19-0971; Rev 1; 6/08
Internal-Switch Boost Regulator with
Integrated 3-Channel Scan Driver for TFT LCDs
General Description
The MAX8798 includes a high-performance, step-up
regulator; a high-speed operational amplifier; a digitally
adjustable VCOM calibration device with nonvolatile
memory; an I
2
C interface; and a high-voltage, level-shift-
ing scan driver. The device is optimized for thin-film
transistor (TFT) liquid-crystal display (LCD) applications.
The step-up DC-DC converter provides the regulated
supply voltage for panel source driver ICs. The high
switching frequency allows the use of ultra-small induc-
tors and ceramic capacitors. The current-mode control
architecture provides fast transient response to pulsed
loads typical of source driver loads. The step-up regu-
lator features soft-start and current limit.
The high-current operational amplifier is designed to
drive the LCD backplane (VCOM). The amplifier fea-
tures high output current (±150mA), fast slew rate
(45V/µs), wide bandwidth (20MHz), and rail-to-rail
inputs and outputs.
The programmable VCOM calibrator is externally
attached to the VCOM amplifier’s resistive voltage-divider
and sinks a programmable current to adjust the VCOM
output-voltage level. An internal 7-bit digital-to-analog
converter (DAC) controls the sink current. The DAC is
ratiometric relative to BOOST and is guaranteed to be
monotonic over all operating conditions. The calibrator IC
includes an EEPROM to store the desired VCOM voltage
level. The 2-wire I
2
C interface between the LCD panel
and the programming circuit minimizes panel connector
lead count and simplifies production equipment.
The high-voltage, level-shifting scan driver is designed
to drive the TFT panel gate drivers. Its three outputs
swing 65V (maximum) between +45V (maximum) and
-25V (minimum) and can swiftly drive capacitive loads.
To save power, the two complementary outputs are
designed to allow charge sharing during state changes.
The MAX8798 is available in a 36-pin, thin QFN pack-
age with a maximum thickness of 0.8mm for ultra-thin
LCD panels.
KIT
ATION
EVALU
E
BL
AVAILA
Features
♦
1.8V to 5.5V IN Supply Voltage Range
♦
1.8V to 4.0V V
DD
Input Voltage Range
♦
1.2MHz Current-Mode Step-Up Regulator
Fast Transient Response
Built-In 20V, 1.9A, 150mΩ MOSFET
♦
High-Speed (20MHz) Operational Amplifier
±150mA Output Current
♦
High-Voltage Drivers with Scan Logic
+45V to -25V Outputs
65V (maximum) Swing
Output Charge Sharing
♦
Programmable VCOM Calibrator
7-Bit Adjustable Current-Sink Output
I
2
C Interface
EEPROM Setting Memory
♦
Thermal-Overload Protection
MAX8798
Simplified Operating Circuit
VN
VP
V
IN
V
MAIN
50kΩ
SHDN
IN
LX
DISH
1kΩ
CPV
SYSTEM
OE
STV
OECON
SCAN DRIVER
LOGIC
AND
GATE DRIVERS
1.9A
STEP-UP
REG
PGND
FB
COMP
AGND
GON
BOOST
NEG
VN
GOFF
STVP
CKVCS
VP
PANEL
CKVB
CKVBCS
VCOM
TO VCOM
BACKPLANE
Applications
Notebook Computer Displays
LCD Monitor Panels
VIN
CKV
VL
V
DD
3.3V
LINEAR
REG
VCOM CALIBRATOR
7
POS
BGND
OUT
GND
Ordering Information
PART
TEMP RANGE
PIN-
PACKAGE
36 Thin QFN
6mm x 6mm
PKG
CODE
T-3666M-1
I
2
C
BUS
SDA
SCL
SCLS
WPP
WPN
SET
MAX8798ETX+ -40°C to +85°C
________________________________________________________________
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.
