19-2095; Rev 0; 8/01
High-Current VCOM Drive Buffer
General Description
The MAX1886 is a high-current operational transcon-
ductance amplifier. The MAX1886 is ideal for driving
the backplane of an active matrix, dot inversion thin film
transistor (TFT) liquid crystal display (LCD). The
MAX1886’s high >500mA peak-current drive capability
provides fast response to pulsed load conditions. The
MAX1886 is stable from 0.47µF to an unlimited amount
of output capacitance.
The MAX1886 is available in the low-profile (1.1mm
max) 5-pin Thin SOT23 package and fully specified
over the -40°C to +85°C extended temperature range.
Features
o
Stable with 0.47µF to Unlimited Amount of Output
Capacitance
o
Over 500mA Peak Drive Current
o
Excellent Settling Characteristics with Capacitive
Load
o
+4.5V to +13V Input Supply
o
0.45mA Quiescent Current
o
Thermal Fault Protection
o
Thin SOT23-5 Package (1.1mm max)
MAX1886
Applications
Notebook LCD Panels
Monitor LCD Panels
PART
MAX1886EZK
Ordering Information
TEMP. RANGE
-40°C to +85°C
PIN-PACKAGE
5 Thin SOT23-5*
TOP
MARK
ADQL
*Requires
a special solder temperature profile described in the
Absolute Maximum Ratings section.
Typical Operating Circuit
V
CC
Pin Configuration
TOP VIEW
OUT
1
5
FB-
V
REF
FB+
OUT
V
O
GND
2
MAX1886
FB-
GND
MAX1886
V
CC
3
4
FB+
THIN SOT23-5
________________________________________________________________
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.
High-Current VCOM Drive Buffer
MAX1886
ABSOLUTE MAXIMUM RATINGS
V
CC
to GND ............................................................-0.3V to +14V
FB-, FB+, OUT to GND...............................-0.3V to (V
CC
+ 0.3V)
Continuous Power Dissipation (T
A
= +70°C)
5-Pin Thin SOT23 (derate 7.1mW°C above +70°C) .....727mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
This device is constructed using a unique set of packaging techniques that impose a limit on the thermal profile the device can be exposed to during
board level solder attach and rework. Maxim recommends the use of the solder profiles recommended in the industry-standard specification, JEDEC
020A, paragraph 7.6, Table 3 for IR/VPR and convection reflow processes. Preheating, per this standard, is required. Hand or wave soldering is not
recommended.
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
= 10V, FB- = OUT, V
FB+
= 5V, C
OUT
= 0.47µF, T
A
= -40°C to +85°C, unless otherwise noted. Typical values are at T
A
= +25°C.)
(Note 1)
PARAMETER
V
CC
Input Supply Range
V
CC
Supply Current
Input Offset Voltage
Input Bias Current
Input Offset Current
Common-Mode Input Range
Power-Supply Rejection Ratio
Common-Mode Rejection Ratio
Gain-Bandwidth Product
Transconductance
Output Current Drive
Thermal Shutdown
Thermal Shutdown Hysteresis
SYMBOL
V
CC
I
CC
V
OS
I
BIAS
I
OS
V
CM
PSRR
CMRR
GBW
g
m
I
OUT
V
FB+
= +5V, no load
+1.2V < V
CM
< +8.8V
-5
-100
-100
1.2
70
70
1/6πC
L
0.3
10
±175
±250
170
15
±550
CONDITIONS
MIN
4.5
450
TYP
MAX
13
900
5
100
100
V
CC
-
1.2V
UNITS
V
µA
mV
nA
nA
V
dB
Hz
S
mA
°C
°C
|
V
OS
|
< 10mV over CMR
+4.5V < V
CC
< +13V, V
FB+
= +2.25V
+1.2V < V
CM
< +8.8V
Small signal
Small signal (±1mV overdrive)
Large signal (±30mV overdrive)
±100mV overdrive,
V
OUT
= 3V or 7V
T
A
= -40°C to +85°C
T
A
= 0°C to +85°C
Note 1:
The MAX1886 is 100% production tested at T
A
= +25°C. Specifications over temperature are guaranteed by design.
SUPPLY
VOLTAGE
REFERENCE
VOLTAGE
3
4
2
5
1
0.47
V
X
R
L
C
L
0.47
MAX1886
Figure 1. Load Transient Test Circuit
2
_______________________________________________________________________________________
High-Current VCOM Drive Buffer
Typical Operating Characteristics
(V
CC
= 10V, C
OUT
= 1µF, V
CM
= 5V, T
A
= +25°C, unless otherwise noted.)
