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19-4110; Rev 3; 10/09
KIT ATION EVALU BLE AVAILA
1A, 4-Bump UCSP/SOT23, Precision Current-Sense Amplifier
General Description Features
o Ultra-Low Supply Current of 1A (max) o Low 500V (max) Input Offset Voltage o Low < 0.5% (max) Gain Error o Input Common Mode: +1.6V to +28V o Voltage Output o Three Gain Versions Available 25V/V (MAX9938T) 50V/V (MAX9938F) 100V/V (MAX9938H) 200V/V (MAX9938W) o Tiny 1mm x 1mm x 0.6mm, 4-Bump UCSP, 5-Pin SOT23, or 2mm x 2mm x 0.8mm, 6-Pin DFN Packages
MAX9938
The MAX9938 high-side current-sense amplifier offers precision accuracy specifications of V OS less than 500V (max) and gain error less than 0.5% (max). Quiescent supply current is an ultra-low 1A. The MAX9938 fits in a tiny, 1mm x 1mm UCSPTM package size or a 5-pin SOT23 package, making the part ideal for applications in notebook computers, cell phones, PDAs, and all battery-operated portable devices where accuracy, low quiescent current, and small size are critical. The MAX9938 features an input common-mode voltage range from 1.6V to 28V. These current-sense amplifiers have a voltage output and are offered in four gain versions: 25V/V (MAX9938T), 50V/V (MAX9938F), 100V/V (MAX9938H), and 200V/V (MAX9938W). The three gain selections offer flexibility in the choice of the external current-sense resistor. The very low 500V (max) input offset voltage allows small 25mV to 50mV full-scale VSENSE voltage for very low voltage drop at full-current measurement. The MAX9938 is offered in tiny 4-bump, UCSP (1mm x 1mm x 0.6mm footprint), 5-pin SOT23, and 6-pin DFN (2mm x 2mm x 0.8mm) packages specified for operation over the -40C to +85C extended temperature range.
Ordering Information
PART MAX9938TEBS+G45 MAX9938FEBS+G45 MAX9938HEBS+G45 MAX9938WEBS+G45 MAX9938TEUK+ MAX9938FEUK+ MAX9938HEUK+ MAX9938WEUK+ MAX9938FELT+ PINPACKAGE 4 UCSP 4 UCSP 4 UCSP 4 UCSP 5 SOT23 5 SOT23 5 SOT23 5 SOT23 6 DFN GAIN (V/V) 25 50 100 200 25 50 100 200 50 TOP MARK +AGD +AGE +AGF +AGI +AFFB +AFFC +AFFD +AFGZ +ACM
Applications
Cell Phones PDAs Power Management Systems Portable/Battery-Powered Systems Notebook Computers
+Denotes a lead(Pb)-free/RoHS-compliant package. G45 indicates protective die coating. Note: All devices are specified over the -40C to +85C extended temperature range.
UCSP is a trademark of Maxim Integrated Products, Inc.
Pin Configurations
TOP VIEW (BUMPS ON BOTTOM) RS+ 5 RSRS4 OUT 1 TOP VIEW (PADS ON BOTTOM)
RS+
A1
A2
6
RS-
MAX9938T/F/H/W
GND B1 B2 OUT
MAX9938T/F/H/W
N.C.
2
MAX9938FELT
5
N.C.
