USER GUIDES

ISL6841EVAL3Z Evaluation Board for General
Purpose Industrial Applications
®
Application Note
February 12, 2008
AN1384.0
Choice of PWM Controller
Target Design Specifications
The ISL684x family of devices are superior performing pin
compatible replacements for the industry standard 384x
single-ended current mode PWM controllers. Also available
in 8 Ld MSOP and 8 Ld SOIC, the ISL6841 in the space
saving 2mmx3mm DFN package is used in the
ISL6841EVAL3Z evaluation board.
The following design requirements were targeted for
evaluation purposes:
• Switching Frequency, fsw: 200kHz.
• VIN: 18VDC to 30VDC.
• VOUT: 12V with 5% absolute regulation.
The design requirements of this application require the
superior performance characteristics of the ISL6841. Some
key features of this part include:
• POUT: 30W.
• Tight internal voltage reference of 1%.
• Full Load Efficiency: 80% minimum under all line
conditions, and loads of 20% and above.
• 40ns peak current sensing.
• Ripple: 1% of output voltage.
• Internal 1A MOSFET driver.
• Form Factor: 2”x2”.
The ISL6841 was selected for its UVLO threshold and its
50% maximum duty cycle limit. In addition, its low UVLO
start threshold would help in easily modifying the design in
catering to lower input voltage applications.
The detailed design procedure for a continuous mode
flyback topology has been discussed in the application note
AN1192, available on Intersil’s website:
• IOUT: 2.5A.
http://www.intersil.com/data/an/an1192.pdf
Topology Selection
This evaluation board was designed to allow for maximum
flexibility, targeting applications that use a typical battery
input of 24V. Given the low input voltages for this application,
a single-ended topology would be ideal. The flyback
topology was selected for the low power levels targeted by
this application with emphasis on low BOM cost. Continuous
conduction mode of operation was chosen to achieve higher
efficiencies at the expense of lower bandwidth of operation,
a direct consequence of transition from continuous to
discontinuous mode of operation.
For feature-rich applications that need short-circuit
protection, over-temperature shutdown, etc., the ISL6841
may be substituted with the ISL6721. This evaluation board
has been provided with placeholders for primary auxiliary
winding feedback to save component cost in case of
applications that can tolerate loose regulation requirements.
Typical Performance Characteristics
The major performance criterion for the converter are
efficiency, load regulation and low output ripple. As can be
observed from the following figures, the 20% load efficiency
target of 80% has been comfortably met under all input
voltage conditions. Tight load regulation has been achieved
by using the opto-coupled feedback scheme.
Waveforms
Typical waveforms can be found in the following Figures.
Figure 1 shows the efficiency curves at different input
voltages. Figure 2 shows the worst case output voltage
ripple and noise.
Figures 3 through 6 show the drain and gate waveforms of
the primary FET under different input and loading conditions.
Figures 7 through 10 show the secondary rectifier
waveforms under different input and loading conditions.
A measure of the stability can be determined from the Bode
plots shown in Figures 11 through 14. As shown, the gain
and phase margins under the extreme conditions of line and
load indicate a stable system under all operating conditions.
.
1
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. 2008. All Rights Reserved
All other trademarks mentioned are the property of their respective owners.
Application Note 1384
100
18V
24V
90
EFFICIENCY (%)
80
70
30V
60
50
40
30
20
10
0
0
0.25 0.50
0.75 1.00 1.25 1.50 1.75
OUTPUT CURRENT
2.00 2.25 2.50
FIGURE 1. EFFICIENCY PLOTS
FIGURE 2. OUTPUT RIPPLE AND NOISE, 20MHz BW
FIGURE 4. FET VOLTAGES, VIN = 30V, LOAD = 250mA
2
FIGURE 3. FET VOLTAGES, VIN = 18V, LOAD = 250mA
FIGURE 5. FET VOLTAGES, VIN = 18V, LOAD = 2.5A
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February 12, 2008
Application Note 1384
FIGURE 6. FET VOLTAGES, VIN = 30V, LOAD = 2.5A
FIGURE 8. RECTIFIER WAVEFORM, VIN = 30V,
LOAD = 250mA
FIGURE 7. RECTIFIER WAVEFORM, VIN = 18V,
LOAD = 250mA
FIGURE 9. RECTIFIER WAVEFORM, VIN = 18V, LOAD = 2.5A
FIGURE 10. RECTIFIER WAVEFORM, VIN = 30V, LOAD = 2.5A
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Application Note 1384
FIGURE 11. STABILITY ANALYSIS, VIN = 18V, FULL LOAD
FIGURE 12. STABILITY ANALYSIS, VIN = 18V, NO LOAD
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Application Note 1384
FIGURE 13. STABILITY ANALYSIS, VIN = 30V, FULL LOAD
FIGURE 14. STABILITY ANALYSIS, VIN = 30V, NO LOAD
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ISL6841EVAL3Z Schematic
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Application Note 1384
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February 12, 2008
Application Note 1384
.
