19-3833; Rev 0; 9/05
MAX8728 Evaluation Kit
General Description
The MAX8728 evaluation kit (EV kit) is a fully assembled
and tested surface-mount circuit board that provides the
voltages and features required for active-matrix thin-film
transistor (TFT), liquid-crystal display (LCD) panels in
LCD monitors and LCD TVs. The EV kit contains a step-
down switching regulator, a step-up switching regulator,
a positive two-stage charge pump for the TFT gate-on
supply, and a negative single-stage charge pump for
the TFT gate-off supply. Also included is a logic-con-
trolled, high-voltage switch with adjustable delay, and
a capacitive dummy load at the gate-on supply for ease
of testing.
The EV kit, as configured, provides the following out-
puts from a +10VDC to +13.2VDC power supply. The
step-down switching regulator is configured for a +3.3V
output, providing at least 2A. The step-up switching
regulator is configured for a +13.5V output, providing at
least 500mA. The positive charge pump is configured
for a +28V output, providing at least 50mA. The nega-
tive charge pump is configured for a -6V output, provid-
ing at least 150mA. The high-voltage switch can be
controlled by external logic and can be configured for a
delay set by an external capacitor.
The MAX8728 switches at 1.5MHz, allowing the use of
tiny surface-mount components. The EV kit can also
operate at a lower frequency with component changes.
The MAX8728 TQFN package (0.8mm maximum
height) with low-profile external components allows this
circuit to be less than 2mm high.
♦
Output Voltages
+3.3V Output at 2A (Step-Down Switching
Regulator)
+13.5V Output at 500mA (Step-Up Switching
Regulator)
+28V Output at 50mA (Positive Charge Pump)
-6V Output at 150mA (Negative Charge Pump)
♦
Resistor-Adjustable Switching Regulator and
Charge-Pump Output Voltages
♦
Logic-Controlled, High-Voltage Switch with
Adjustable Delay
♦
Selectable 500kHz/1MHz/1.5MHz Switching
Frequency
♦
180° Out-of-Phase Switching
♦
Low-Profile, Surface-Mount Components
♦
Fully Assembled and Tested
Features
♦
Configured for +10V to +13.2V Input Range
Evaluates: MAX8728
Ordering Information
PART
MAX8728EVKIT
TEMP RANGE
0°C to +70°C*
IC PACKAGE
32 TQFN-EP**
*This
limited temperature range is for the EV kit PC board only.
The MAX8728 IC temperature range is -40°C to +85°C.
**EP
= Exposed paddle.
Component List
DESIGNATION
C1
QTY
1
DESCRIPTION
1µF
±10%,
10V X5R ceramic
capacitor (0603)
TDK C1608X5R1A105K
0.22µF
±20%,
16V X7R ceramic
capacitors (0603)
TDK C1608X7R1C224M
10µF
±20%,
16V X5R ceramic
capacitors (1206)
TDK C3216X5R1C106M
0.01µF
±10%,
50V X7R ceramic
capacitor (0603)
TDK C1608X7R1H103K
22µF
±20%,
6.3V X7R ceramic
capacitor (1206)
TDK C3216X7R0J226M
DESIGNATION
C10, C11, C14,
C19–C22
QTY
7
DESCRIPTION
0.1µF
±10%,
50V X7R ceramic
capacitors (0603)
TDK C1608X7R1H104K
47pF
±5%,
50V C0G ceramic
capacitor (0603)
TDK C1608C0G1H470J
10µF
±20%,
6.3V X5R ceramic
capacitor (0805)
TDK C2012X5R0J106M
100pF
±5%,
50V C0G ceramic
capacitor (0603)
TDK C1608C0G1H101J
C2, C13
2
C12
1
C3–C7
5
C15
1
C8
1
C16
1
C9
1
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
MAX8728 Evaluation Kit
Evaluates: MAX8728
Component List (continued)
DESIGNATION
C17
QTY
1
DESCRIPTION
220pF
±10%,
50V X7R ceramic
capacitor (0603)
TDK C1608X7R1H221K
1µF
±10%,
50V X7R ceramic
capacitor (1206)
TDK C3216X7R1H105K
1500pF
±10%,
50V X7R ceramic
capacitor (0603)
TDK C1608X7R1H152K
1000pF
±5%,
50V C0G ceramic
capacitor (0603)
TDK C1608C0G1H102J
Not installed, capacitors (1206)
Not installed, capacitor (0603)
10pF
±5%,
50V C0G ceramic
capacitor (0603)
TDK C1608C0G1H100J
3A, 30V Schottky diodes (M-flat)
Toshiba CMS02
250mA, 75V high-speed silicon
diode (SOD-523)
Central Semiconductor CMOD4448
220mA, 100V dual diodes (SOT23)
Fairchild MMBD4148SE
2-pin headers
3-pin headers
DESIGNATION
JU6
L1
C18
1
L2
QTY
0
1
1
DESCRIPTION
