19-4110; Rev 6; 1/11
KIT
ATION
EVALU
E
L
B
AVAILA
1µA, 4-Bump UCSP/SOT23,
Precision Current-Sense Amplifier
Features
o Ultra-Low Supply Current of 1µA (max)
o Low 500µV (max) Input Offset Voltage
o Low < 0.5% (max) Gain Error
The MAX9938 high-side current-sense amplifier offers
precision accuracy specifications of V OS less than
500μV (max) and gain error less than 0.5% (max).
Quiescent supply current is an ultra-low 1μA. The
MAX9938 fits in a tiny, 1mm x 1mm UCSP™ 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).
o Input Common Mode: +1.6V to +28V
o Voltage Output
o Four 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
µDFN Packages
The four gain selections offer flexibility in the choice of
the external current-sense resistor. The very low 500μV
(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 μDFN
(2mm x 2mm x 0.8mm) packages specified for operation
over the -40°C to +85°C extended temperature range.
Ordering Information
PINPACKAGE
PART
GAIN
(V/V)
TOP
MARK
MAX9938TEBS+G45
4 UCSP
25
+AGD
MAX9938FEBS+G45
4 UCSP
50
+AGE
MAX9938HEBS+G45
4 UCSP
100
+AGF
MAX9938WEBS+G45
4 UCSP
200
+AGI
MAX9938TEUK+
5 SOT23
25
+AFFB
Cell Phones
MAX9938FEUK+
5 SOT23
50
+AFFC
PDAs
MAX9938HEUK+
5 SOT23
100
+AFFD
MAX9938WEUK+
5 SOT23
200
+AFGZ
MAX9938FELT+
6 μDFN
50
+ACM
Applications
Power Management Systems
Portable/Battery-Powered Systems
+Denotes a lead(Pb)-free/RoHS-compliant package.
G45 indicates protective die coating.
Note: All devices are specified over the -40°C to +85°C
extended temperature range.
Notebook Computers
UCSP is a trademark of Maxim Integrated Products, Inc.
Pin Configurations
TOP VIEW
(BUMPS ON BOTTOM)
RS+
A1
A2
RS+
5
RS-
MAX9938T/F/H/W
MAX9938T/F/H/W
GND
B1
B2
UCSP
DRAWINGS NOT TO SCALE
TOP VIEW
(PADS ON BOTTOM)
RS4
OUT
1
N.C.
2
GND
3
MAX9938FELT
6
RS-
5
N.C.
4
RS+
OUT
1
GND
2
GND
SOT23
3
OUT
μDFN
________________________________________________________________ Maxim Integrated Products
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.
1
MAX9938
General Description
MAX9938
1µA, 4-Bump UCSP/SOT23,
Precision Current-Sense Amplifier
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 = +70°C)
4-Bump UCSP (derate 3.0mW/°C above +70°C).........238mW
5-Pin SOT23 (derate 3.9mW/°C above +70°C)............312mW
6-Pin μDFN (derate 4.5mW/°C above +70°C) .............358mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature ......................................................+150°C
Storage Temperature Range ............................-65°C to +150°C
Lead Temperature (excluding UCSP, soldering, 10s).....+300°C
Soldering Temperature (reflow) .......................................+260°C
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 = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
VRS+ = 5V, TA = +25°C
Supply Current (Note 2)
ICC
Common-Mode Input Range
VCM
TYP
MAX
0.5
0.85
VRS+ = 5V, -40°C < TA < +85°C
1.1
VRS+ = 28V, TA = +25°C
1.1
VRS+ = 28V, -40°C < TA < +85°C
Common-Mode Rejection Ratio
Input Offset Voltage (Note 3)
CMRR
VOS
G
1.6
1.6V < VRS+ < 28V, -40°C < TA < +85°C
94
TA = +25°C
OUT Low Voltage
OUT High Voltage
Small-Signal Bandwidth
(Note 5)
Output Settling Time
2
ROUT
50
100
VOL
VOH
BW
tS
V/V
200
TA = +25°C
±0.1
-40°C < TA < +85°C
±0.5
±0.6
TA = +25°C
±0.1
-40°C < TA < +85°C
±0.7
%
±0.8
MAX9938T/F/H
7.0
10
13.2
MAX9938W
14.0
20
26.4
Gain = 25
1.5
15
Gain = 50
3
30
Gain = 100
6
60
Gain = 200
12
120
VOH = VRS- - VOUT (Note 6)
0.1
0.2
VSENSE = 50mV, gain = 25
125
VSENSE = 50mV, gain = 50
60
VSENSE = 50mV, gain = 100
30
(Note 5)
μV
25
MAX9938H
GE
V
dB
±500
±600
MAX9938F
MAX9938W
Output Resistance
130
±100
MAX9938W
Gain Error (Note 4)
28
-40°C < TA < +85°C
MAX9938T/MAX9938F/
MAX9938H
μA
2.5
Guaranteed by CMRR , -40°C < TA < +85°C
MAX9938T
Gain
1.8
UNITS
VSENSE = 50mV, gain = 200
15
1% final value, VSENSE = 50mV
100
_______________________________________________________________________________________
kΩ
mV
V
kHz
μs
1µA, 4-Bump UCSP/SOT23,
Precision Current-Sense Amplifier
(VRS+ = VRS- = 3.6V, VSENSE = (VRS+ - VRS-) = 0V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1)
All devices are 100% production tested at TA = +25°C. 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.
