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19-4110; Rev 0; 4/08
1A, 4-Bump UCSP/SOT23, Precision Current-Sense Amplifier
General Description
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 three gain versions: 25V/V (MAX9938T), 50V/V (MAX9938F), and 100V/V (MAX9938H). 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) and 5-pin SOT23 packages, specified for operation over the -40C to +85C extended temperature range.
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) o Tiny 1mm x 1mm x 0.6mm, 4-Bump UCSP or 5-Pin SOT23 Package
MAX9938
Ordering Information
PART MAX9938TEBS+ MAX9938FEBS+ MAX9938HEBS+ MAX9938TEUK+ MAX9938FEUK+ PINPACKAGE 4 UCSP 4 UCSP 4 UCSP 5 SOT23 5 SOT23 GAIN (V/V) 25 50 100 25 50 100 TOP MARK +AGD +AGE +AGF +AFFB +AFFC +AFFD
Applications
Cell Phones PDAs Power Management Systems Portable/Battery-Powered Systems Notebook Computers
MAX9938HEUK+ 5 SOT23 +Denotes a lead-free package.
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 RS-
RS4
RS+
A1
A2
MAX9938T/F/H
GND B1 B2 OUT 1 GND
MAX9938T/F/H
UCSP
2 GND SOT23
3 OUT
________________________________________________________________ Maxim Integrated Products
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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 Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range ............................-65C to +150C Bump Temperature (soldering) Reflow............................+235C Lead Temperature (soldering, 10s) .................................+300C
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 Gain Error (Note 4) Output Resistance OUT Low Voltage OUT High Voltage Small-Signal Bandwidth (Note 5) Output Settling Time Power-Up Time GE ROUT VOL VOH BW tS tON TA = +25C -40C < TA < +85C (Note 5) Gain = 25 Gain = 50 Gain = 100 VOH = VRS- - VOUT (Note 6) VSENSE = 50mV, gain = 25 VSENSE = 50mV, gain = 50 VSENSE = 50mV, gain = 100 1% final value, VSENSE = 50mV 1% final value, VSENSE = 50mV 7.0 10 1.5 3 6 0.1 125 60 30 100 200 s s kHz 25 50 100 0.1 0.5 0.6 13.2 15 30 60 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: Note 2: Note 3: Note 4:
All devices are 100% production tested at TA = +25C. All temperature limits are guaranteed by design. VOUT = 0. ICC is the total current into RS+ plus RS- pins. VOS is extrapolated from measurements for the gain-error test. 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. 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.
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1A, 4-Bump UCSP/SOT23, Precision Current-Sense Amplifier
Typical Operating Characteristics
(VRS+ = VRS- = 3.6V, TA = +25C, unless otherwise noted.)
MAX9938
INPUT OFFSET VOLTAGE HISTOGRAM
MAX9938 toc01
GAIN ERROR HISTOGRAM
MAX9938 toc02
SUPPLY CURRENT vs. TEMPERATURE
MAX9938 toc03
30 25 20 N (%)
30 25 20 N (%) 15 10 5 0
1.4 1.2 SUPPLY CURRENT (A) 1.0 0.8 3.6V 0.6 0.4 0.2 0 1.8V
28V
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)
-0.4 -0.3 -0.2 -0.1
0
0.1 0.2
0.3 0.4
-40
-15
10
35
60
85
GAIN ERROR (%)
TEMPERATURE (C)
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)
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)
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1A, 4-Bump UCSP/SOT23, Precision Current-Sense Amplifier MAX9938
Typical Operating Characteristics (continued)
(VRS+ = VRS- = 3.6V, TA = +25C, unless otherwise noted.)
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 (G = 100)
MAX9938 toc13a
SMALL-SIGNAL PULSE RESPONSE (G = 50)
MAX9938 toc13b
15mV VSENSE 10mV VSENSE
30mV
20mV 1.5V
1.5V VOUT 1V VOUT
1V
20s/div
25s/div
SMALL-SIGNAL PULSE RESPONSE (G = 25)
MAX9938 toc13c
60mV
VSENSE
40mV 1.5V
VOUT 1V
25s/div
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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
LARGE-SIGNAL PULSE RESPONSE (G = 100)
MAX9938 toc14a
LARGE-SIGNAL PULSE RESPONSE (G = 50)
MAX9938 toc14b
30mV VSENSE 10mV VSENSE
60mV
10mV 3V
3V VOUT 1V VOUT 0.5V
20s/div
25s/div
LARGE-SIGNAL PULSE RESPONSE (G = 25)
MAX9938 toc14c
120mV VSENSE
20mV 3V
VOUT 0.5V
25s/div
Pin Description
PIN UCSP A1 A2 B1 B2 SOT23 5 4 1, 2 3 NAME RS+ RSGND OUT FUNCTION External Sense Resistor Power-Side Connection External Sense Resistor Load-Side Connection Ground Output Voltage. VOUT is proportional to VSENSE = VRS+ - VRS-.
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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, and 100V/V for the MAX9938H. The output is protected from input overdrive by use of an output current limiting circuit of 7mA (typical) and a 6V clamp protection circuit.
Applications Information
Choosing the Sense Resistor
Choose RSENSE based on the following criteria:
Table 1. Internal Gain Setting Resistors (Typical Values)
GAIN (V/V) 100 50 25 R1 () 100 200 400 ROUT (k) 10 10 10
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.
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1A, 4-Bump UCSP/SOT23, Precision Current-Sense Amplifier
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 VOUT (max) RSENSE = G x I LOAD (max) 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), or 30mV (gain of 100V/V) of sense voltage for the fullscale current in each application. These can be increased by use of a higher minimum input voltage.
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.
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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1A, 4-Bump UCSP/SOT23, Precision Current-Sense Amplifier 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 1. Bidirectional Application
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 1).
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 UCSP--A Wafer-Level Chip-Scale Package available on Maxim's website at www.maxim-ic.com/ucsp.
Chip Information
PROCESS: BiCMOS
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1A, 4-Bump UCSP/SOT23, Precision Current-Sense Amplifier
Package Information
For the latest package outline information, go to www.maxim-ic.com/packages. PACKAGE TYPE 2 x 2 UCSP 5 SOT23 PACKAGE CODE B4-1 U5-2 DOCUMENT NO. 21-0117 21-0057
MAX9938
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 _____________________ 9
(c) 2008 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.

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