GND UCSP DRAWINGS NOT TO SCALE 1 GND 2 GND SOT23 3 OUT
3
4
RS+
DFN
________________________________________________________________ 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.
1A, 4-Bump UCSP/SOT23, Precision Current-Sense Amplifier MAX9938
ABSOLUTE MAXIMUM RATINGS
RS+, RS- to GND....................................................-0.3V to +30V OUT to GND .............................................................-0.3V to +6V RS+ to RS- ...........................................................................30V Short-Circuit Duration: OUT to GND ..........................Continuous Continuous Input Current (Any Pin)..................................20mA Continuous Power Dissipation (TA = +70C) 4-Bump UCSP (derate 3.0mW/C above +70C).........238mW 5-Pin SOT23 (derate 3.9mW/C above +70C)............312mW 6-Pin DFN (derate 4.5mW/C above +70C) .............358mW Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range ............................-65C to +150C Bump Temperature (soldering) Reflow............................+260C Lead Temperature (soldering, 10s) .................................+300C Soldering Temperature (reflow) .......................................+260C
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
(VRS+ = VRS- = 3.6V, VSENSE = (VRS+ - VRS-) = 0V, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER SYMBOL CONDITIONS VRS+ = 5V, TA = +25C Supply Current (Note 2) ICC VRS+ = 5V, -40C < TA < +85C VRS+ = 28V, TA = +25C VRS+ = 28V, -40C < TA < +85C Common-Mode Input Range Common-Mode Rejection Ratio Input Offset Voltage (Note 3) VCM CMRR VOS Guaranteed by CMRR , -40C < TA < +85C 1.6V < VRS+ < 28V, -40C < TA < +85C TA = +25C -40C < TA < +85C MAX9938T Gain G MAX9938F MAX9938H MAX9938W Gain Error (Note 4) Output Resistance GE ROUT TA = +25C -40C < TA < +85C (Note 5) Gain = 25 OUT Low Voltage VOL Gain = 50 Gain = 100 Gain = 200 OUT High Voltage Small-Signal Bandwidth (Note 5) Output Settling Time Power-Up Time VOH VOH = VRS- - VOUT (Note 6) VSENSE = 50mV, gain = 25 BW VSENSE = 50mV, gain = 50 VSENSE = 50mV, gain = 100 VSENSE = 50mV, gain = 200 tS tON 1% final value, VSENSE = 50mV 1% final value, VSENSE = 50mV MAX9938T/F/H MAX9938W 7.0 14.0 10 20 1.5 3 6 12 0.1 125 60 30 15 100 200 s s kHz 25 50 100 200 0.1 0.5 0.6 13.2 26.4 15 30 60 120 0.2 V mV % k V/V 1.6 94 130 100 500 600 1.1 MIN TYP 0.5 MAX 0.85 1.1 1.8 2.5 28 V dB V A UNITS
Note 1: All devices are 100% production tested at TA = +25C. All temperature limits are guaranteed by design. Note 2: VOUT = 0. ICC is the total current into RS+ plus RS- pins. 2 _______________________________________________________________________________________
1A, 4-Bump UCSP/SOT23, Precision Current-Sense Amplifier
ELECTRICAL CHARACTERISTICS (continued)
(VRS+ = VRS- = 3.6V, VSENSE = (VRS+ - VRS-) = 0V, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1) Note 3: VOS is extrapolated from measurements for the gain-error test. Note 4: Gain error is calculated by applying two values of VSENSE and calculating the error of the slope vs. the ideal: Gain = 25, VSENSE is 20mV and 120mV. Gain = 50, VSENSE is 10mV and 60mV. Gain = 100, VSENSE is 5mV and 30mV. Gain = 200, VSENSE is 2.5mV and 15mV. Note 5: The device is stable for any external capacitance value. Note 6: VOH is the voltage from VRS- to VOUT with VSENSE = 3.6V/gain.
MAX9938
Typical Operating Characteristics
(VRS+ = VRS- = 3.6V, TA = +25C, unless otherwise noted.)
SUPPLY CURRENT vs. TEMPERATURE
MAX9938 toc02 MAX9938 toc03
INPUT OFFSET VOLTAGE HISTOGRAM
MAX9938 toc01
GAIN ERROR HISTOGRAM
30 25 20 N (%) 15 10 5 0 1.4 1.2 SUPPLY CURRENT (A) 1.0 0.8
30 25 20 N (%) 15 10 5 0 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 INPUT OFFSET VOLTAGE (mV)
28V
3.6V 0.6 0.4 0.2 1.8V
-0.4 -0.3 -0.2 -0.1
0
0.1 0.2
0.3 0.4
0 -40 -15 10 35 60 85 TEMPERATURE (C)
GAIN ERROR (%)
INPUT OFFSET vs. COMMON-MODE VOLTAGE
MAX9938 toc04
INPUT OFFSET vs. TEMPERATURE
MAX9938 toc05
SUPPLY CURRENT vs. COMMON-MODE VOLTAGE
MAX9938 toc06
-30
60 50 INPUT OFFSET (V) 40 30 20 10 0
1.4 1.2 SUPPLY CURRENT (A) 1.0 0.8 0.6 0.4 0.2 0
-35 INPUT OFFSET (V)
-40
-45
-50
-55 0 5 10 15 20 25 30 SUPPLY VOLTAGE (V)
-40
-15
10
35
60
85
0
5
10
15
20
25
30
TEMPERATURE (C)
SUPPLY VOLTAGE (V)
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3
1A, 4-Bump UCSP/SOT23, Precision Current-Sense Amplifier MAX9938
Typical Operating Characteristics (continued)
(VRS+ = VRS- = 3.6V, TA = +25C, unless otherwise noted.)
