MAXIM MAX9938FEUK

19-4110; Rev 0; 4/08
1µA, 4-Bump UCSP/SOT23,
Precision Current-Sense Amplifier
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 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 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) and 5-pin SOT23 packages,
specified for operation over the -40°C to +85°C extended temperature range.
Applications
Cell Phones
PDAs
Features
o Ultra-Low Supply Current of 1µA (max)
o Low 500µV (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
Ordering Information
PINPACKAGE
PART
GAIN (V/V)
TOP MARK
MAX9938TEBS+
4 UCSP
25
+AGD
MAX9938FEBS+
4 UCSP
50
+AGE
MAX9938HEBS+
4 UCSP
100
+AGF
MAX9938TEUK+
5 SOT23
25
+AFFB
MAX9938FEUK+
5 SOT23
50
+AFFC
100
+AFFD
MAX9938HEUK+ 5 SOT23
+Denotes a lead-free package.
Note: All devices are specified over the -40°C to +85°C
extended temperature range.
Power Management Systems
Portable/Battery-Powered Systems
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
MAX9938T/F/H
GND
B1
B2
UCSP
RS4
OUT
1
GND
2
GND
3
OUT
SOT23
________________________________________________________________ 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
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature ......................................................+150°C
Storage Temperature Range ............................-65°C to +150°C
Bump Temperature (soldering) Reflow............................+235°C
Lead Temperature (soldering, 10s) .................................+300°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
TYP
MAX
0.5
0.85
1.1
1.8
VRS+ = 5V, -40°C < TA < +85°C
1.1
VRS+ = 28V, TA = +25°C
VRS+ = 28V, -40°C < TA < +85°C
Common-Mode Input Range
Common-Mode Rejection Ratio
Input Offset Voltage (Note 3)
Gain
VCM
CMRR
VOS
G
Gain Error (Note 4)
GE
Output Resistance
ROUT
OUT Low Voltage
1.6
94
TA = +25°C
28
130
±100
-40°C < TA < +85°C
±500
±600
MAX9938T
25
MAX9938F
50
MAX9938H
100
TA = +25°C
±0.1
-40°C < TA < +85°C
±0.5
%
10
13.2
15
Gain = 50
3
30
Gain = 100
6
60
VOH = VRS- - VOUT (Note 6)
0.1
0.2
VSENSE = 50mV, gain = 25
125
VSENSE = 50mV, gain = 50
60
VSENSE = 50mV, gain = 100
30
tS
1% final value, VSENSE = 50mV
100
μs
tON
1% final value, VSENSE = 50mV
200
μs
VOL
Small-Signal Bandwidth
(Note 5)
BW
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.
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:
2
μV
V/V
±0.6
7.0
V
dB
1.5
VOH
Power-Up Time
Guaranteed by CMRR , -40°C < TA < +85°C
Gain = 25
OUT High Voltage
Output Settling Time
μA
2.5
1.6V < VRS+ < 28V, -40°C < TA < +85°C
(Note 5)
UNITS
_______________________________________________________________________________________
kΩ
mV
V
kHz
1µA, 4-Bump UCSP/SOT23,
Precision Current-Sense Amplifier
20
N (%)
15
10
10
5
5
-0.4 -0.3 -0.2 -0.1
0
0.1 0.2
0.4
1.8V
0
0.1 0.2
-40
0.3 0.4
-15
10
35
60
GAIN ERROR (%)
TEMPERATURE (°C)
INPUT OFFSET
vs. COMMON-MODE VOLTAGE
INPUT OFFSET
vs. TEMPERATURE
SUPPLY CURRENT
vs. COMMON-MODE VOLTAGE
-45
-50
40
30
20
10
5
10
15
20
25
30
1.0
0.8
0.6
0.4
0.2
0
-55
0
-40
-15
10
35
60
0
85
5
10
15
20
SUPPLY VOLTAGE (V)
TEMPERATURE (°C)
SUPPLY VOLTAGE (V)
GAIN ERROR
vs. COMMON-MODE VOLTAGE
GAIN ERROR
vs. TEMPERATURE
VOUT vs. VSENSE
(SUPPLY = 3.6V)
0.07
GAIN ERROR (%)
-0.1
-0.2
-0.3
-0.4
-0.5
10
15
VOLTAGE (V)
20
25
30
3.5
0.06
3.0
0.05
2.5
30
G = 100
0.04
G = 50
2.0
0.03
1.5
0.02
1.0
0.01
0.5
G = 25
0
0
5
4.0
VOUT (V)
0
25
MAX9938 toc09
0.08
MAX9938 toc07
0.1
85
MAX9938 toc06
1.2
SUPPLY CURRENT (μA)
50
INPUT OFFSET (μV)
-40
1.4
MAX9938 toc05
60
MAX9938 toc04
-35
0
3.6V
0.6
INPUT OFFSET VOLTAGE (mV)
-30
0
0.8
0
-0.4 -0.3 -0.2 -0.1
0.3 0.4
28V
1.0
0.2
0
0
INPUT OFFSET (μV)
15
MAX9938 toc08
N (%)
20
1.2
MAX9938 toc03
25
SUPPLY CURRENT (μA)
25
1.4
MAX9938 toc02
30
MAX9938 toc01
30
GAIN ERROR (%)
SUPPLY CURRENT
vs. TEMPERATURE
GAIN ERROR HISTOGRAM
INPUT OFFSET VOLTAGE HISTOGRAM
-40
-15
10
35
TEMPERATURE (°C)
60
85
0
50
100
150
VSENSE (mV)
_______________________________________________________________________________________
3
MAX9938
Typical Operating Characteristics
(VRS+ = VRS- = 3.6V, TA = +25°C, unless otherwise noted.)
