19-0737; Rev 0; 1/07
KIT
ATION
EVALU
BLE
AVAILA
Step-Up Regulator, Internal Charge Pumps, Switch
Control, and Operational Amplifier for TFT LCDs
General Description
The MAX8784 generates supply rails for the thin-film
transistor (TFT) liquid-crystal display (LCD) panels in TVs
and monitors. It includes a step-up regulator, a regulated
positive and a negative charge-pump, three high-current
operational amplifiers, and Dual Mode™, logic-con-
trolled, high-voltage switch control block. HVS mode
automatically increases the output voltages of the boost
regulator and the positive charge-pump to stress test
display panels during production. The MAX8784 can
operate from input voltages of 4V to 5.5V and is opti-
mized for LCD TV panel and LCD monitor applications.
The step-up DC-DC regulator provides a regulated sup-
ply voltage for TFT source drivers. The step-up regulator
is a high-frequency (1.2MHz), high-efficiency, current-
mode regulator. The step-up regulator has a built-in
110mΩ (typ) power MOSFET. The high-switching fre-
quency allows the use of ultra-small inductors and
ceramic capacitors. The current-mode architecture pro-
vides fast transient response and easy compensation.
The step-up regulator features output undervoltage pro-
tection, soft-start, internal current limit, and adjustable
output voltage by an external resistive divider.
The three operational amplifiers drive the LCD back-
plane and the gamma-correction-divider string. Each
operational amplifier has a fast slew rate (45V/µs), a
wide bandwidth (20MHz), and a high-output short-cir-
cuit current (200mA). Each op amp has rail-to-rail input
and rail-to-rail output operation.
The positive charge-pump regulator and the negative
charge-pump regulator provide regulated supply volt-
ages for the TFT gate drivers. The positive charge
pump is a two-stage charge pump, which requires no
external diodes. The output voltages of both charge
pumps are resistor adjustable. The logic-controlled
high-voltage switch allows the manipulation of the posi-
tive TFT gate-driver supply.
The MAX8784 is available in a small (5mm x 5mm), low-
profile (0.8mm), 40-pin TQFN package and operates
over the -40°C to +85°C temperature range.
Features
o
Step-Up Regulator Supply for LCD Panel Source
Driver
Fast Transient Response to Pulsed Load
Built-In 18V, 4A, 0.11Ω n-Channel Power
MOSFET with Lossless Current Sensing
Cycle-by-Cycle Current-Limit Comparator
90% Efficiency (5V In to 15V Out)
1.2MHz Switching Frequency
o
Three High-Current 19V Operational Amplifiers
180mA Output Short-Circuit Current
45V/µs Slew Rate
20MHz Bandwidth
Rail-to-Rail Input and Output Operation
o
Regulated Charge-Pump Tripler with Integrated
Diodes for TFT Gate-On Supply
o
Regulated Charge Pump for TFT Gate-Off Supply
o
Built-In Sequencing
Internal Digital Soft-Start
36V Gate-On Switch
Startup Timing Capacitors for AVDD and GON
o
Undervoltage and Thermal Protection
o
4V to 5.5V Input Operating Range
MAX8784
Simplified Operating Circuit
VIN
STEP-UP
OUTPUT
V
CC
POS1
TO
VCOM
STEP-UP
OUTPUT
NEG1
OUT1
POS2
NEG2
OUT2
POS3
OUT3
HVS
REF
AGND
FBN
LX
PGND
FB
COMP
TO
VCOM
TO
VCOM
RSET
GDEL
ADEL
VIN
MAX8784
CTL
SHDN
GON
DRN
TCON
ON/OFF
VGON
Applications
LCD TVs and LCD Monitors
Ordering Information
PART
MAX8784ETL+
TEMP RANGE
-40°C to +85°C
PIN-
PACKAGE
40 TQFN
5mm x 5mm
PKG CODE
T4055-1
VGOFF
DRVN
PGND
POUT
FBP
SUP C1N
C1P C2N
C2P
STEP-UP
OUTPUT
+Denotes
a lead(Pb)-free/RoHS-compliant package.
STEP-UP
OUTPUT
Dual Mode is a trademark of Maxim Integrated Products, Inc.
________________________________________________________________
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.