GAIN ERROR vs. COMMON-MODE VOLTAGE
MAX9938 toc07
GAIN ERROR vs. TEMPERATURE
MAX9938 toc08
VOUT vs. VSENSE (SUPPLY = 3.6V)
3.5 3.0 G = 100 VOUT (V) 2.5 G = 50 2.0 1.5 1.0 0.5 0 0 50 VSENSE (mV) 100 150 G = 25
MAX9938 toc09
0.1 0 GAIN ERROR (%) -0.1 -0.2 -0.3 -0.4 -0.5 0 5 10 15 VOLTAGE (V) 20 25
0.08 0.07 0.06 GAIN ERROR (%) 0.05 0.04 0.03 0.02 0.01 0
4.0
30
-40
-15
10
35
60
85
TEMPERATURE (C)
VOUT vs. VSENSE (SUPPLY = 1.6V)
MAX9938 toc10
SMALL SIGNAL GAIN vs. FREQUENCY
AV = 25V/V 0 -5 AV = 100V/V AV = 50V/V GAIN (dB)
MAX9938 toc11
CMRR vs. FREQUENCY
-20 G = 25 -40 -60 -80 -100 -120 -140 -160 G = 100 G = 50
MAX9938 toc12
1.8 1.6 1.4 1.2 VOUT (V) 1.0 0.8 0.6 0.4 0.2 0 0 20 40 60 80 G = 100 G = 50 G = 25
5
0
GAIN (dB)
-10 -15 -20 -25 -30
100
1Hz
10Hz 100Hz
1kHz
10kHz 100kHz 1MHz
1Hz
10Hz 100Hz
1kHz
10kHz 100kHz 1MHz
VSENSE (mV)
FREQUENCY (kHz)
FREQUENCY (kHz)
SMALL-SIGNAL PULSE RESPONSE (GAIN = 100)
MAX9938 toc13a
SMALL-SIGNAL PULSE RESPONSE (GAIN = 50)
MAX9938 toc13b
15mV VSENSE 10mV VSENSE
30mV
20mV 1.5V
1.5V VOUT 1V VOUT 1V
20s/div
25s/div
4
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1A, 4-Bump UCSP/SOT23, Precision Current-Sense Amplifier
Typical Operating Characteristics (continued)
(VRS+ = VRS- = 3.6V, TA = +25C, unless otherwise noted.)
MAX9938
SMALL-SIGNAL PULSE RESPONSE (GAIN = 25)
MAX9938 toc13c
LARGE-SIGNAL PULSE RESPONSE (GAIN = 100)
MAX9938 toc14a
60mV VSENSE VSENSE 40mV 1.5V
30mV
10mV
3V VOUT VOUT 1V 1V
25s/div
20s/div
LARGE-SIGNAL PULSE RESPONSE (GAIN = 50)
MAX9938 toc14b
LARGE-SIGNAL PULSE RESPONSE (GAIN = 25)
MAX9938 toc14c
60mV VSENSE 10mV 3V VSENSE
120mV
20mV 3V
VOUT 0.5V
VOUT 0.5V
25s/div
25s/div
Pin Description
PIN UCSP A1 A2 B1 B2 -- SOT23 5 4 1, 2 3 -- DFN 4 6 3 1 2, 5 NAME RS+ RSGND OUT N.C. FUNCTION External Sense Resistor Power-Side Connection External Sense Resistor Load-Side Connection Ground Output Voltage. VOUT is proportional to VSENSE = VRS+ - VRS-. No Connection. Not internally connected.
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5
1A, 4-Bump UCSP/SOT23, Precision Current-Sense Amplifier MAX9938
Typical Operating Circuit
ILOAD RSENSE
VBATT = 1.6V TO 28V RS+ R1 R1 RS-
VDD = 3.3V
LOAD
C P
MAX9938
OUT
ADC
ROUT
10k
GND
Detailed Description
The MAX9938 unidirectional high-side, current-sense amplifier features a 1.6V to 28V input common-mode range. This feature allows the monitoring of current out of a battery with a voltage as low as 1.6V. The MAX9938 monitors current through a current-sense resistor and amplifies the voltage across that resistor. The MAX9938 is a unidirectional current-sense amplifier that has a well-established history. An op amp is used to force the current through an internal gain resistor at RS+, which has a value of R1, such that its voltage drop equals the voltage drop across an external sense resistor, RSENSE. There is an internal resistor at RS- with the
same value as R1 to minimize offset voltage. The current through R1 is sourced by a high-voltage p-channel FET. Its source current is the same as its drain current, which flows through a second gain resistor, ROUT. This produces an output voltage, VOUT, whose magnitude is I LOAD x R SENSE x R OUT /R 1 . The gain accuracy is based on the matching of the two gain resistors R1 and R OUT (see Table 1). Total gain = 25V/V for the MAX9938T, 50V/V for the MAX9938F, 100V/V for the MAX9938H, and 200V/V for the MAX9938W. The output is protected from input overdrive by use of an output current limiting circuit of 7mA (typical) and a 6V clamp protection circuit.