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.
Note 1:
Note 2:
Note 3:
Note 4:
Typical Operating Characteristics
(VRS+ = VRS- = 3.6V, TA = +25°C, unless otherwise noted.)
20
N (%)
15
15
10
10
5
5
0
0
-0.4 -0.3 -0.2 -0.1
0
0.1 0.2
-0.4 -0.3 -0.2 -0.1
0.3 0.4
0.8
3.6V
0.6
0.4
1.8V
0
0.1 0.2
0
0.3 0.4
-40
-15
10
35
60
INPUT OFFSET VOLTAGE (mV)
GAIN ERROR (%)
TEMPERATURE (°C)
INPUT OFFSET
vs. COMMON-MODE VOLTAGE
INPUT OFFSET
vs. TEMPERATURE
SUPPLY CURRENT
vs. COMMON-MODE VOLTAGE
-40
-45
-50
40
30
20
10
5
10
15
20
SUPPLY VOLTAGE (V)
25
30
1.0
0.8
0.6
0.4
0.2
0
-55
1.2
SUPPLY CURRENT (μA)
50
INPUT OFFSET (μV)
-35
1.4
85
MAX9938 toc06
60
MAX9938 toc04
-30
0
28V
1.0
0.2
MAX9938 toc05
N (%)
20
1.2
MAX9938 toc03
25
SUPPLY CURRENT (μA)
25
1.4
MAX9938 toc02
30
MAX9938 toc01
30
INPUT OFFSET (μV)
SUPPLY CURRENT
vs. TEMPERATURE
GAIN ERROR HISTOGRAM
INPUT OFFSET VOLTAGE HISTOGRAM
0
-40
-15
10
35
TEMPERATURE (°C)
60
85
0
5
10
15
20
25
30
SUPPLY VOLTAGE (V)
_______________________________________________________________________________________
3
MAX9938
ELECTRICAL CHARACTERISTICS (continued)
Typical Operating Characteristics (continued)
(VRS+ = VRS- = 3.6V, TA = +25°C, unless otherwise noted.)
GAIN ERROR
vs. TEMPERATURE
-0.2
-0.3
-0.4
3.5
0.06
3.0
0.05
2.5
G = 100
VOUT (V)
-0.1
4.0
MAX9938 toc08
0.07
GAIN ERROR (%)
0
0.04
1.5
0.02
1.0
0.01
0.5
0
-0.5
5
10
15
20
25
-15
10
35
60
85
0
50
TEMPERATURE (°C)
VSENSE (mV)
VOUT vs. VSENSE
(SUPPLY = 1.6V)
SMALL SIGNAL GAIN
vs. FREQUENCY
CMRR
vs. FREQUENCY
1.4
AV = 25V/V
0
GAIN (dB)
G = 100
1.0
G = 50
0.8
AV = 50V/V
-10
-15
-25
40
60
80
-160
1Hz
100
G = 100
-140
-30
20
-80
-120
0.4
0
G = 50
-60
-100
-20
0.2
G = 25
-40
G = 25
0.6
-20
AV = 100V/V
-5
1.2
0
MAX9938 toc12
5
MAX9938 toc10
1.6
150
100
VOLTAGE (V)
1.8
0
G = 25
0
-40
30
CMRR (dB)
0
G = 50
2.0
0.03
MAX9938 toc11
GAIN ERROR (%)
0.08
MAX9938 toc07
0.1
VOUT vs. VSENSE
(SUPPLY = 3.6V)
MAX9938 toc09
GAIN ERROR
vs. COMMON-MODE VOLTAGE
VOUT (V)
MAX9938
1µA, 4-Bump UCSP/SOT23,
Precision Current-Sense Amplifier
10Hz 100Hz
1kHz
10kHz 100kHz 1MHz
1Hz
10Hz 100Hz
1kHz
10kHz 100kHz 1MHz
FREQUENCY (kHz)
FREQUENCY (kHz)
VSENSE (mV)
SMALL-SIGNAL PULSE RESPONSE
(GAIN = 50)
SMALL-SIGNAL PULSE RESPONSE
(GAIN = 100)
MAX9938 toc13b
MAX9938 toc13a
30mV
15mV
VSENSE
10mV
VSENSE
20mV
1.5V
1.5V
VOUT
1V
20μs/div
4
VOUT
1V
25μs/div
_______________________________________________________________________________________
1µA, 4-Bump UCSP/SOT23,
Precision Current-Sense Amplifier
SMALL-SIGNAL PULSE RESPONSE
(GAIN = 25)
LARGE-SIGNAL PULSE RESPONSE
(GAIN = 100)
MAX9938 toc13c
MAX9938 toc14a
30mV
60mV
VSENSE
VSENSE
10mV
40mV
1.5V
3V
VOUT
VOUT
1V
1V
25μs/div
20μs/div
LARGE-SIGNAL PULSE RESPONSE
(GAIN = 50)
LARGE-SIGNAL PULSE RESPONSE
(GAIN = 25)
MAX9938 toc14c
MAX9938 toc14b
120mV
60mV
VSENSE
VSENSE
10mV
20mV
3V
3V
VOUT
VOUT
0.5V
0.5V
25μs/div
25μs/div
Pin Description
PIN
NAME
FUNCTION
UCSP
SOT23
µDFN
A1
5
4
RS+
External Sense Resistor Power-Side Connection
A2
4
6
RS-
External Sense Resistor Load-Side Connection
B1
1, 2
3
GND
Ground
B2
3
1
OUT
Output Voltage. VOUT is proportional to VSENSE = VRS+ - VRS-.
