19-1000; Rev 2; 11/09
MAX8785A Evaluation Kit
General Description
The MAX8785A evaluation kit (EV kit) is an assembled
and tested PCB that demonstrates the MAX8785A full-
bridge cold-cathode fluorescent lamp (CCFL) controller
for piezoelectric transformer-based back light power
supplies. Lamp brightness is adjustable by an on-
board potentiometer.
♦
+8V to +25V Input Range
♦
Brightness Adjustable by an On-Board
Potentiometer
♦
10:1 Digital Pulse-Width Modulation (DPWM)
♦
Strike Voltage Up to 2kV
♦
Fully Assembled and Tested
Features
Evaluates: MAX8785A
Ordering Information
PART
MAX8785AEVKIT#
TYPE
EV Kit
#Denotes
RoHS compliant.
Component List
DESIGNATION
C1
QTY
1
DESCRIPTION
10µF ±20%, 25V X5R ceramic
capacitor (1206)
TDK C3216X5R1E106M
1µF ±20%, 10V X5R ceramic
capacitors (0603)
AVX 0603ZD105MAT
TDK C1608X5R1A105M
6800pF ±10%, 50V X7R ceramic
capacitor (0603)
KEMET C0603C682K5RAC
TDK C1608X7R1H682K
0.22µF ±10%, 6.3V X5R ceramic
capacitor (0402)
Murata GRM155R60J224K
Taiyo Yuden JMK105BJ224KV
TDK C1005X5R0J224M
0.22µF ±10%, 25V X5R ceramic
capacitor (0603)
Murata GRM188R61E224KA
TDK C1608X5R1E224K
0.047µF ±10%, 16V X7R ceramic
capacitor (0402)
Murata GRM155R71C473K
TDK C1005X7R1C473K
DESIGNATION
QTY
DESCRIPTION
0.1µF ±10%, 10V X5R ceramic
capacitors (0402)
Murata GRP155R61A104K
Taiyo Yuden LMK105BJ104KV
TDK C1005X5R1A104K
0.047µF ±10%, 50V X7R ceramic
capacitor (0603)
Murata GRM188R71H473K
TDK C1608X7R1H473K
1000pF ±10%, 50V X7R ceramic
capacitor (0603)
KEMET C0603C102K5RAC
TDK C1608X7R1H102K
Not installed, ceramic capacitors
(0402)
Shrouded header for CCFL lamp
connection, 3.5mm pin spacing,
PCB mount
3.6V zener diode (SOD-523)
Central CMOZ3V6 lead free
2A, 32V fuse (1206)
Cooper 3216FF2-R
Digi-Key 283-2544-1-ND
C8, C9, C10
3
C2, C4
2
C11
1
C3
1
C12
1
C5
1
C13, C14
0
CN1
1
C6
1
D1
1
C7
1
F1
1
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
MAX8785A Evaluation Kit
Evaluates: MAX8785A
Component List (continued)
DESIGNATION
GL1, GL2, VFB,
IFB
JU1
L1
QTY
0
1
1
DESCRIPTION
Not installed, test points
2-pin header
27µH, 0.8A inductor
TOKO D73F 636FY-270M
30V 2.5A dual n-channel
MOSFET (6-pin SOT23)
Fairchild FDC6561AN
(Top Mark: 561)
Not installed, dual n-channel
MOSFET (8-pin SO)
Fairchild FDS6912A
105kΩ ±1% resistor (0603)
100kΩ ±5% resistors (0402)
100kΩ ±5% resistor (0603)
150kΩ ±1% resistor (0603)
150Ω ±1% resistor (0603)
280kΩ ±5% resistor (0603)
200kΩ ±1% resistors (0805)
1.54kΩ ±1% resistor (0603)
100kΩ potentiometer (multiturn),
3/8in
2
—
1
—
1
U1
1
T1
1
DESIGNATION
R18
R19
R20
R21
R22
R23
R24
R25
R26
QTY
0
0
0
0
1
1
1
0
0
DESCRIPTION
Not installed, resistor (0603)
Not installed, shorted by PC trace
(0402)
Not installed, shorted by PC trace
(0603)
Not installed, resistor (0402)
1kΩ ±5% resistor (0603)
1MΩ ±5% resistor (0402)
10Ω ±5% resistor (0603)
Not installed, shorted by PC trace
(0603)
Not installed, resistor (0402)
4.5W, 50kHz ±1.5kHz
piezoelectric transformer
TOKIN HT320628-21(2.5)CB
Full-bridge controller for
piezoelectric transformers
(28 TQFN-EP*)
MAX8785AETI+
Shunt
PCB: MAX8785A EVALUATION
KIT#
N1A/B, N2A/B
2
N3A/B, N4A/B
R1
R2, R3, R4
R5
R6
R7
R8
R9–R15
R16
R17
0
1
3
1
1
1
1
7
1
1
*EP
= Exposed pad.