Table 1. Internal Gain Setting Resistors (Typical Values)
GAIN (V/V) 200 100 50 25 R1 () 100 100 200 400 ROUT (k) 20 10 10 10
6
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1A, 4-Bump UCSP/SOT23, Precision Current-Sense Amplifier
Applications Information
Choosing the Sense Resistor
Choose RSENSE based on the following criteria:
Voltage Loss A high RSENSE value causes the power-source voltage to drop due to IR loss. For minimal voltage loss, use the lowest RSENSE value. OUT Swing vs. VRS+ and VSENSE The MAX9938 is unique since the supply voltage is the input common-mode voltage (the average voltage at RS+ and RS-). There is no separate VCC supply voltage pin. Therefore, the OUT voltage swing is limited by the minimum voltage at RS+.
VOUT (max) = VRS+ (min) - VSENSE (max) - VOH and RSENSE = VOUT (max) G x I LOAD (max)
Efficiency and Power Dissipation At high current levels, the I2R losses in RSENSE can be significant. Take this into consideration when choosing the resistor value and its power dissipation (wattage) rating. Also, the sense resistor's value might drift if it is allowed to heat up excessively. The precision VOS of the MAX9938 allows the use of small sense resistors to reduce power dissipation and reduce hot spots. Kelvin Connections Because of the high currents that flow through RSENSE, take care to eliminate parasitic trace resistance from causing errors in the sense voltage. Either use a fourterminal current-sense resistor or use Kelvin (force and sense) PCB layout techniques.
MAX9938
Optional Output Filter Capacitor
When designing a system that uses a sample-and-hold stage in the ADC, the sampling capacitor momentarily loads OUT and causes a drop in the output voltage. If sampling time is very short (less than a microsecond), consider using a ceramic capacitor across OUT and GND to hold VOUT constant during sampling. This also decreases the small-signal bandwidth of the currentsense amplifier and reduces noise at OUT.
VSENSE full scale should be less than VOUT/gain at the minimum RS+ voltage. For best performance with a 3.6V supply voltage, select RSENSE to provide approximately 120mV (gain of 25V/V), 60mV (gain of 50V/V), 30mV (gain of 100V/V), or 15mV (gain of 200V/V) of sense voltage for the full-scale current in each application. These can be increased by use of a higher minimum input voltage.
Input Filters
Some applications of current-sense amplifiers need to measure currents accurately even in the presence of both differential and common-mode ripple, as well as a wide variety of input transient conditions. For example, high-frequency ripple at the output of a switching buck or boost regulator results in a common-mode voltage at the inputs of the MAX9938. Alternatively, fast load-current transients, when measuring at the input of a switching buck or boost regulator, can cause high-frequency differential sense voltages to occur at the inputs of the MAX9938, although the signal of interest is the average DC value. Such highfrequency differential sense voltages may result in a voltage offset at the MAX9938 output.
Accuracy In the linear region (VOUT < VOUT(max)), there are two components to accuracy: input offset voltage (VOS) and gain error (GE). For the MAX9938, VOS = 500V (max) and gain error is 0.5% (max). Use the linear equation:
VOUT = (gain GE) x VSENSE (gain x VOS) to calculate total error. A high RSENSE value allows lower currents to be measured more accurately because offsets are less significant when the sense voltage is larger.
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7
1A, 4-Bump UCSP/SOT23, Precision Current-Sense Amplifier
The MAX9938 allows two methods of filtering to help improve performance in the presence of input commonmode voltage and input differential voltage transients. Figure 1 shows a differential input filter. The capacitor CIN between RS+ and RS- along with the resistor RIN between the sense resistor and RS- helps filter against input differential voltages and prevents them from reaching the MAX9938. The corner frequency of this filter is determined by the choice of RIN, CIN, and the value of the input resistance at RS- (R1). See Table 1 for R1 values at the different gain options. The value of RIN should be chosen to minimize its effect on the input offset voltage due to the bias current at RS-. RIN x IBIAS contributes to the input voltage offset. IBIAS is typically 0.2A. Placing RIN at the RS- input does not affect the gain error of the device because the gain is given by the ratio between ROUT and R1 at RS+. Figure 2 shows the input common-mode filter. Again, the corner frequency of the filter is determined by the choice of RIN, CIN and is affected by R1. In this case RIN affects both gain error and input offset voltage. RIN should be smaller than R1 so that it has negligible effect on the device gain. If, for example, a filter with RIN = 10 and CIN = 1F is built, then depending upon the gain selection, the gain error is affected by either 2.5% (G = 25V/V, R1 = 400) or 5% (G = 50V/V, R1 = 200) or 10% (G = 100V/V, R1 = 100).
