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19-2095; Rev 0; 8/01
High-Current VCOM Drive Buffer
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 0.47F 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 -40C to +85C extended temperature range.
Features
o Stable with 0.47F 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 -40C to +85C 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
VCC
Pin Configuration
TOP VIEW
OUT 1 5 FB-
VREF FB+ OUT VO GND 2
MAX1886
FB-
GND
MAX1886
VCC 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
VCC to GND ............................................................-0.3V to +14V FB-, FB+, OUT to GND...............................-0.3V to (VCC + 0.3V) Continuous Power Dissipation (TA = +70C) 5-Pin Thin SOT23 (derate 7.1mWC above +70C) .....727mW Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C
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 = 0.47F, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER VCC Input Supply Range VCC 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 VCC ICC VOS IBIAS IOS VCM PSRR CMRR GBW gm IOUT VFB+ = +5V, no load +1.2V < VCM < +8.8V -5 -100 -100 1.2 70 70 1/6CL 0.3 10 175 250 170 15 550 CONDITIONS MIN 4.5 450 TYP MAX 13 900 5 100 100 VCC 1.2V UNITS V A mV nA nA V dB Hz S mA C C
|VOS| < 10mV over CMR
+4.5V < VCC < +13V, VFB+ = +2.25V +1.2V < VCM < +8.8V Small signal Small signal (1mV overdrive) Large signal (30mV overdrive) 100mV overdrive, VOUT = 3V or 7V TA = -40C to +85C TA = 0C to +85C
Note 1: The MAX1886 is 100% production tested at TA = +25C. Specifications over temperature are guaranteed by design.
SUPPLY VOLTAGE
REFERENCE VOLTAGE
3 4 2 5 1 0.47 VX RL CL 0.47
MAX1886
Figure 1. Load Transient Test Circuit 2 _______________________________________________________________________________________
High-Current VCOM Drive Buffer
Typical Operating Characteristics
(VCC = 10V, COUT = 1F, VCM = 5V, TA = +25C, 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 VOS (mV) 0.02 VCM = VCC/2
0.4 0.3 0.2 0.1 VOS (mV) 0 -0.1 -0.2 -0.3 -0.4 VCC = 10V VCM = VCC/2
6 5 TRANSCONDUCTANCE (S) TA = -40C 4 TA = +25C 3 2 1 TA = +85C 0
0 -0.02 -0.04 -0.06 -0.08 -0.10 4 5 6 7 8 9 VCC (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
IOUT 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) -40C +85C +25C
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
VOUT 200mV/div AC-COUPLED
VX 10V/div RL = 2.5, CL = 100nF, FIGURE 1 85 4s/div TEMPERATURE (C)
SHORT-CIRCUIT WAVEFORMS
ICC 500mA/div
MAX1886 toc07
IOUT 500mA/div
VOUT 5V/div VCC 5V/div 20ms/div
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High-Current VCOM Drive Buffer MAX1886
Typical Operating Characteristics (continued)
(VCC = 10V, COUT = 1F, VCM = 5V, TA = +25C, unless otherwise noted.)
STARTUP WAVEFORMS WITH SOFT-START
MAX1886 toc08 MAX1886 toc09
STARTUP WAVEFORM WITHOUT SOFT-START
ICC 500mA/div SUPPLY CAPACITOR CHARGING CURRENT
ICC 500mA/div VCC 10V/div VFB+ 5V/div VOUT 5V/div 500s/div
VCC 10V/div VFB+ 5V/div VOUT 5V/div 5s/div
COUT = 0.47F
COUT = 0.47F
Pin Description
PIN 1 2 3 4 5 NAME OUT GND VCC FB+ FBDESCRIPTION Output of Buffer Amplifier. Requires a minimum 0.47F ceramic filter capacitor to GND. Place the capacitor close to OUT. Ground Voltage-Supply Input. Bypass to GND with a 0.47F 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 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 0.47F 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 0.47F output capacitance placed close to OUT. To ensure buffer stability, the output capacitor ESR must be 50m or lower. Ceramic capacitors are an excellent choice.
Input Bypass Capacitor
The MAX1886 requires a 0.47F 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 MAX1886
VIN
SWITCHING REGULATOR C1
SOURCE DRIVER VOLTAGE PC BOARD PARASITICS
LINEAR REGULATOR
3 4 2 C2 0.47F
OPTIONAL REFERENCE VOLTAGE CIRCUIT GAMMA CORRECTION REFERENCE VOLTAGE
5 1
0.47F 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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5
High-Current VCOM Drive Buffer MAX1886
Package Information
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High-Current VCOM Drive Buffer
Package Information (continued)
MAX1886
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 (c) 2001 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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