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IT
TION K
VALUA
E
BLE
AVAILA
TFT-LCD Step-Up DC-DC Converter
General Description
Features
♦
90% Efficiency
♦
Adjustable Output from V
IN
to 28V
♦
2.6V to 5.5V Input Supply Range
♦
Input Supply Undervoltage Lockout
♦
Pin-Programmable 640kHz/1.2MHz Switching
Frequency
♦
Programmable Soft-Start
♦
0.1µA Shutdown Current
♦
Small, 10-Pin Thin DFN Package
MAX8740
The MAX8740 is a high-performance, step-up DC-DC
converter that provides a regulated supply voltage for
active-matrix, thin-film transistor (TFT), liquid-crystal
displays (LCDs). The MAX8740 incorporates current-
mode, fixed-frequency, pulse-width modulation (PWM)
circuitry with a built-in n-channel power MOSFET to
achieve high efficiency and fast transient response.
Users can select 640kHz or 1.2MHz operation using a
logic input pin (FREQ). The high switching frequencies
allow the use of ultra-small inductors and low-ESR
ceramic capacitors. The current-mode architecture pro-
vides fast transient response to pulsed loads. A com-
pensation pin (COMP) gives users flexibility in adjusting
loop dynamics. The 30V internal MOSFET can generate
output voltages up to 28V from a 2.6V and 5.5V input
voltage range. Soft-start slowly ramps the input current
and is programmed with an external capacitor.
The MAX8740 is available in a 10-pin thin DFN package.
Applications
Notebook Computer Displays
LCD Monitor Panels
PART
MAX8740ETB
Ordering Information
TEMP RANGE
-40°C to +85°C
PIN-PACKAGE
10 TDFN 3mm x 3mm
Pin Configuration
V
IN
2.6V TO 5.5V
FREQ
SS
LX
LX
IN
Minimal Operating Circuit
V
OUT
TOP VIEW
10
9
8
7
6
8
IN
6
LX
7
LX
FB
2
MAX8740
MAX8740
9
3
FREQ
SHDN
GND 5
GND
4
1
COMP
2
FB
3
SHDN
4
GND
5
GND
10
SS
COMP 1
THIN DFN
3mm x 3mm
________________________________________________________________
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.
TFT-LCD Step-Up DC-DC Converter
MAX8740
ABSOLUTE MAXIMUM RATINGS
LX to GND ..............................................................-0.3V to +30V
IN,
SHDN,
FREQ, FB to GND ...................................-0.3V to +6V
COMP, SS to GND .......................................-0.3V to (V
IN
+ 0.3V)
LX Switch Maximum Continuous RMS Current .....................2.4A
Continuous Power Dissipation (T
A
= +70°C)
10-Pin TDFN (derate 24.1mW/°C above +70°C) .......1481.5mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-65°C to +160°C
Lead Temperature (soldering, 10s) .................................+300°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(V
IN
= V
SHDN
= 3V,
T
A
= 0°C to +85°C.
Typical values are at T
A
= +25°C, unless otherwise noted.)
PARAMETER
Input Voltage Range
Output Voltage Range
IN Undervoltage-Lockout
Threshold
IN Quiescent Current
IN Shutdown Current
ERROR AMPLIFIER
FB Regulation Voltage
FB Input Bias Current
FB Line Regulation
Transconductance
Voltage Gain
OSCILLATOR
Frequency
Maximum Duty Cycle
n-CHANNEL MOSFET
Current Limit
On-Resistance
Leakage Current
Current-Sense Transresistance
SOFT-START
Reset Switch Resistance
Charge Current
V
SS
= 1.2V
2.5
4.5
100
7.5
Ω
µA
V
FB
= 1V, 71% duty cycle
V
IN
= 3V (typ value at T
A
= +25°C)
V
IN
= 5V (typ value at T
A
= +25°C)
V
LX
= 28V
0.09
3.9
4.6
0.11
0.095
30
0.15
5.3
0.17
0.15
55
0.25
A
Ω
µA
V/A
FREQ = GND
FREQ = IN
540
1000
88
640
1220
91
740
1500
94
kHz
%
Level to produce V
COMP
= 1.24V
V
FB
= 1.24V
Level to produce V
COMP
= 1.24V, V
IN
= 2.6V to 5.5V
100
1.22
50
1.24
125
0.05
200
2400
1.26
250
0.15
315
V
nA
%/V
µS
V/V
V
IN
rising, typical hysteresis is 50mV; LX remains off
below this level
V
FB
= 1.3V, not switching
V
FB
= 1.0V, switching, FREQ = GND
SHDN
= GND
2.20
2.38
0.22
2
0.1
V
OUT
< 18V
18V < V
OUT
< 24V
CONDITIONS
MIN
2.6
4.0
TYP
MAX
5.5
5.5
28
2.57
0.44
5
10.0
UNITS
V
V
V
mA
µA
2
_______________________________________________________________________________________
TFT-LCD Step-Up DC-DC Converter
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= V
SHDN
= 3V,
T
A
= 0°C to +85°C.