Not installed three-way jumper
(four pins)
6.4µH, 1.5ADC inductor
Sumida CDRH6D12-6R4
2.6µH, 2.6ADC inductor
Sumida CDRH6D12-2R6
2.4A, -20V p-channel MOSFET
(3-pin SuperSOT)
Fairchild FDN304P
6.49kΩ
±1%
resistor (0805)
10kΩ
±1%
resistors (0805)
100kΩ
±5%
resistors (0805)
10Ω
±5%
resistor (0805)
44.2kΩ
±1%
resistor (0805)
158kΩ
±1%
resistor (0805)
115kΩ
±1%
resistor (0805)
20kΩ
±1%
resistor (0805)
160kΩ
±5%
resistor (0805)
127kΩ
±1%
resistor (0805)
22.1kΩ
±1%
resistors (0805)
2kΩ
±5%
resistor (0805)
287kΩ
±1%
resistor (0805)
MAX8728ETJ+ (32-pin TQFN-EP
5mm x 5mm x 0.8mm)
Shunts
MAX8728 EV kit PC board
C23
1
P1
R1
R2, R16
R3, R10
R4
R5
R6
R7
R8
R9
R11
R12, R15
R13
R14
U1
—
—
1
1
2
2
1
1
1
1
1
1
1
2
1
1
1
5
1
C24
C25, C26
C27
C28
1
0
0
1
D1, D2
2
D3
1
D4, D5, D6
JU1, JU3
JU2, JU4, JU5
3
2
3
Component Suppliers
SUPPLIER
Central Semiconductor
Fairchild Semiconductor
Sumida
TDK
Toshiba
PHONE
631-435-1110
888-522-5372
847-545-6700
847-803-6100
949-455-2000
WEBSITE
www.centralsemi.com
www.fairchildsemi.com
www.sumida.com
www.component.tdk.com
www.toshiba.com/taec
Note:
Indicate that you are using the MAX8728 when contacting these component suppliers.
2
_______________________________________________________________________________________
MAX8728 Evaluation Kit
Quick Start
Recommended Equipment
•
•
+10V to +13.2V, 2A DC power supply
One voltmeter
The EV kit is configured for a 1.5MHz switching frequency.
Operation at 500kHz or 1MHz is possible, but requires
component changes. See the
Switching Frequency
Selection (FSEL)
section.
As configured, the step-down switching regulator
(OUT1) generates a +3.3V output and can provide at
least 2A. The step-down switching-regulator output
voltage can be adjusted from 2V to 3.6V by replacing
feedback resistors R1 and R2. Refer to the
Detailed
Description, Step-Down Regulator
section in the
MAX8728 data sheet.
The step-up switching regulator (AVDD) generates a
+13.5V output and can provide at least 500mA. The
step-up switching-regulator output voltage can be
adjusted from V
IN
to +28V by replacing feedback resis-
tors R7 and R8. Refer to the
Design Procedure, Step-
Up Regulator Design, Output-Voltage Selection
section
in the MAX8728 data sheet. Operation at significantly
higher output voltages can reduce the available output
current, and may require changes in component values
or component voltage ratings.
The gate-on (VSRC) supply consists of two positive
charge-pump stages to generate +28V and can pro-
vide greater than 50mA. This output can be adjusted
from approximately V
IN
to nearly 3 x V
IN
by replacing
feedback resistors R14 and R15. Refer to the
Design
Procedure, Charge-Pump Regulators, Output-Voltage
Selection
section in the MAX8728 data sheet.
The positive charge-pump regulator’s startup delay
time can be adjusted by replacing capacitor C11. Refer
to the
Positive Charge-Pump Regulator
and
Power-Up
Sequence
sections in the MAX8728 data sheet for
additional details.
The VGOFF supply consists of a single negative
charge-pump stage to generate -6V and can provide
greater than 150mA. This output can be adjusted from
approximately 0 to -V
IN
by replacing feedback resistors
R5 and R6. Refer to the
Design Procedure, Charge-
Pump Regulators, Output-Voltage Selection
section in
the MAX8728 data sheet.
The MAX8728 contains two high-voltage switches that
operate in a complementary fashion. One of the switches
provides a connection between the SRC and GON
pins. The other switch provides a connection between
the GON and DRN pins. Both switches can be con-
trolled by an external TTL square-wave signal connected
to the CTL pad.
When CTL is high, GON is connected to SRC, charging
GON to the voltage of the positive charge pump at the
VSRC pad. When CTL is low, GON may be connected
to DRN, allowing GON to discharge toward AVDD
3
Evaluates: MAX8728
The MAX8728 EV kit is fully assembled and tested.