Step-Up Regulator, Internal Charge Pumps, Switch
Control, and Operational Amplifier for TFT LCDs
MAX8784
ABSOLUTE MAXIMUM RATINGS
V
CC
, CTL, HVS,
SHDN,
ADEL, GDEL to AGND ....-0.3V to +7.5V
REF, COMP, FB, FBN, FBP to AGND .........-0.3V to (V
CC
+ 0.3V)
POS1, NEG1, POS2, NEG2, POS3, OUT1, OUT2,
OUT3 to AGND .......................................-0.3V to (V
SUP
+ 0.3)
PGND, BGND to AGND.........................................-0.3V to +0.3V
LX, RSET to PGND .................................................-0.3V to +22V
SUP to AGND .........................................................-0.3V to +22V
DRVN to AGND.........................................-0.3V to (V
SUP
+ 0.3V)
C1N, C2N to AGND ..................................-0.3V to (V
SUP
+ 0.3V)
C1P to AGND .........................................................-0.3V to +30V
POUT to C2P, C1P to C2P......................................-0.3V to +22V
C2P, POUT to AGND..............................................-0.3V to +40V
GON, DRN to AGND ..............................................-0.3V to +40V
DRN to GON............................................................-30V to +30V
REF Short Circuit to AGND.........................................Continuous
RMS V
CC
Current ................................................................50mA
RMS DRVN Current...........................................................400mA
LX, PGND RMS Current Rating.............................................2.4A
Continuous Power Dissipation (T
A
= +70°C)
40-Pin TQFN (derate 35.7mW/°C above +70°C) .......2857mW
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
Soldering Temperature (reflow) .......................................+260°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
CC
= +5V, Circuit of Figure 1, AVDD = SUP = +14V,
T
A
= 0°C to +85°C.
Typical values are at T
A
= +25°C, unless otherwise noted.)
PARAMETER
V
CC
Input Supply Range
V
CC
Undervoltage Lockout Threshold
V
CC
rising, typical hysteresis = 50mV
V
FB
= 1.3V, not switching
V
CC
Quiescent Current
V
FB
= 1.1V, switching, no load, V
SUP
disconnected,
V
FBP
= V
CC
, V
FBN
= 0V
SHDN
= GND
SHDN
Input Low Voltage
SHDN
Input High Voltage
SHDN
Input Current
REFERENCE
REF Output Voltage
REF Load Regulation
REF Sink Current
REF Undervoltage Lockout Threshold
OSCILLATOR AND TIMING
Frequency
Oscillator Maximum Duty Cycle
Duration to Trigger Fault Condition
ADEL, GDEL Capacitor Charge Current
ADEL, GDEL Turn-On Threshold
STEP-UP REGULATOR
FB Regulation Voltage
FB Fault-Trip Level
FB Load Regulation
FB Line Regulation
FB Input Bias Current
FB = COMP, C
COMP
= 1nF
FB = COMP, C
COMP
= 1nF, +25°C to +85°C
Falling edge
0 < I
LOAD
< full
V
CC
= 4.5V to 5.5V
V
FB
= 1.25V
1.235
1.238
0.96
1.246
1.246
1.00
-1
0.25
100
200
1.256
1.256
1.04
V
V
%
%/V
nA
1000
87
47
4
1200
90
55
5
1.25
1400
93
65
6
1.32
kHz
%
ms
µA
V
No external load
0 < I
LOAD
< 50µA
In regulation
Rising edge, typical hysteresis = 200mV
10
1.0
1.15
1.238
1.250
1.262
10
V
mV
µA
V
1.8
-1
+1
CONDITIONS
MIN
4.0
2.4
2.6
1.0
4
6
0.05
0.8
V
V
µA
mA
TYP
MAX
5.5
2.8
UNITS
V
V
2
_______________________________________________________________________________________
Step-Up Regulator, Internal Charge Pumps, Switch
Control, and Operational Amplifier for TFT LCDs
ELECTRICAL CHARACTERISTICS (continued)
(V
CC
= +5V, Circuit of Figure 1, AVDD = SUP = +14V,
T
A
= 0°C to +85°C.
Typical values are at T
A
= +25°C, unless otherwise noted.)