—
—
2, 5
N.C.
No Connection. Not internally connected.
_______________________________________________________________________________________
5
MAX9938
Typical Operating Characteristics (continued)
(VRS+ = VRS- = 3.6V, TA = +25°C, unless otherwise noted.)
1µA, 4-Bump UCSP/SOT23,
Precision Current-Sense Amplifier
MAX9938
Typical Operating Circuit
ILOAD
RSENSE
VBATT = 1.6V TO 28V
RS+
R1
RSR1
VDD = 3.3V
LOAD
μC
P
MAX9938
ROUT
OUT
ADC
10kΩ
GND
Detailed Description
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.
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
Table 1. Internal Gain Setting Resistors (Typical Values)
6
GAIN (V/V)
R1 (Ω)
ROUT (kΩ)
200
100
20
100
100
10
50
200
10
25
400
10
_______________________________________________________________________________________
1µA, 4-Bump UCSP/SOT23,
Precision Current-Sense Amplifier
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 × 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),
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.
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 = 500μV (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.
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.
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.
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.
_______________________________________________________________________________________
7
MAX9938
Applications Information
MAX9938
1µA, 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 0.2μA.
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 = 10Ω and CIN = 1μF is built, then depending upon the gain selection, the gain error is affected by
either 2.5% (G = 25V/V, R1 = 400Ω) or 5% (G = 50V/V,
R1 = 200Ω) or 10% (G = 100V/V, R1 = 100Ω) or 10%
(G = 200V/V, R1 = 100Ω).
RSENSE
RSENSE
RIN
RIN
RIN
LOAD
LOAD
CIN
CIN
RS+
RSMAX9938
8
RS+
RS-
OUT
MAX9938
GND
Figure 1. Differential Input Filter
OUT
CIN
GND
Figure 2. Input Common-Mode Filter
_______________________________________________________________________________________
1µA, 4-Bump UCSP/SOT23,
Precision Current-Sense Amplifier
ILOAD
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.
RSENSE
TO WALL-CUBE/
CHARGER
VBATT = 1.6V TO 28V
RS+
RS-
RS+
RSLOAD
R1
R1
R1
P
P
MAX9938
ROUT
R1
10kΩ
GND
MAX9938
OUT
ROUT
OUT
VDD = 3.3V
10kΩ
μC
GND
ADC
ADC
Figure 3. Bidirectional Application
Chip Information
PROCESS: BiCMOS
_______________________________________________________________________________________
9
MAX9938
UCSP Applications Information
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).
MAX9938
1µA, 4-Bump UCSP/SOT23,
Precision Current-Sense Amplifier
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.
10
LAND
PATTERN NO.
PACKAGE TYPE
PACKAGE CODE
OUTLINE NO.
2 x 2 UCSP
B4+1
21-0117
—
5 SOT23
U5-2
21-0057
90-0174
6 μDFN
L622+1
21-0164
90-0004
______________________________________________________________________________________
1µA, 4-Bump UCSP/SOT23,
Precision Current-Sense Amplifier
SOT-23 5L .EPS
______________________________________________________________________________________
11
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.
MAX9938
1µA, 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.
12
______________________________________________________________________________________
1µA, 4-Bump UCSP/SOT23,
Precision Current-Sense Amplifier
______________________________________________________________________________________
13
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.
MAX9938
1µA, 4-Bump UCSP/SOT23,
Precision Current-Sense Amplifier
Revision History
PAGES
CHANGED
REVISION
NUMBER
REVISION
DATE
0
4/08
Initial release
1
9/08
Added μDFN package information
2
2/09
Added G45 designation to part number
3
10/09
Added Input Filters section and MAX9938W to the data sheet
4
2/10
Updated EC table and Input Filters section
5
8/10
Removed Power-Up Time parameter
2
6
1/11
Corrected error on Figure 2
8
DESCRIPTION
—
1, 2, 4, 5, 9
1
1, 2, 6–9
2, 8
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
© 2011 Maxim Integrated Products
Maxim is a registered trademark of Maxim Integrated Products, Inc.
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