INPUT OFFSET VOLTAGE DEVIATION
vs. SUPPLY VOLTAGE
MAX1886 toc01
MAX1886
INPUT OFFSET VOLTAGE DEVIATION
vs. TEMPERATURE
MAX1886 toc02
TRANSCONDUCTANCE
vs. OUTPUT CURRENT
MAX1886 toc03
0.10
0.08
0.06
0.04
V
OS
(mV)
0.02
V
CM
= V
CC
/2
0.4
0.3
0.2
0.1
∆V
OS
(mV)
0
-0.1
-0.2
-0.3
-0.4
V
CC
= 10V
V
CM
= V
CC
/2
6
5
TRANSCONDUCTANCE (S)
T
A
=
-40°C
4
T
A
=
+25°C
3
2
1
T
A
=
+85°C
0
0
-0.02
-0.04
-0.06
-0.08
-0.10
4
5
6
7
8
9
V
CC
(V)
10 11 12 13 14
-40
-15
10
35
60
85
-40
-30
-20
-10
0
10
20
30
40
TEMPERATURE (°C)
OUTPUT CURRENT (mA)
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX1886 toc04
NO-LOAD SUPPLY CURRENT
vs. TEMPERATURE
MAX1886 toc05
LOAD TRANSIENT
±10V
I
OUT
500mA/div
MAX1886 toc06
0.6
0.5
SUPPLY CURRENT (mA)
0.4
0.3
0.2
0.1
0
4.5
6.5
8.5
10.5
12.5
SUPPLY VOLTAGE (V)
-40°C
+85°C
+25°C
1.0
0.9
0.8
SUPPLY CURRENT (mA)
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
-40
-15
10
35
60
V
OUT
200mV/div
AC-COUPLED
V
X
10V/div
R
L
= 2.5Ω, C
L
= 100nF, FIGURE 1
85
4µs/div
TEMPERATURE (°C)
SHORT-CIRCUIT WAVEFORMS
I
CC
500mA/div
MAX1886 toc07
I
OUT
500mA/div
V
OUT
5V/div
V
CC
5V/div
20ms/div
_______________________________________________________________________________________
3
High-Current VCOM Drive Buffer
MAX1886
Typical Operating Characteristics (continued)
(V
CC
= 10V, C
OUT
= 1µF, V
CM
= 5V, T
A
= +25°C, unless otherwise noted.)
STARTUP WAVEFORMS
WITH SOFT-START
MAX1886 toc08
MAX1886 toc09
STARTUP WAVEFORM
WITHOUT SOFT-START
I
CC
500mA/div
SUPPLY CAPACITOR
CHARGING CURRENT
I
CC
500mA/div
V
CC
10V/div
V
FB+
5V/div
V
OUT
5V/div
500µs/div
V
CC
10V/div
V
FB+
5V/div
V
OUT
5V/div
5µs/div
C
OUT
= 0.47µF
C
OUT
= 0.47µF
Pin Description
PIN
1
2
3
4
5
NAME
OUT
GND
V
CC
FB+
FB-
DESCRIPTION
Output of Buffer Amplifier. Requires a minimum 0.47µF ceramic filter capacitor to GND. Place the
capacitor close to OUT.
Ground
Voltage-Supply Input. Bypass to GND with a 0.47µF capacitor close to the pin. Use the output
capacitor of the preceding voltage regulator as the additional filter capacitor.
Noninverting Input to Buffer Amplifier
Inverting Input to Buffer Amplifier. Feedback must be taken from the output filter capacitor terminal.
Detailed Description
The MAX1886 operational transconductance amplifier
(OTA) provides high-current output that is ideal for dri-
ving capacitive loads such as the backplane of a TFT
LCD panel. The positive feedback input, FB+, allows
common-mode biasing to mid-supply, or other VCOM
voltage.
The MAX1886 unity-gain bandwidth is GBW = g
m
/C
OUT
where g
m
is the amplifier’s transconductance.
Transconductance is the ratio of the output current to
the input voltage. The gain of the amplifier is dependent
upon the load. The MAX1886 requires only a small
0.47µF ceramic output capacitor for stability. The band-
width is inversely proportional to the output capacitor,
so large capacitive loads improve stability; however,
lower bandwidth decreases the buffer’s transient
response time. To improve the transient response
4
times, the MAX1886’s transconductance increases as
the output current increases (see
Typical Operating
Characteristics).
Applications Information
Output Filter Capacitor
The MAX1886 requires a minimum of 0.47µF output
capacitance placed close to OUT. To ensure buffer sta-
bility, the output capacitor ESR must be 50mΩ or lower.
Ceramic capacitors are an excellent choice.
Input Bypass Capacitor
The MAX1886 requires a 0.47µF input bypass capacitor
(C2) close to the V
CC
supply input (see Figure 2). Place
the MAX1886 close to the preceding voltage regulator
output capacitor so that the MAX1886 shares the same
capacitor (C1). Minimize trace length and use wide
_______________________________________________________________________________________
High-Current VCOM Drive Buffer
MAX1886
V
IN
SWITCHING
REGULATOR
C1
SOURCE DRIVER VOLTAGE
PC BOARD PARASITICS
LINEAR
REGULATOR
3
4
2
C2
0.47µF
OPTIONAL REFERENCE
VOLTAGE CIRCUIT
GAMMA CORRECTION
REFERENCE VOLTAGE
5
1
0.47µF
TO LCD
BACKPLANE
MAX1886
Figure 2. Typical TFT LCD Backplane Drive Circuit
traces between the voltage regulator output and the
MAX1886 V
CC
input to reduce PC board parasitics
(inductance, resistance, and capacitance), which can
cause undesired ringing.
Voltage Reference
The reference voltage for the MAX1886 input can be
produced using the output of a linear regulator. The lin-
ear regulator will reject the ripple voltage produced by
the source drivers (see Figure 2). The output of this lin-
ear regulator can also be used for the gamma correc-
tion reference voltage.
Chip Information
TRANSISTOR COUNT: 121
PROCESS: BiCMOS
_______________________________________________________________________________________
5
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