
TSSOP
Intersil
1
ISL6406CR
IC
Synchronous Buck PWM Controller
16 Lead
4x4 QFN
Intersil
1
ISL6426CR
IC
Synchronous Buck PWM Controller
16 Lead
4x4 QFN
Intersil
1
ISL6406CB
IC
Synchronous Buck PWM Controller
16 Lead
SOIC
Intersil
1
ISL6426CB
IC
Synchronous Buck PWM Controller
16 Lead
SOIC
Intersil
ISL6426EVAL1
U1
ISL6406EVAL2
U1
ISL6426EVAL2
U1
ISL6406EVAL3
U1
ISL6426EVAL3
U1
4
AN1031.1
July 9, 2008
Application Note 1031
Bill of Materials
TABLE 3. EVALUATION BOARD COMMON BILL OF MATERIALS
REFERENCE
Q1
QTY
1
PART NUMBER
PART TYPE
ITF86110DK8T
Dual MOSFET
FDS6912A
Alternate Part
DESCRIPTION
PACKAGE
VENDOR
N-channel, 30V, 6A, 0.028Ω
SOIC-8
Fairchild
D1
1
MMSD4148T1
Diode
100V, 300mA
SOD123
ON-Semi
L1
1
ETQP6F1R0SFA
Inductor
1.0µH, 30%, 14.2A
SMD
Panasonic ETQ-P
series
C1A, C1B,
C8A, C8B
4
EEF-UE0J151R
Capacitor, Alu. Elec.
150µF, 20%, 6.3V, 0.015Ω
SMD
SP_CAP_UE
Panasonic
C2
1
08053C102KAT2A
Capacitor, Ceramic
1000pF, 10%, 25V
SM_0805
AVX
C3, C7
2
08053C104MAT2A
Capacitor, Ceramic
0.1µF, 20%, 25V
SM_0805
AVX
C4
1
08053C224MAT2A
Capacitor, Ceramic
0.22µF, 20%, 25V
SM_0805
AVX
C5
1
1210YD106KAT2A
Capacitor, Ceramic
10µF, 10%, 16V
SM_0805
AVX
C6
1
08053C105MAT2A
Capacitor, Ceramic
1µF, 20%, 25V
SM_0805
AVX
C9
1
08053C822MAT2A
Capacitor, Ceramic
8200pF, 20%, 25V
SM_0805
AVX
C10
1
08053A033KAT2A
Capacitor, Ceramic,
NPO
33pF, 10%, 25V
SM_0805
AVX
C11
1
08053C562MAT2A
Capacitor, Ceramic
5600pF, 20%, 25V
SM_0805
AVX
CAPACITORS
RESISTORS
R1
1
Resistor, Film
9.76k, 1%, 1/10 Watt
SM_0805
Panasonic
R2
1
Resistor, Film
6.49k, 1%, 1/10 Watt
SM_0805
Panasonic
R3
1
Resistor, Film
2.26k, 1%, 1/10 Watt
SM_0805
Panasonic
R4
1
Resistor, Film
124, 1%, 1/10 Watt
SM_0805
Panasonic
R5
1
Resistor, Film
1.07k, 1%, 1/10 Watt
SM_0805
Panasonic
R6
1
Resistor, Film
64.9k, 1%, 1/10 Watt
SM_0805
Panasonic
R7
1
Resistor, Film
100k, 1%, 1/10 Watt
SM_0805
Panasonic
OTHERS
SP1
1
131-5031-00
Terminal, Scope Probe Terminal, Scope Probe
P1 - P6
6
1514-2
Turrett Post
Terminal post, through hole, 1/4
inch tall
PTH
Keystone
TP1
1
5002
TEST POINT vertical,
white
PC test jack
PTH
Keystone
JP1
1
68000-236-1X2
Header
1X2 Break Strip GOLD
JP1
1
S9001-ND
Jumper
2 pin jumper
4
Tektronix
Digikey
Bumpers
5
AN1031.1
July 9, 2008
Application Note 1031
ISL6406, ISL6426 EVAL1 Layers
FIGURE 6. ISL6406EVAL1 - TOP SILK PRINT
FIGURE 7. ISL6406EVAL1 - TOP LAYER
FIGURE 8. ISL6406EVAL1 - LAYER 2
6
AN1031.1
July 9, 2008
Application Note 1031
ISL6406, ISL6426 EVAL1 Layers (Continued)
FIGURE 9. ISL6406EVAL1 - LAYER 3
FIGURE 10. ISL6406EVAL1 - LAYER 4
FIGURE 11. ISL6406EVAL1 - BOTTOM LAYER
7
AN1031.1
July 9, 2008
Application Note 1031
ISL6406, ISL6426 EVAL2 Layers
FIGURE 12. ISL6406EVAL2 - TOP SILK PRINT
FIGURE 13. ISL6406EVAL2 - TOP LAYER
FIGURE 14. ISL6406EVAL2 - LAYER 2
8
AN1031.1
July 9, 2008
Application Note 1031
ISL6406, ISL6426 EVAL2 Layers (Continued)
FIGURE 15. ISL6406EVAL2 - LAYER 3
FIGURE 16. ISL6406EVAL2 - LAYER 4
FIGURE 17. ISL6406EVAL2 - BOTTOM LAYER
9
AN1031.1
July 9, 2008
Application Note 1031
ISL6406, ISL6426 EVAL3 Layers
FIGURE 18. ISL6406EVAL3 - TOP SILK PRINT
FIGURE 19. ISL6406EVAL3 - TOP LAYER
FIGURE 20. ISL6406EVAL3 - LAYER 2
10
AN1031.1
July 9, 2008
Application Note 1031
ISL6406, ISL6426 EVAL3 Layers (Continued)
FIGURE 21. ISL6406EVAL3 - LAYER 3
FIGURE 22. ISL6406EVAL3 - LAYER 4
FIGURE 23. ISL6406EVAL3 - BOTTOM LAYER
Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without notice. Accordingly, the reader is cautioned to
verify that the Application Note or Technical Brief is current before proceeding.
For information regarding Intersil Corporation and its products, see www.intersil.com
11
AN1031.1
July 9, 2008