Component Suppliers
SUPPLIER
AVX Corporation
Central Semiconductor Corp.
Digi-Key Corp.
Fairchild Semiconductor
KEMET Corp.
Murata Electronics North America, Inc.
NEC TOKIN America, Inc.
Taiyo Yuden
TDK Corp.
TOKO America, Inc.
PHONE
843-946-0238
631-435-1110
800-344-4539
888-522-5372
864-963-6300
770-436-1300
408-324-1790
800-348-2496
847-803-6100
847-297-0070
www.avxcorp.com
www.centralsemi.com
www.digikey.com
www.fairchildsemi.com
www.kemet.com
www.murata-northamerica.com
www.nec-tokinamerica.com
www.t-yuden.com
www.component.tdk.com
www.tokoam.com
WEBSITE
Note:
Indicate that you are using the MAX8785A when contacting these component suppliers.
2
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MAX8785A Evaluation Kit
Quick Start
•
•
Shutdown
A shunt installed on JU1 enables the MAX8785A EV kit.
To set the MAX8785A to shutdown mode, remove the
shunt on JU1.
Evaluates: MAX8785A
Recommended Equipment
A DC power supply capable of supplying a voltage
between +8V to +25V at 2A to power the MAX8785A
board
A CCFL lamp with the following specifications:
Maximum RMS strike voltage
≤
2kV
RMS lamp current = 6mA
Input power
≤
4W
Dimming Control
The MAX8785A EV kit sets the MAX8785A with analog
dimming-control mode. The brightness of the lamp is
adjustable by turning potentiometer R17.
To set the EV kit to external digital dimming-control
mode, cut open the trace shorting R20 pad, then install
a 0Ω resistor on R18 (or short R18 pad). Connect an
external signal to LSYNC pad. Refer to the
External
Digital (DPWM) Control
section in the MAX8785A IC
data sheet for more detail.
Procedure
The MAX8785A EV kit is fully assembled and tested.
Follow the steps below to verify board operation.
Warning:
High voltage is present on this evaluation kit.
Do not turn on power until all connections are made.
1) Connect the lamp to the connector CN1.
2) Connect the +8V and +25V supply to the pads
labeled IN and GND on the MAX8785A EV kit.
3) Turn on the power supply.
4) Enable the MAX8785A by installing the shunt on JU1.
Setting the Lamp Current
The MAX8785A EV kit sets the default lamp current with
6mA. To set the lamp current other than 6mA, select R7
as follows:
R7 = (π x 800mV)/(2√
2
x I
LAMP (RMS)
)
Refer to the
Setting the Lamp Current
section in the
MAX8785A IC data sheet for more detail.
Detailed Description
The MAX8785A EV kit demonstrates the MAX8785A full-
bridge cold-cathode fluorescent lamp (CCFL) controller
for piezoelectric transformer-based back light power sup-
plies. The MAX8785A guarantees lamp striking by
sweeping the switching frequency from high to low until
the lamp is struck. The MAX8785A achieves 10:1 dim-
ming range using either analog or digital dimming control.
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3
MAX8785A Evaluation Kit
Evaluates: MAX8785A
Figure 1. MAX8785A EV Kit Schematic
4
_______________________________________________________________________________________
MAX8785A Evaluation Kit
Evaluates: MAX8785A
Figure 2. MAX8785A EV Kit Component Placement Guide—Component Side
Figure 3. MAX8785A EV Kit PCB Layout—Component Side
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