2.000
Circuit Elements
Input Filtering Capacitance – C1, C3
Isolation Transformer – T1
Power MOSFET – Q1
Current Sense Network – T2, D2, R4, R3, C8 (R5 optional)
1.845
Start-up Bias Circuit – R10, Q2, D6
Operating Bias Circuit – D5, R7, C9, D7
Control Circuit – U1, C10, C11, R11, C12, R6
Conventional Rectification Diode – D3
Output Filtering – C5, C6, C2
FIGURE 15. TOP VIEW - ISL6841EVAL3Z BOARD
Feedback Network – R13, R14, R15, R16, R17, R18, R19,
R20, R21, D8, D9, C15, C16, U2
Slope Compensation - Q3, R22
2.000
Primary RCD Snubber - R1, D1, C4
Primary FET Snubber - R23, C18
Secondary Rectifier Snubber - R2, C7
Safety Capacitor - C17
1.845
Optional Circuit for Primary Auxiliary Feedback - R8, R9,
R12, C13, C14
Summary
ISL6841
FIGURE 16. BOTTOM VIEW - ISL6841EVAL3Z BOARD
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Using a high performance, low-cost PWM controller with a
low pin-count, all the design targets have been achieved,
while keeping the cost to a minimum. The ISL6841EVAL3Z
schematic and BOM for the evaluation board are provided
as follows. Please contact our Technical Support Center for
custom output voltage requirements. They can be reached
through Intersil’s website at:
http://www.intersil.com/cda/home/ or via phone at
1-888-INTERSIL.
AN1384.0
February 12, 2008
Application Note 1384
t
Component List
REFERENCE
DESIGNATOR
C1
VENDOR
Panasonic
PART NUMBER
EEE-FK1H151P
DESCRIPTION
CAP, SMD, 10.3mm, 150µF, 50V, 20%, ROHS, ALUM.ELEC.
C2, C6
TDK/Murata
CAP, SMD, 1210, 22µF, 16V, 20%, X7R, ROHS
C3
TDK/Murata
CAP, SMD, 1206, 1µF, 50V, 10%, X7R, ROHS
C4
TDK/Murata
CAP, SMD, 0805, 0.01µF, 100V, 10%, X7R, ROHS
C5
Sanyo
16SVP180M
CAP, SMD, E12, 180µF, 16V, 20%, OSCON, ROHS
C7, C18
TDK/Murata
CAP, SMD, 0805, 820pF, 100V, 5%, NPO, ROHS
C8, C12
TDK/Murata
CAP, SMD, 0402, 220pF, 50V, 5%, NPO, ROHS
C9
TDK/Murata
CAP, SMD, 0805,1.0µF, 25V, 10%, X7R, ROHS
C10, C11
TDK/Murata
CAP, SMD, 0402, 0.1µF, 16V, 10%, X7R, ROHS
C15
TDK/Murata
CAP, SMD, 0402, 150pF, 50V, 5%, NPO, ROHS
C16
TDK/Murata
CAP, SMD, 0603, 0.22µF, 16V, 10%, X7R, ROHS
C17
Murata
GA352QR7GF152KW01L CAP, SMD, 2220, 1500pF, 250V, 10%, X7R, ROHS
D1
Diodes
B340LB-13-F
DIODE-SCHOTTKY, SMD, SMB, 2P, 40V, 3A LOW VF, ROHS
D2, D5
Diodes
BAS70T-7-F
DIODE-SCHOTTKY, SMD, SOT-523, 70V, 70mA, ROHS
D3