Typical Operating Characteristics (continued)
(VRS+ = VRS- = 3.6V, TA = +25°C, unless otherwise noted.)
1.4
AV = 25V/V
0
GAIN (dB)
G = 100
G = 50
0.8
AV = 50V/V
-10
-15
-25
20
40
60
80
-160
1Hz
100
G = 100
-140
-30
0
-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
GAIN (dB)
1.6
MAX9938 toc11
5
MAX9938 toc10
1.8
1.0
CMRR
vs. FREQUENCY
SMALL SIGNAL GAIN
vs. FREQUENCY
MAX9938 toc12
VOUT vs. VSENSE
(SUPPLY = 1.6V)
VOUT (V)
MAX9938
1µA, 4-Bump UCSP/SOT23,
Precision Current-Sense Amplifier
10Hz 100Hz
1kHz
1Hz
10kHz 100kHz 1MHz
10Hz 100Hz
SMALL-SIGNAL PULSE RESPONSE
(G = 100)
1kHz
SMALL-SIGNAL PULSE RESPONSE
(G = 50)
MAX9938 toc13a
MAX9938 toc13b
15mV
30mV
VSENSE
10mV
VSENSE
20mV
1.5V
1.5V
VOUT
1V
VOUT
1V
20μs/div
25μs/div
SMALL-SIGNAL PULSE RESPONSE
(G = 25)
MAX9938 toc13c
60mV
VSENSE
40mV
1.5V
VOUT
1V
25μs/div
4
10kHz 100kHz 1MHz
FREQUENCY (kHz)
FREQUENCY (kHz)
VSENSE (mV)
_______________________________________________________________________________________
1µA, 4-Bump UCSP/SOT23,
Precision Current-Sense Amplifier
LARGE-SIGNAL PULSE RESPONSE
(G = 100)
LARGE-SIGNAL PULSE RESPONSE
(G = 50)
MAX9938 toc14a
MAX9938 toc14b
30mV
60mV
VSENSE
VSENSE
10mV
10mV
3V
3V
VOUT
VOUT
1V
0.5V
20μs/div
25μs/div
LARGE-SIGNAL PULSE RESPONSE
(G = 25)
MAX9938 toc14c
120mV
VSENSE
20mV
3V
VOUT
0.5V
25μs/div
Pin Description
PIN
NAME
FUNCTION
UCSP
SOT23
A1
5
RS+
External Sense Resistor Power-Side Connection
A2
4
RS-
External Sense Resistor Load-Side Connection
B1
1, 2
GND
Ground
B2
3
OUT
Output Voltage. VOUT is proportional to VSENSE = VRS+ - VRS-.
_______________________________________________________________________________________
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+
RS-
R1
R1
VDD = 3.3V
LOAD
μC
P
MAX9938
ROUT
OUT
ADC
10kΩ
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
Table 1. Internal Gain Setting Resistors
(Typical Values)
GAIN
(V/V)
6
R1
(Ω)
ROUT
(kΩ)
100
100
10
50
200
10
25
400
10
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:
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.
_______________________________________________________________________________________
1µA, 4-Bump UCSP/SOT23,
Precision Current-Sense Amplifier
VOUT (max) = VRS+ (min) - VSENSE (max) - VOH
and
VOUT (max)
RSENSE =
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), 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.
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:
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.
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.
_______________________________________________________________________________________
7
MAX9938
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+.
MAX9938
1µA, 4-Bump UCSP/SOT23,
Precision Current-Sense Amplifier
ILOAD
RSENSE
TO WALL-CUBE/
CHARGER
VBATT = 1.6V TO 28V
RS+
RS-
RS+
RSLOAD
R1
R1
R1
P
P
MAX9938
ROUT
R1
MAX9938
OUT
10kΩ
GND
ROUT
OUT
VDD = 3.3V
10kΩ
μC
GND
ADC
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
8
_______________________________________________________________________________________
1µA, 4-Bump UCSP/SOT23,
Precision Current-Sense Amplifier
PACKAGE TYPE
PACKAGE CODE
DOCUMENT NO.
2 x 2 UCSP
B4-1
21-0117
5 SOT23
U5-2
21-0057
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
© 2008 Maxim Integrated Products
is a registered trademark of Maxim Integrated Products, Inc.
MAX9938
Package Information
For the latest package outline information, go to www.maxim-ic.com/packages.