Typical values are at T
A
= +25°C, unless otherwise noted.)
PARAMETER
CONTROL INPUTS
SHDN,
FREQ Input Low Voltage
SHDN,
FREQ Input High Voltage
SHDN,
FREQ Input Hysteresis
FREQ Pulldown Current
SHDN
Input Current
SHDN
= GND
V
IN
= 2.6V to 5.5V
V
IN
= 2.6V to 5.5V
V
IN
= 2.6V to 5.5V
2.3
0.7 x
V
IN
0.1 x
V
IN
6.0
0.001
9.5
1
0.3 x
V
IN
V
V
V
µA
µA
CONDITIONS
MIN
TYP
MAX
UNITS
MAX8740
ELECTRICAL CHARACTERISTICS
(V
IN
= V
SHDN
= 3V,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 1)
PARAMETER
Input Voltage Range
Output Voltage Range
IN Quiescent Current
IN Shutdown Current
ERROR AMPLIFIER
FB Regulation Voltage
FB Line Regulation
Transconductance
OSCILLATOR
Frequency
n-CHANNEL MOSFET
Current Limit
Current-Sense Transresistance
CONTROL INPUTS
SHDN,
FREQ Input Low Voltage
SHDN,
FREQ Input High Voltage
V
IN
= 2.6V to 5.5V
V
IN
= 2.6V to 5.5V
0.7 x
V
IN
0.3 x
V
IN
V
V
V
FB
= 1V, 71% duty cycle
3.9
0.09
5.3
0.25
A
V/A
FREQ = GND
FREQ = IN
490
900
770
1600
kHz
Level to produce V
COMP
= 1.24V
Level to produce V
COMP
= 1.24V, V
IN
= 2.6V to 5.5V
100
1.215
1.260
0.15
330
V
%/V
µS
V
FB
= 1.3V, not switching
V
FB
= 1.0V, switching, FREQ = GND
SHDN
= GND
V
OUT
< 18V
18V < V
OUT
< 28V
CONDITIONS
MIN
2.6
4.0
TYP
MAX
5.5
5.5
28
0.44
5
10
UNITS
V
V
mA
µA
Note 1:
-40°C specifications are guaranteed by design, not production tested.
_______________________________________________________________________________________
3
TFT-LCD Step-Up DC-DC Converter
MAX8740
Typical Operating Characteristics
(Circuit of Figure 1. V
IN
= 5V, V
MAIN
= 15V, T
A
= +25°C, unless otherwise noted.)
EFFICIENCY vs. LOAD CURRENT
(1.2MHz OPERATION)
MAX8740 toc01
EFFICIENCY vs. LOAD CURRENT
L = 5.6µH
f
OSC
= 640kHz
MAX8740 toc02
OUTPUT VOLTAGE vs. LOAD CURRENT
12.9
12.7
OUTPUT VOLTAGE (V)
12.5
12.3
12.1
11.9
11.7
11.5
f
OSC
= 1.2MHz
L = 2.7µH
V
IN
= 3.3V
V
IN
= 5.0V
MAX8740 toc03
100
90
EFFICIENCY (%)
80
70
60
50
40
1
L = 2.7µH
f
OSC
= 1.2MHz
100
90
EFFICIENCY (%)
80
70
60
50
40
1
V
IN
= 5.0V
V
IN
= 5.0V
V
IN
= 3.3V
V
IN
= 3.3V
10
100
1000
10
100
1000
1
10
LOAD CURRENT (mA)
LOAD CURRENT (mA)
100
1000
LOAD CURRENT (mA)
10,000
SWITCHING FREQUENCY
vs. INPUT VOLTAGE
MAX8740 toc04
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX8740 toc05
SUPPLY CURRENT vs. TEMPERATURE
(SWITCHING)
MAX8740 toc06
1400
0.7
0.6
SUPPLY CURRENT (mA)
0.5
0.4
0.3
0.2
0.1
NONSWITCHING
0.60
SWITCHING FREQUENCY (kHz)
1200
SUPPLY CURRENT (mA)
FREQ = IN
SWITCHING
V
IN
= 5.0V
0.55
V
IN
= 3.3V
0.50
1000
800
FREQ = GND
600
400
2.5
3.0
3.5
4.0
4.5
INPUT VOLTAGE (V)
5.0
5.5
0.45
2.5
3.0
3.5
4.0
4.5
SUPPLY VOLTAGE (V)
5.0
5.5
-40
-20
0
20
40
60
TEMPERATURE (°C)
80
100
SOFT-START
(R
LOAD
= 30Ω)
MAX8740 toc07
SWITCHING WAVEFORMS
(I
LOAD
= 800mA)
MAX8740 toc08
2ms/div
400ns/div
4
_______________________________________________________________________________________
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