MAX9938
RSENSE
RSENSE
RIN LOAD CIN RS+
MAX9938
RIN
RIN LOAD
CIN RSOUT RS+
MAX9938
CIN RS-
OUT
GND
GND
Figure 1. Differential Input Filter
Figure 2. Input Common-Mode Filter
8
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1A, 4-Bump UCSP/SOT23, Precision Current-Sense Amplifier
Bidirectional Application
Battery-powered systems may require a precise bidirectional current-sense amplifier to accurately monitor the battery's charge and discharge currents. Measurements of the two separate outputs with respect to GND yields an accurate measure of the charge and discharge currents respectively (Figure 3).
UCSP Applications Information
For the latest application details on UCSP construction, dimensions, tape carrier information, PCB techniques, bump-pad layout, and recommended reflow temperature profile, as well as the latest information on reliability testing results, refer to the Application Note 1891: Wafer-Level Packaging (WLP) and Its Applications available on Maxim's website at www.maximic.com/ucsp.
MAX9938
ILOAD
RSENSE TO WALL-CUBE/ CHARGER RS+ R1 R1 RSRS+ R1 R1 RSLOAD
VBATT = 1.6V TO 28V
P
P
MAX9938
OUT ROUT
MAX9938
OUT
VDD = 3.3V
ROUT
10k
10k C GND ADC
GND
ADC
Figure 3. Bidirectional Application
Chip Information
PROCESS: BiCMOS
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9
1A, 4-Bump UCSP/SOT23, Precision Current-Sense Amplifier MAX9938
Package Information
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. Note that a "+", "#", or "-" in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. PACKAGE TYPE 2 x 2 UCSP 5 SOT23 6 DFN PACKAGE CODE B4+1 U5-2 L622+1 DOCUMENT NO. 21-0117 21-0057 21-0164
PACKAGE OUTLINE, 2x2 UCSP 21-0117 G
1 1
10
______________________________________________________________________________________
4L, UCSP 2x2.EPS
1A, 4-Bump UCSP/SOT23, Precision Current-Sense Amplifier
Package Information (continued)
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. Note that a "+", "#", or "-" in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status.
SOT-23 5L .EPS
MAX9938
______________________________________________________________________________________
11
1A, 4-Bump UCSP/SOT23, Precision Current-Sense Amplifier MAX9938
Package Information (continued)
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. Note that a "+", "#", or "-" in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. 6, 8, 10L UDFN.EPS
1 2
D
A
e
b
N
AAA AAA
E
SOLDER MASK COVERAGE
PIN 1 0.10x45
L
PIN 1 INDEX AREA SAMPLE MARKING 1 A A
L1
7
(N/2 -1) x e)
C L
C L
b A A2 A1
L e
EVEN TERMINAL
L e
ODD TERMINAL
PACKAGE OUTLINE, 6, 8, 10L uDFN, 2x2x0.80 mm
21-0164
B
12
______________________________________________________________________________________
1A, 4-Bump UCSP/SOT23, Precision Current-Sense Amplifier
Package Information (continued)
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. Note that a "+", "#", or "-" in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status.
MAX9938
COMMON DIMENSIONS SYMBOL A A1 A2 D E L L1 MIN. 0.70 0.15 0.020 1.95 1.95 0.30 NOM. 0.75 0.20 0.025 2.00 2.00 0.40 0.10 REF. MAX. 0.80 0.25 0.035 2.05 2.05 0.50
PACKAGE VARIATIONS PKG. CODE L622-1 L822-1 L1022-1 N 6 8 10 e 0.65 BSC 0.50 BSC 0.40 BSC b 0.300.05 0.250.05 0.200.03 (N/2 -1) x e 1.30 REF. 1.50 REF. 1.60 REF.
PACKAGE OUTLINE, 6, 8, 10L uDFN, 2x2x0.80 mm
21-0164
B
2
2
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13
1A, 4-Bump UCSP/SOT23, Precision Current-Sense Amplifier MAX9938
Revision History
REVISION NUMBER 0 1 2 3 REVISION DATE 4/08 9/08 2/09 10/09 Initial release Added DFN package information Added G45 designation to part number Added Input Filters section and MAX9938W to the data sheet DESCRIPTION PAGES CHANGED -- 1, 2, 4, 5, 9 1 1, 2, 6-9
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.
14 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2009 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.

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