Internal-Switch Boost Regulator with
Integrated 3-Channel Scan Driver for TFT LCDs
MAX8798
ABSOLUTE MAXIMUM RATINGS
IN, VL,
SHDN
to AGND .........................................-0.3V to +7.5V
V
DD
, SDA, SCL, SCLS, WPN, WPP, SET to GND...-0.3V to +4.0V
OECON, CPV, OE, STV to AGND..........................-0.3V to +4.0V
COMP, FB to AGND ......................................-0.3V to (V
L
+ 0.3V)
DISH to GND ............................................................-6V to +2.0V
LX to PGND ............................................................-0.3V to +20V
OUT, VCOM, NEG, POS to BGND........-0.3V to (BOOST + 0.3V)
PGND, BGND, AGND to GND...............................-0.3V to +0.3V
GON to AGND ........................................................-0.3V to +50V
GOFF to AGND .............................................-30V to (V
IN
+ 0.3V)
GON to GOFF ......................................................................+70V
BOOST to BGND ....................................................-0.3V to +20V
CKV, CKVB, STVP, CKVCS,
CKVBCS to AGND..................(GOFF - 0.3V) to (GON + 0.3V)
LX, PGND RMS Current Rating.............................................2.4A
Continuous Power Dissipation (T
A
= +70°C)
NiPd Lead Frame with Nonconductive Epoxy
36-Pin, 6mm x 6mm Thin QFN
(derate 27.2mW/°C above +70°C) .........................2179.8mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-65°C to +150°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
DD
= V
SHDN
= +3V, circuit of Figure 2, V
BOOST
= 8V, V
GON
= 23V, V
GOFF
= -12V, V
POS
= 0, V
NEG
= 1.5V, V
OE
= V
CPV
=
V
STV
= V
OECON
= 0,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
V
DD
Input Voltage Range
V
DD
Quiescent Current
V
DD
Undervoltage Lockout
IN Input Voltage Range
IN Quiescent Current
IN Undervoltage Lockout
Thermal Shutdown
VL Output Voltage
VL Undervoltage Lockout
VL Maximum Output Current
MAIN DC-DC CONVERTER
BOOST Supply Current
Operating Frequency
Oscillator Maximum Duty Cycle
FB Regulation Voltage
FB Load Regulation
FB Line Regulation
FB Input Bias Current
FB Transconductance
FB Voltage Gain
FB Fault Timer Trip Threshold
LX On-Resistance
LX Leakage Current
LX Current Limit
Current-Sense Transresistance
Soft-Start Period
0 < I
LOAD
< 200mA, transient only
V
IN
= 1.8V to 5.5V, FB to COMP
V
FB
= 1.25V
I = 5μA at COMP
FB to COMP
Falling edge
I
LX
= 1.2A
V
LX
= 18V
Duty cycle = 65%
1.6
0.25
0.96
-0.15
50
70
LX not switching, no load on VL
LX switching, no load on VL
990
88
1.216
1.5
3
1170
92
1.235
-1
-0.08
125
160
2400
1
150
0.01
1.9
0.42
3
1.04
300
20
2.2
0.55
+0.15
200
280
2
4
1350
96
1.254
mA
kHz
%
V
%
%/V
nA
μS
V/V
V
m
μA
A
V/A
ms
V
DD
= 3V
V
DD
rising; typical hysteresis 100mV
(Note 1)
V
IN
= 3V, V
FB
= 1.5V, not switching
IN rising; typical hysteresis 100mV
Rising edge, hysteresis = 15 C
I
VL
= 100μA
VL rising, typical hysteresis 200mV
V
FB
= 1.1V
3.15
2.4
10
o
CONDITIONS
MIN
1.8
TYP
4
1.3
MAX
4.0
10
1.75
6.0
0.1
1.75
UNITS
V
μA
V
V
mA
V
o
1.8
0.04
1.4
160
3.3
2.7
C
BOOTSTRAP LINEAR REGULATOR (VL)
3.45
3.0
V
V
mA
2
_______________________________________________________________________________________
Internal-Switch Boost Regulator with