PARAMETER
FB Transconductance
LX Current Limit
LX On-Resistance
Current-Sense Transresistance
Soft-Start Period
V
SUP
Input Supply Range
V
SUP
Overvoltage Charge-Pump Inhibit
FBP Regulation Voltage
FBP Line Regulation Error
FBP Input Bias Current
POUT Output-Voltage Range
POUT Fixed Output Voltage
POUT Output Current Limit
C1N, C2N High-Side On-Resistance
C1N, C2N Low-Side On-Resistance
C1P Switch On-Resistance
C2P Switch On-Resistance
POUT Switch On-Resistance
FBP Fault-Trip Level
Falling edge
0.96
1.00
3
0.985
-50
0.1
10
6
Rising edge
450
3
0.8
1.8
CTL = 0V or V
CC
-1
200
200
V
GDEL
= 1.5V, CTL = V
CC
V
POUT
- V
GON
> 5V
V
GDEL
= 1.5V, CTL = 0V
V
GON
- V
DRN
> 5V
V
GDEL
= 1.0V
35
100
180
60
10
20
+1
1.00
1.015
+50
Positive Charge-Pump Soft-Start Period 7-bit voltage ramp
NEGATIVE CHARGE-PUMP REGULATOR
FBN Regulation Voltage
FBN Input Bias Current
FBN Line Regulation Error
DRVN PCH On-Resistance
DRVN NCH On-Resistance
FBN Fault-Trip Level
Negative Charge-Pump Soft-Start Period 7-bit voltage ramp
POSITIVE GATE-DRIVER TIMING AND CONTROL SWITCHES
CTL Input-Low Voltage
CTL Input-High Voltage
CTL Input Current
CTL-to-GON Rising Propagation Delay
CTL-to-GON Falling Propagation Delay
GON-to-POUT Switch On-Resistance
GON-to-POUT Switch Saturation Current
GON-to-DRN Switch On-Resistance
GON-to-DRN Switch Saturation Current
GON-to-PGND Switch On-Resistance
V
V
µA
ns
ns
Ω
mA
Ω
mA
kΩ
V
REF
- V
FBN
V
FBN
= 250mV
V
SUP
= 11V to 19V, VGOFF = -9V, I
VGOFF
= -20mA
V
nA
%/V
Ω
Ω
mV
ms
V
SUP
= 10V ~ 19V, V
POUT
= 28V
V
FBP
= 1.5V
I
VGON
= 0mA
HVS = V
CC
, I
POUT
= 0mA
Not in dropout, V
SUP
= 9V, V
POUT
= 24V
29.1
20
30
50
9.0
6.0
15.0
10.0
10.0
1.04
-100
V
SUP
= rising, typical hysteresis = 200mV
7-bit current ramp
6
20
1.225
21
1.25
0.1
+100
36
30.9
POSITIVE CHARGE-PUMP REGULATOR
19
22
1.275
V
V
V
%/V
nA
V
V
mA
Ω
Ω
Ω
Ω
Ω
V
ms
CONDITIONS
∆I
COMP
= ±2.5µA, FB = COMP
V
FB
= 1.1V, duty cycle = 75%
I
LX
= 1.0A
0.10
MIN
75
3.5
TYP
160
4.0
0.10
0.20
3
MAX
280
4.6
0.19
0.26
UNITS
µS
A
Ω
V/A
ms
MAX8784
_______________________________________________________________________________________
3
Step-Up Regulator, Internal Charge Pumps, Switch
Control, and Operational Amplifier for TFT LCDs
MAX8784
ELECTRICAL CHARACTERISTICS (continued)
(V
CC
= +5V, Circuit of Figure 1, AVDD = SUP = +14V,
T
A
= 0°C to +85°C.
Typical values are at T
A
= +25°C, unless otherwise noted.)