Follow these steps to verify board operation.
Do not
turn on the power supply until all connections are
completed:
1) Verify that a shunt is installed across jumper JU1
(EV kit ON).
2) Verify that a shunt is installed across pins 1 and 2 of
jumper JU2 (enables step-up, charge pumps, and
switch-control block).
3) Verify that no shunt is installed across jumper JU3
(no capacitive dummy load C23).
4) Verify that a shunt is installed across pins 1 and 2 of
jumper JU4 (VGON discharges toward AVDD).
5) Verify that a shunt is installed across pins 1 and 2 of
jumper JU5 (high-voltage, switch-control block set
to mode 1).
6) Preset the power supply to +12V and disable the
output.
7) Connect the positive terminal of the power supply to
the VIN pad on the EV kit. Connect the negative ter-
minal of the power supply to the PGND pad next to
the VIN pad.
8) Turn on the power supply.
9) Verify that the step-down switching regulator output
(OUT1) is +3.3V.
10) Verify that the step-up switching regulator output
(AVDD) is +13.5V.
11) Verify that the gate-on supply (VSRC) is +28V.
12) Verify that the gate-off supply (VGOFF) is -6V.
Detailed Description
The MAX8728 EV kit contains a step-down switching
regulator, a step-up switching regulator, a positive two-
stage charge pump, a negative single-stage charge
pump, and a high-voltage switch matrix. The MAX8728
switching frequency is configured for 1.5MHz. The EV
kit is configured to operate from a +10VDC to
+13.2VDC power supply that can provide at least 2A.
Operation below +10V (down to +7V) is possible, but
requires changes in component values, charge-pump
configurations, output voltages and currents, or other
parameters. Refer to the MAX8728 IC data sheet for
additional information.
_______________________________________________________________________________________
MAX8728 Evaluation Kit
Evaluates: MAX8728
(through resistor R13, jumper JU4, and diode D3) or
toward PGND (through resistor R13 and jumper JU4).
However, GON stops discharging when the voltage at
GON drops to 10 times the threshold voltage set at the
THR pin. As configured, the voltage at the THR pin is
set to 2V by voltage-divider resistors R11 and R12.
The high-voltage switches have two modes of operation
controlled by jumper JU5. The first mode has no delay,
while the second mode has an adjustable delay fea-
ture. In the first mode, GON is switched to SRC at the
rising edge of the control signal connected to the CTL
pad, and then switched to DRN at the falling edge of
the control signal. In the second mode, GON is
switched to SRC at the rising edge of the control signal.
However, at the falling edge of the control signal, GON
is not switched to DRN until the voltage at the MODE
pin reaches 0.5 x V
REF
. Refer to the
Detailed
Description, High-Voltage Switch Control
section in the
MAX8728 data sheet for additional details.
Table 1. JU1 Jumper Selection (SHDN)
SHUNT POSITION
Installed
(default)
Not installed
Not installed
(external logic
controller
connected to
SHDN
pad)
SHDN
PIN
CONNECTED TO
VL
GND
(through resistor
R3)
EV KIT
FUNCTION
Enabled
Shutdown mode
SHDN
driven by
external logic
controller,
shutdown is
active low
External logic
controller
Jumper Selection
Shutdown Mode (
SHDN
)
Jumper JU1 controls the shutdown pin (SHDN) of the
MAX8728 IC. The shutdown pin can also be controlled
by an external logic controller connected to the EV kit
SHDN
pad. Remove the shunt from jumper JU1 before
connecting an external controller to the
SHDN
pad. See
Table 1 for shunt positions.
and the step-down regulator operates in its power-saving
skip mode.
On the rising edge of EN, the step-down regulator
enters its fixed-frequency mode, and the step-up,
charge pumps and switch matrix begin their startup
sequence (refer to the
Power-Up Sequence
section in
the MAX8728 IC data sheet).
The EN pin includes a 5µA current source, which,
together with capacitor C10 from EN to ground, can
provide a startup delay for the above blocks.
Jumper JU2 controls the enable pin (EN) of the
MAX8728 IC. The enable pin can also be controlled by
an external logic controller connected to the EV kit’s EN
pad. Remove the shunt from jumper JU2 before connect-
ing an external controller to the EN pad. See Table 2 for
shunt positions.
Enable Input (EN)
The MAX8728 EV kit features an enable input (EN).