Diodes
PDS560-13
DIODE-RECTIFIER, SMD, POWER DI5, 3P, 60V, 5A, ROHS
D6, D9
Diodes
BZT52C10T-7
DIODE-ZENER, SMD, SOD-523, 10V, 150mW, ROHS
D7
Diodes
BAT54CT-7-F
DIODE-SCHOTTKY, SMD, SOT-523, 30V, 200mA, DUAL DIODE,
ROHS
D8
Sipex
SPX431LM-L
IC-ADJ. PREC.SHUNT REGULATOR, 3P, SOT-23, ROHS
Q1
International Rectifier IRF6646
TRANSISTOR-MOS, N-CHANNEL, SMD, DIRECTFET-MN, 80V,
12A, ROHS
Q2
Diodes
BCX55-16
TRANSISTOR, NPN, SMD, SOT-89, 4P, 60V, 1A, ROHS
Q3
On Semi
MMBT2222ALT1G-T
TRANSISTOR, NPN, 3LD, SOT23, 40V, 600mA, ROHS
R1
RES, SMD, 2512, 3.01k, 1W, 1%, TF, ROHS
R2, R23
RES, SMD, 2512, 20Ω, 1W, 5%, TF, ROHS
R3
RES, SMD, 0402, 249Ω, 1/16W, 1%, TF, ROHS
R4
RES-CURR.SENSE, SMD, 1206, 6.49Ω, 1/4W, 1%, ROHS
R5
RES, SMD, 2512, 0Ω, 1W, TF, ROHS
R6
RES, SMD, 0402, 10Ω, 1/16W, 1%, TF, ROHS
R7
RES, SMD, 0402, 100Ω, 1/16W, 1%, TF, ROHS
R10
RES, SMD, 0402, 30k, 1/16W, 5%, TF, ROHS
R11
RES, SMD, 0402, 17.8k, 1/16W, 1%, TF, ROHS
R13, R14
RES, SMD, 0402, 100k, 1/16W, 1%, TF, ROHS
R15
RES, SMD, 0402, 5.11k, 1/16W, 1%, TF, ROHS
R16
RES, SMD, 0402, 499Ω, 1/16W, 1%, TF, ROHS
R17
RES, SMD, 0402, 4.64k, 1/16W, 1%, TF, ROHS
R18
RES, SMD, 0402, 1k, 1/16W, 1%, TF, ROHS
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Application Note 1384
Component List (Continued)
REFERENCE
DESIGNATOR
VENDOR
PART NUMBER
R19, R22
DESCRIPTION
RES, SMD, 0402, 10k, 1/16W, 1%, TF, ROHS
R20
RES, SMD, 0402, 6.34k, 1/16W, 1%, TF, ROHS
R21
RES, SMD, 0402, 3.83k, 1/16W, 1%, TF, ROHS
T1
TDK
DCT20EFD-U42S004
TRANSFORMER-FLYBACK, SMD, 20µH, CUSTOM, ROHS
T2
Pulse
P8205NL
TRANSFORMER-CURRENT SENSE, SMD, 8P, 500µH, 10A,
ROHS
U1
Intersil
ISL6841IRZ
IC-CURRENT MODE PWM CONTROLLER, 8P, DFN, 2x3, ROHS
U2
California Eastern
Laboratories
PS2801-1-A
IC-PHOTOCOUPLER, 4P, SSOP, ROHS
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February 12, 2008
Application Note 1384
Layout
The ISL6841EVAL3Z board met the form factor target with
room to spare. Following are the layout pictures of the board.
The gerber files are available upon request.
FIGURE 17. SILKSCREEN - TOP LAYER
FIGURE 18. SILKSCREEN - BOTTOM LAYER
FIGURE 19. ETCH - TOP LAYER
FIGURE 20. ETCH - LAYER 2
FIGURE 21. ETCH - LAYER 3
FIGURE 22. ETCH - 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
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