Integrated 3-Channel Scan Driver for TFT LCDs
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= V
DD
= V
SHDN
= +3V, circuit of Figure 2, V
BOOST
= 8V, V
GON
= 23V, V
GOFF
= -12V, V
POS
= 0, V
NEG
= 1.5V, V
OE
= V
CPV
=
V
STV
= V
OECON
= 0,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
OPERATIONAL AMPLIFIER
BOOST Supply Range
BOOST Overvoltage
Fault Threshold
BOOST Undervoltage
Fault Threshold
Large-Signal Voltage Gain
Common-Mode Rejection Ratio
Input Offset Voltage
Input Bias Current
Input Common-Mode
Voltage Range
VCOM Output Voltage
Swing High
VCOM Output Voltage Swing Low
VCOM Output-Current High
VCOM Output-Current Low
Slew Rate
-3dB Bandwidth
VCOM Short-Circuit Current
(Note 2)
(Note 3)
1V < (V
NEG
, V
POS
) < (V
BOOST
- 1V)
1V < (V
NEG
, V
POS
) < (V
BOOST
- 1V)
1V < (V
NEG
, V
POS
) < (V
BOOST
- 1V)
V
BOOST
/2
1V < (V
NEG
, V
POS
) < (V
BOOST
- 1V)
1V < (V
NEG
, V
POS
) < (V
BOOST
- 1V)
I
VCOM
= 5mA
I
VCOM
= -5mA
V
VCOM
= V
BOOST
- 1V
V
VCOM
= 1V
1V < (V
NEG
, V
POS
) < (V
BOOST
- 1V)
1V < (V
NEG
, V
POS
) < (V
BOOST
- 1V)
Short to V
BOOST
/2, sourcing
Short to V
BOOST
/2, sinking
50
50
16.1
Rising edge, 60mV hysteresis
7
Monotonic overtemperature
-2
-1
-3
To GND, V
BOOST
= 18V
To GND, V
BOOST
= 6V
DAC full scale
When OUT is off
To ±0.5 LSB error band
V
SET
+
0.5V
(Note 5)
1000
8.5
2.5
0.05
1
20
18
+1
+2
+2
+3
120
170.0
50.0
15.6
-25
-15
-50
0
V
BOOST
V
BOOST
- 100
- 50
50
-75
+75
40
20
150
150
45.0
16.0
100
5
18.1
19
1.0
120
75
-5
-2.5
+25
+12
+50
V
BOOST
18
19.9
1.4
V
V
V
dB
dB
mV
nA
V
mV
mV
mA
mA
V/μs
MHz
mA
CONDITIONS
MIN
TYP
MAX
UNITS
MAX8798
PROGRAMMABLE VCOM CALIBRATOR
GON Input Range
GON Threshold to Enable Program
SET Voltage Resolution
SET Differential Nonlinearity
SET Zero-Scale Error
SET Full-Scale Error
SET Current
SET External Resistance
(Note 4)
V
SET
/V
BOOST
Voltage Ratio
OUT Leakage Current
OUT Settling Time
OUT Voltage Range
EEPROM Write Cycles
V
V
Bits
LSB
LSB
LSB
μA
k
V/V
nA
μs
V
—
_______________________________________________________________________________________
3
Internal-Switch Boost Regulator with
Integrated 3-Channel Scan Driver for TFT LCDs
MAX8798
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= V
DD
= V
SHDN
= +3V, circuit of Figure 2, V
BOOST
= 8V, V
GON
= 23V, V
GOFF
= -12V, V
POS
= 0, V
NEG
= 1.5V, V
OE
= V
CPV
=
V
STV
= V
OECON
= 0,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
2-WIRE INTERFACE
Logic-Input Low Voltage (V
IL
)
Logic-Input High Voltage (V
IH
)
WPP Logic-Output Low Voltage
WPP Logic-Output High Voltage
SDA, SCL, WPN, V
DD
= 3V
SDA, SCL, WPN, V
DD
= 3V
I
WPP
= 1mA
I
WPP
= 1mA
V
DD
-
0.1
6
-1
5
DC
600
1300
C
BUS
= total capacitance of bus line in pF
C
BUS
= total capacitance of bus line in pF
10% of SDA to 90% of SCL
20 + 10
x C
BUS
20 + 10
x C
BUS
600
600
0
150
600
1300
SDA, SCL (Note 5)
WPN = GND
WPN = VDD
12
-25
V
GON
- V
GOFF
STV, CPV, OE, OECON = AGND
STV, CPV, OE, OECON = AGND
CKV, CKVB, STVP,
-5mA output current
CKV, CKVB, STVP,
5mA output current
V
GOFF
+ 0.2
250
100
V
GOFF
+ 0.05
V
GON
- 0.05
250
V
GON
- 0.2
450
1
20
50
45
-2
65
350
200
V
V
V
μA
μA
V
V
ns
250
300
300
500
+1
0.7 x
V
DD
+0.1
0.3 x
V