PARAMETER
OPERATIONAL AMPLIFIERS
SUP Supply Range
SUP Overvoltage Fault Threshold
SUP Supply Current
Input Offset Voltage
Input Bias Current
Input Common-Mode Voltage Range
Input Common-Mode Rejection Ratio
1V < V
NEGx
, V
POSx
< (V
SUP
- 1)
I
OUTx
= 1mA
Output Voltage-Swing High
I
OUTx
= 25mA
Output Voltage-Swing Low
Large-Signal Voltage Gain
Slew Rate
-3dB Bandwidth
Short-Circuit Current
HVS FUNCTION
HVS Input-Low Voltage
HVS Input-High Voltage
HVS Input Pulldown Resistance
RSET Output On-Resistance
RSET Output Leakage
HVS = V
CC
HVS = AGND
1.8
5
10
5
50
20
1
0.8
V
V
kΩ
Ω
µA
I
OUTx
= -1mA
I
OUTx
= -25mA
V
OUTx
= 1V to V
SUP
- 1V
C
LOAD
= 20pF
C
LOAD
= 20pF
Short to V
SUP
/ 2, sourcing
Short to V
SUP
/ 2, sinking
80
45
20
140
220
V
SUP
-
50
V
SUP
-
300
50
300
(Note 1)
Buffer configuration, V
POSx
= V
SUP
/ 2, no load
V
NEGx
, V
POSx
= V
SUP
/ 2,
V
NEGx
, V
POSx
= V
SUP
/ 2
-1
0
80
6
19.1
20
11
19
21.0
15
12
+1
V
SUP
V
V
mA
mV
µA
V
dB
CONDITIONS
MIN
TYP
MAX
UNITS
mV
mV
dB
V/µs
MHz
mA
ELECTRICAL CHARACTERISTICS
(V
CC
= +5V, Circuit of Figure 1, AVDD = SUP = +14V,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 2)
PARAMETER
V
CC
Input Supply Range
V
CC
Undervoltage Lockout Threshold
V
CC
Quiescent Current
SHDN
Input-Low Voltage
SHDN
Input-High Voltage
1.8
V
CC
rising, typical hysteresis = 50mV
V
FB
= 1.1V, switching, no load, AVDD isolated
from SUP, V
FBP
= V
CC
, V
FBN
= 0V
SHDN
= GND
CONDITIONS
MIN
4.0
2.4
TYP
MAX
5.5
2.8
6
0.05
0.8
V
V
UNITS
V
V
mA
4
_______________________________________________________________________________________
Step-Up Regulator, Internal Charge Pumps, Switch
Control, and Operational Amplifier for TFT LCDs
ELECTRICAL CHARACTERISTICS (continued)
(V
CC
= +5V, Circuit of Figure 1, AVDD = SUP = +14V,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 2)
PARAMETER
REFERENCE
REF Output Voltage
REF Load Regulation
REF Sink Current
REF Undervoltage Lockout Threshold
OSCILLATOR AND TIMING
Frequency
Oscillator Maximum Duty Cycle
Duration-to-Trigger Fault Condition
ADEL, GDEL Capacitor Charge Current
ADEL, GDEL Turn-On Threshold
STEP-UP REGULATOR
FB Regulation Voltage
FB Fault Trip Level
FB Transconductance
LX Current Limit
LX On-Resistance
Current-Sense Transresistance
POSITIVE CHARGE-PUMP REGULATOR
V
SUP
Input Supply Range
V
SUP
Overvoltage Charge-Pump Inhibit
FBP Regulation Voltage
POUT Output-Voltage Range
POUT Fixed-Output Voltage
POUT Output-Current Limit
C1N, C2N High-Side On-Resistance
C1N, C2N Low-Side On-Resistance
C1P Switch On-Resistance
CP2 Switch On-Resistance
POUT Switch On-Resistance
FBP Fault Trip Level
FBN Regulation Voltage
DRVN PCH On-Resistance
DRVN NCH On-Resistance
Falling edge
V
REF
- V
FBN
0.96
0.985
NEGATIVE CHARGE-PUMP REGULATOR
1.015
10
6
V
Ω
Ω
I
POUT
= 0mA
HVS = V
CC
, I
POUT
= 0mA
Not in dropout, V
SUP
= 9V V
POUT
= 24V
V
SUP
= rising, typical hysteresis = 200mV
6
20
1.225
V
SUP
29.1
20
9
6
15
10
10
1.04
19
22
1.275
36
30.9
V
V
nA
V
V
mA
Ω
Ω
Ω
Ω
Ω
V
FB = COMP, C
COMP
= 1nF
Falling edge
∆I
COMP
= ±2.5µA, FB = COMP
V
FB
= 1.1V, duty cycle = 75%
I
LX
= 1.0A
0.10
1.230
0.96
75
3.0
1.262
1.04
280
5.0
0.19
0.26
V
V
µS
A
Ω
V/A
950
87
47
4
1.18
1400
93
69
6
1.32
kHz
%
ms
µA
V
No external load
0 < I
LOAD
< 50µA
In regulation
Rising edge, typical hysteresis = 200mV
10
1.15
1.232
1.262
10
V
mV
µA
V
CONDITIONS
MIN
TYP
MAX
UNITS
MAX8784
_______________________________________________________________________________________
5
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