19-3480; Rev 1; 8/05
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 24V
♦
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
MAX8727
The MAX8727 is a high-performance step-up DC-DC
converter that provides a regulated supply voltage for
active-matrix thin-film transistor (TFT) liquid-crystal dis-
plays (LCDs). The MAX8727 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 24V from an input voltage
between 2.6V and 5.5V. Soft-start slowly ramps the input
current and is programmed with an external capacitor.
The MAX8727 is available in a 10-pin thin DFN package.
Ordering Information
Applications
Notebook Computer Displays
LCD Monitor Panels
PART
MAX8727ETB
MAX8727ETB+
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
10 Thin DFN 3mm x 3mm
10 Thin DFN 3mm x 3mm
+Denotes
lead-free package.
Pin Configuration
V
IN
2.6V TO 5.5V
TOP VIEW
Minimal Operating Circuit
V
OUT
6
LX
1
2
3
4
5
10
9
SS
FREQ
IN
LX
LX
9
3
FREQ
SHDN
8
IN
7
LX
FB
2
COMP
FB
SHDN
GND
GND
MAX8727
GND 5
GND
4
MAX8727
8
7
6
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
MAX8727
ABSOLUTE MAXIMUM RATINGS
LX to GND ..............................................................-0.3V to +26V
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 Thin DFN (derate 24.4mW/°C above +70°C) ....1951mW
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, FREQ = GND,
T
A
= 0°C to +85°C.
Typical values are at T
A
= +25°C, unless otherwise noted.) (Note 1)
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
Shutdown FB Input Voltage
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
LX
= 24V
0.11
V
FB
= 1V, 75% duty cycle
3.0
3.8
125
30
0.21
4.6
250
45
0.31
A
Ω
µA
V/A
FREQ = GND
FREQ = IN
540
1000
87
640
1220
90
740
1500
93
kHz
%
SHDN
= GND
0.05
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
700
0.10
0.15
1.26
250
0.15
300
V
nA
%/V
µS
V/V
V
V
IN
rising, typical hysteresis is 50mV
V
FB
= 1.3V, not switching
V
FB
= 1.0V, switching
SHDN
= GND
2.20
2.38
0.225
2
0.1
V
OUT
< 18V
18V < V
OUT
< 24V
CONDITIONS
MIN
2.6
4.0
TYP
MAX
5.5
5.5
24
2.57
0.440
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, FREQ = GND,
T
A
= 0°C to +85°C.
Typical values are at T
A
= +25°C, unless otherwise noted.) (Note 1)
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
×
V
IN
0.1
×
V
IN
6.0
0.001
9.5
1
0.3
×
V
IN
V
V
V
µA
µA
CONDITIONS
MIN
TYP
MAX
UNITS
MAX8727
ELECTRICAL CHARACTERISTICS
(V
IN
= V
SHDN
= 3V, FREQ = GND,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 1)
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
Shutdown FB Input Voltage
OSCILLATOR
Frequency
Maximum Duty Cycle
n-CHANNEL MOSFET
Current Limit
On-Resistance
Current-Sense Transresistance
SOFT-START
Reset Switch Resistance
Charge Current
V
SS
= 1.2V
2.5
100
7.5
Ω
µA
0.11
V
FB
= 1V, 75% duty cycle
3.0
5.1
250
0.31
A
mΩ
V/A
FREQ = GND
FREQ = IN
490
900
86
770
1600
94
kHz
%
SHDN
= GND
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
0.05
1.215
1.260
250
0.15
300
0.15
V
nA
%/V
µS
V
V
IN
rising, typical hysteresis is 50mV
V
FB
= 1.3V, not switching
V
FB
= 1.0V, switching
SHDN
= GND
2.20
V
OUT
< 18V
18V < V
OUT
< 24V
CONDITIONS
MIN
2.6
4.0
TYP
MAX
5.5
5.5
24
2.57
0.44
5
10
UNITS
V
V
V
mA
µA
_______________________________________________________________________________________
3
TFT-LCD Step-Up DC-DC Converter
MAX8727
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= V
SHDN
= 3V, FREQ = GND,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 1)
PARAMETER
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
×
V
IN
0.3
×
V
IN
V
V
CONDITIONS
MIN
TYP
MAX
UNITS
Note 1:
Specifications to -40°C are guaranteed by design, not production tested.
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)
MAX8727 toc01
EFFICIENCY vs. LOAD CURRENT
(640kHz OPERATION)
MAX8727 toc02
LOAD REGULATION
MAX8727 toc03
100
L = 3.6μH
90
EFFICIENCY (%)
100
L = 6.8μH
90
EFFICIENCY (%)
0.5
0
LOAD REGULATION (%)
80
V
IN
= 5.0V
70
V
IN
= 3.3V
80
V
IN
= 5.0V
70
V
IN
= 3.3V
-0.5
V
IN
= 5.0V
V
IN
= 3.3V
-1.0
60
60
-1.5
50
1
10
100
1000
LOAD CURRENT (mA)
50
1
10
100
1000
LOAD CURRENT (mA)
-2.0
1
10
100
1000
LOAD CURRENT (mA)
SWITCHING FREQUENCY
vs. INPUT VOLTAGE
MAX8727 toc04
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX8727 toc05
SUPPLY CURRENT vs. TEMPERATURE
(SWITCHING)
MAX8727 toc06
1400
1300
SWITCHING FREQUENCY (kHz)
1200
1100
1000
900
800
700
600
500
2.5
3.0
3.5
4.0
4.5
5.0
FREQ = GND
FREQ = IN
4.0
3.5
SUPPLY CURRENT (mA)
3.0
2.5
2.0
1.5
1.0
0.5
0
NONSWITCHING
SWITCHING
5
4
SUPPLY CURRENT (mA)
V
IN
= 5.0V
3
V
IN
= 3.3V
2
1
0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
-40
-20
0
20
40
60
80
100
SUPPLY VOLTAGE (V)
TEMPERATURE (°C)
5.5
INPUT VOLTAGE (V)
4
_______________________________________________________________________________________
TFT-LCD Step-Up DC-DC Converter
MAX8727
Typical Operating Characteristics (continued)
(Circuit of Figure 1. V
IN
= 5V, V
MAIN
= 15V, T
A
= +25°C unless otherwise noted.)
SOFT-START
(R
LOAD
= 30Ω)
MAX8727 toc07
LOAD-TRANSIENT RESPONSE
(I
LOAD
= 50mA TO 550mA)
MAX8727 toc08
V
OUT
5V/div
OV
INDUCTOR
CURRENT
1A/div
OA
15V
V
OUT
5mV/div
AC-COUPLED
I
OUT
500mA/div
50mA
INDUCTOR
CURRENT
1A/div
OA
1ms/div
1μs/div
PULSED LOAD-TRANSIENT RESPONSE
(I
LOAD
= 100mA TO 1.1A)
MAX8727 toc09
SWITCHING WAVEFORMS
(I
LOAD
= 600mA)
MAX8727 toc10
15V
V
OUT
5mV/div
AC-COUPLED
I
OUT
1A/div
0.1A
INDUCTOR
CURRENT
1A/div
OA
LX
10V/div
OV
INDUCTOR
CURRENT
1A/div
OA
1μs/div
1μs/div
_______________________________________________________________________________________
5
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