When EN is low, the step-up regulator, the positive
charge-pump regulator, the negative charge-pump regu-
lator, and the high-voltage switch matrix are disabled
Table 2. Jumper JU2 Functions (EN)
SHUNT
LOCATION
EN PIN
CONNECTED TO
DELAY
EV KIT’S
STEP-DOWN
REGULATOR
Fixed-frequency
mode (after delay)
Skip mode
Fixed-frequency
mode
Controlled by
external logic
controller
EV KIT’S STEP-UP REGULATOR,
POSITIVE AND NEGATIVE CHARGE-
PUMP REGULATORS,
HIGH-VOLTAGE SWITCH
Enabled (after delay)
Disabled
Enabled
1-2
(default)
2-3
Not installed
Not installed
(external logic
controller connected
to EN pad)
C10
GND
Unconnected; pulled
high internally
Set by C10
—
No delay
External logic controller
No delay
Controlled by external logic controller
4
_______________________________________________________________________________________
MAX8728 Evaluation Kit
Dummy Load for the High-Voltage Switch
Output (VGON)
The MAX8728 EV kit features a capacitive dummy load
of 1500pF (C23) at the VGON output pad to simulate a
panel load to test the switch matrix. Jumper JU3
selects and deselects the dummy load. Table 3 lists
jumper JU3 options.
Evaluates: MAX8728
Table 5. Jumper JU5 Functions (MODE)
SHUNT
LOCATION
1-2
(default)
2-3
Not installed
MODE PIN
CONNECTED TO
REF
(through resistor
R16)
C17
Unconnected
HIGH-VOLTAGE
SWITCH MODE
No delay
Delay set by C17
Not allowed
Table 3. Jumper JU3 Functions (LOAD)
SHUNT
LOCATION
Installed
Not installed
(default)
DUMMY LOAD
(C23)
Connected to
VGON
Unconnected
EV KIT
FUNCTION
Testing mode
(no panel)
Normal operation
(panel load)
Switching Frequency Selection (FSEL)
The step-down and step-up regulators on the MAX8728
EV kit switch at the same frequency, but are 180
degrees out-of-phase with each other. The MAX8728
switching frequency is selectable among 1.5MHz,
1MHz, and 500kHz by jumper JU6. Table 6 lists the
selectable JU6 jumper options.
VGON Discharge Path
The MAX8728 EV kit features a method to configure the
VGON discharge path using resistor R13 and jumper
JU4. When CTL is low, GON may be connected to DRN,
allowing VGON to discharge through resistor R13. R13
can be connected to AVDD (through diode D3) or to
PGND using jumper JU4. Table 4 lists the selectable
JU4 jumper options. If VGON’s desired lower level is
greater than AVDD, discharge VGON toward AVDD to
save power. The VGON’s discharge rate can be adjust-
ed by selecting a different value for R13.
Table 6. Jumper JU6 Functions (FSEL)
SHORT
LOCATION
1-4
(shorted, default)
1-3
1-2
FSEL PIN
CONNECTED TO
GND
REF
VL
EV KIT
FREQUENCY
1.5MHz
500kHz
1MHz
Table 4. Jumper JU4 Functions
(VGON Discharge)
SHUNT
LOCATION
1-2
(default)
2-3
DRN PIN
CONNECTED TO
AVDD
through resistor
R13 and diode D3
PGND through
resistor R13
VGON DISCHARGED
TOWARD
AVDD
PGND
Note that jumper JU6 is not installed and is shorted
between pin holes 1 and 4 by a PC board trace. To uti-
lize jumper JU6, cut open the PC board trace between
pin holes 1 and 4, and install a shorting wire between
pin holes 1 and 2 for 1MHz operation, or pin holes 1
and 3 for 500kHz operation.
The EV kit is configured for 1.5MHz operation. Optimum
performance at lower frequencies requires larger
inductor values. Refer to the
Step-Down Regulator
Design and Step-Up Regulator Design
section in the
MAX8728 data sheet.
Output Voltage Selection
High-Voltage Switch Mode (MODE)
The MAX8728 EV kit features an option to select the
operating mode (delay or no delay) for the high-voltage
switches, on the rising edge of the CTL pin, GON con-
nects to SRC. On CTL's falling edge, GON may con-
nect immediately to DRN (no delay), or GON may con-
nect to DRN after a delay set by C17. Jumper JU5
selects the high-voltage switch operating mode for the
MAX8728. Table 5 lists the selectable JU5 jumper
options.
Step-Down Switching-Regulator Output
Voltage (OUT1)
The MAX8728 EV kit’s step-down switching regulator’s
output (OUT1) is set to +3.3V by feedback resistors R1
and R2. To generate output voltages other than +3.3V
(from 2V to 3.6V), select different external voltage-
divider resistors, R1 and R2. Refer to the
Detailed
Description, Step-Down Regulator
section in the
MAX8728 data sheet for instructions on selecting resis-
tors R1 and R2.
5
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