Download MAX1886 High-Current VCOM Drive Buffer General Description Features

19-2095; Rev 0; 8/01
High-Current VCOM Drive Buffer
Features
♦ Stable with 0.47µF to Unlimited Amount of Output
Capacitance
♦ Over 500mA Peak Drive Current
♦ Excellent Settling Characteristics with Capacitive
Load
♦ +4.5V to +13V Input Supply
♦ 0.45mA Quiescent Current
♦ Thermal Fault Protection
♦ Thin SOT23-5 Package (1.1mm max)
Ordering Information
Applications
Notebook LCD Panels
Monitor LCD Panels
PART
TEMP. RANGE
PIN-PACKAGE
TOP
MARK
MAX1886EZK
-40°C to +85°C
5 Thin SOT23-5*
ADQL
*Requires a special solder temperature profile described in the
Absolute Maximum Ratings section.
Pin Configuration
Typical Operating Circuit
TOP VIEW
VCC
OUT
1
5
FB-
4
FB+
VREF
FB+
OUT
FB-
GND
MAX1886
VO
GND 2
MAX1886
VCC 3
THIN SOT23-5
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1
MAX1886
General Description
The MAX1886 is a high-current operational transconductance 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.
MAX1886
High-Current VCOM Drive Buffer
ABSOLUTE MAXIMUM RATINGS
VCC to GND ............................................................-0.3V to +14V
FB-, FB+, OUT to GND...............................-0.3V to (VCC + 0.3V)
Continuous Power Dissipation (TA = +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
(VCC = 10V, FB- = OUT, VFB+ = 5V, COUT = 0.47µF, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.)
(Note 1)
PARAMETER
SYMBOL
VCC Input Supply Range
VCC
VCC Supply Current
ICC
Input Offset Voltage
VOS
Input Bias Current
IBIAS
CONDITIONS
MIN
450
VFB+ = +5V, no load
µA
mV
5
nA
-100
100
nA
|VOS| < 10mV over CMR
1.2
VCC 1.2V
V
+1.2V < VCM < +8.8V
VCM
Power-Supply Rejection Ratio
PSRR
+4.5V < VCC < +13V, VFB+ = +2.25V
70
Common-Mode Rejection Ratio
CMRR
+1.2V < VCM < +8.8V
70
Gain-Bandwidth Product
GBW
Small signal
dB
1/6πCL
Small signal (±1mV overdrive)
0.3
Large signal (±30mV overdrive)
10
±100mV overdrive,
VOUT = 3V or 7V
IOUT
V
900
100
Common-Mode Input Range
Output Current Drive
UNITS
13
-5
IOS
gm
MAX
-100
Input Offset Current
Transconductance
TYP
4.5
TA = -40°C to +85°C
±175
TA = 0°C to +85°C
±250
±550
S
mA
Thermal Shutdown
170
°C
Thermal Shutdown Hysteresis
15
°C
Note 1: The MAX1886 is 100% production tested at TA = +25°C. Specifications over temperature are guaranteed by design.
SUPPLY
VOLTAGE
REFERENCE
VOLTAGE
3
4
0.47
2
0.47
5
VX
1
MAX1886
RL
CL
Figure 1. Load Transient Test Circuit
2
Hz
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High-Current VCOM Drive Buffer
INPUT OFFSET VOLTAGE DEVIATION
vs. TEMPERATURE
0.2
0.02
0.1
0
0
∆VOS (mV)
-0.02
-0.04
-0.1
-0.2
-0.06
-0.08
-0.3
-0.10
-0.4
6
7
8
9
10 11 12 13 14
2
TA = +85°C
0
-40
-15
10
35
60
-40
85
-30
-20
-10
0
10
20
TEMPERATURE (°C)
OUTPUT CURRENT (mA)
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
NO-LOAD SUPPLY CURRENT
vs. TEMPERATURE
LOAD TRANSIENT ±10V
0.9
0.8
SUPPLY CURRENT (mA)
+25°C
0.4
0.3
1.0
MAX1886 toc04
+85°C
-40°C
0.2
0.6
0.4
8.5
10.5
IOUT
500mA/div
0.3
VX
10V/div
RL = 2.5Ω, CL = 100nF, FIGURE 1
0
6.5
40
VOUT
200mV/div
AC-COUPLED
0.5
0.1
0
30
0.7
0.2
0.1
4.5
TA = +25°C
3
VCC (V)
0.6
0.5
TA = -40°C
4
MAX1886 toc06
5
5
1
MAX1886 toc05
4
6
-40
12.5
-15
10
35
60
85
4µs/div
TEMPERATURE (°C)
SUPPLY VOLTAGE (V)
SHORT-CIRCUIT WAVEFORMS
MAX1886 toc07
VOS (mV)
0.04
SUPPLY CURRENT (mA)
VCC = 10V
VCM = VCC/2
0.3
MAX1886 toc03
0.06
0.4
TRANSCONDUCTANCE (S)
VCM = VCC/2
0.08
MAX1886 toc01
0.10
TRANSCONDUCTANCE
vs. OUTPUT CURRENT
MAX1886 toc02
INPUT OFFSET VOLTAGE DEVIATION
vs. SUPPLY VOLTAGE
ICC
500mA/div
IOUT
500mA/div
VOUT
5V/div
VCC
5V/div
20ms/div
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3
MAX1886
Typical Operating Characteristics
(VCC = 10V, COUT = 1µF, VCM = 5V, TA = +25°C, unless otherwise noted.)
Typical Operating Characteristics (continued)
(VCC = 10V, COUT = 1µF, VCM = 5V, TA = +25°C, unless otherwise noted.)
SUPPLY CAPACITOR
CHARGING CURRENT
ICC
500mA/div
ICC
500mA/div
VCC
10V/div
VCC
10V/div
VFB+
5V/div
VFB+
5V/div
VOUT
5V/div
COUT = 0.47µF
MAX1886 toc09
STARTUP WAVEFORMS
WITH SOFT-START
STARTUP WAVEFORM
WITHOUT SOFT-START
MAX1886 toc08
MAX1886
High-Current VCOM Drive Buffer
VOUT
5V/div
COUT = 0.47µF
500µs/div
5µs/div
Pin Description
PIN
NAME
DESCRIPTION
1
OUT
Output of Buffer Amplifier. Requires a minimum 0.47µF ceramic filter capacitor to GND. Place the
capacitor close to OUT.
2
GND
Ground
3
VCC
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.
4
FB+
Noninverting Input to Buffer Amplifier
5
FB-
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 driving 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 = gm/COUT
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 bandwidth 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 stability, 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 VCC 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
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High-Current VCOM Drive Buffer
SWITCHING
REGULATOR
MAX1886
VIN
SOURCE DRIVER VOLTAGE
C1
PC BOARD PARASITICS
3
LINEAR
REGULATOR
C2
0.47µF
4
2
OPTIONAL REFERENCE
VOLTAGE CIRCUIT
0.47µF
5
1
GAMMA CORRECTION
REFERENCE VOLTAGE
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 linear regulator will reject the ripple voltage produced by
the source drivers (see Figure 2). The output of this linear regulator can also be used for the gamma correction reference voltage.
Chip Information
TRANSISTOR COUNT: 121
PROCESS: BiCMOS
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High-Current VCOM Drive Buffer
MAX1886
Package Information
6
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High-Current VCOM Drive Buffer
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 _____________________ 7
© 2001 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
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MAX1886
Package Information (continued)