DD
V
V
V
V
mA
μA
pF
kHz
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
M
CONDITIONS
MIN
TYP
MAX
UNITS
SDA Logic-Output Low Sink Current SDA forced to 3.3V
Logic Input Current
Input Capacitance
SCL Frequency (f
CLK
)
SCL High Time (t
CLH
)
SCL Low Time (t
CLL
)
SDA, SCL, SCLS Rise Time (t
R
)
SDA, SCL, SCLS Fall Time (t
F
)
START Condition Hold Time
(t
HDSTT
)
START Condition Setup Time
(t
SVSTT
)
Data Input Hold Time (t
HDDAT
)
Data Input Setup Time (t
SUDAT
)
STOP Condition Setup Time
(t
SVSTP
)
Bus Free Time (t
UF
)
Input Filter Spike Suppression (t
SP
)
SCL-SCLS Switch Resistance
HIGH-VOLTAGE SCAN DRIVER
GON Input Voltage Range
GOFF Input Voltage Range
GON to GOFF
GON Supply Current
GOFF Supply Current
Output-Voltage Low
Output-Voltage High
SDA, SCL, SCL_S,WPN to VDD or GND
SDA, SCL, SCL_S
Propagation Delay Between OE
V
CPV
= 0, V
STV
= 0, C
LOAD
= 4.7nF, 50
Rising Edge and CKV/CKVB Edge
4
_______________________________________________________________________________________
Internal-Switch Boost Regulator with
Integrated 3-Channel Scan Driver for TFT LCDs
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= V
DD
= V
SHDN
= +3V, circuit of Figure 2, V
BOOST
= 8V, V
GON
= 23V, V
GOFF
= -12V, V
POS
= 0, V
NEG
= 1.5V, V
OE
= V
CPV
=
V
STV
= V
OECON
= 0,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
Output Slew Rate CKV, CKVB
Propagation Delay Between
STV and STVP
STVP Output Slew Rate
Charge-Sharing Discharge
Path Resistance
DISH Turn-On Threshold
STV, CPV, OE Input Low Voltage
STV, CPV, OE Input High Voltage
OECON Input Low Voltage
OECON Input High Voltage
OECON Sink Current
STV, CPV, OE
Input Current
V
OECON
= 5V = V
DD
V
STV
= V
DD
or GND,
V
CPV
= V
DD
or GND,
V
OE
= V
DD
or GND,
V
OECON
= V
DD
or GND
V
CKV
= GON or GOFF, high impedance
V
CKVB
= GON or GOFF, high impedance
V
CKVCS
= GON or GOFF, high impedance
V
CKVBCS
= GON or GOFF, high impedance
V
STVP
= GON or GOFF, high impedance
SHDN
SHDN,
1.8V < V
IN
< 3.0V
SHDN,
3.0V < V
IN
< 5.5V
V
SHDN
= 0 or 3V
1.8
2.0
-1
+1
2.0
0.4
0.8
1.6
1.5
CONDITIONS
Without charge sharing,
STV = V
DD
, C
LOAD
= 4.7nF, 50
C
LOAD
= 4.7nF
C
LOAD
= 4.7nF, 50
CKV to CKVCS and
CKVB to CKVBCS
Dish falling
20
MIN
20
TYP
40
250
40
250
400
-1.8
0.8
V
V
V
V
V
mA
450
MAX
UNITS
V/μs
ns
V/μs
MAX8798
-1
+1
μA
CKV, CKVB, STVP Output
High-Impedance Current
-1
+1
μA
CONTROL INPUTS
Input Low Voltage
Input High Voltage
SHDN
Input Current
0.6
V
V
μA
ELECTRICAL CHARACTERISTICS
(V
IN
= V
DD
= V
SHDN
= +3V, circuit of Figure 2, V
BOOST
= 8V, V
GON
= 23V, V
GOFF
= -12V, V
POS
= 0, V
NEG
= 1.5V, V
OE
= V
CPV
=
V
STV
= V
OECON
= 0,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 6)
PARAMETER
V
DD
Input Voltage Range
V
DD
Quiescent Current
V
DD
Undervoltage Lockout
IN Input Voltage Range
IN Quiescent Current
IN Undervoltage Lockout
V
DD
= 3V
V
DD
rising; typical hysteresis 100mV
(Note 1)
V
IN
= 3V, V
FB
= 1.5V, not switching
V
IN
rising; typical hysteresis 100mV
1.8
CONDITIONS
MIN
1.8
TYP
MAX
4.0
10
1.75
6.0
0.1
1.75
UNITS
V
μA
V
V
mA
V
_______________________________________________________________________________________
5
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