General Description
The MAX9934 high-precision, low-voltage, high-side
current-sense amplifier is ideal for both bidirectional
(charge/discharge) and unidirectional current measure-
ments in battery-powered portable and laptop devices.
Input offset voltage (VOS) is a low 10µV (max) at +25°C
across the -0.1V to 5.5V input common-mode voltage
range, and is independent of VCC. Its precision input
specification allows the use of very small sense volt-
ages (typically ±10mV full-scale) for minimally invasive
current sensing.
The output of the MAX9934 is a current proportional to
input VSENSE and is available in either 25µA/mV or
5µA/mV gain options (GM) with gain accuracy better
than 0.25% (max) at +25°C. A chip select (CS) allows
multiplexing of several MAX9934 current outputs to a
single microcontroller ADC channel (see the
Typical
Operating Circuit
). CS is compatible with 1.8V and 3.3V
logic systems.
The MAX9934 is designed to operate from a 2.5V to
3.6V VCC supply, and draws just 120µA (typ) quiescent
current. When powered down (VCC = 0), RS+ and RS-
draw less than 0.1nA (typ) leakage current to reduce
battery load. The MAX9934 is robust and protected
from input faults of up to ±6V input differential voltage
between RS+ and RS-.
The MAX9934 is specified for operation over the -40°C
to +125°C temperature range and is available in an
8-pin µMAX®or a 6-bump UCSP™ (1mm x 1.5mm x
0.6mm), making it ideal for space-sensitive applications.
Applications
PDAs and Smartphones
MP3 Players
Sensor Instrumentation Amplifiers
Notebook PCs and Ultra-Mobile PCs
Portable Current Monitoring
Features
♦Input Offset Voltage: 10µV (max)
♦Gain Error Less than 0.25%
♦-0.1V to +5.5V Input Common-Mode Voltage
Range
♦Chip Select Allows Multiplexing Several MAX9934
Current Monitors to One ADC
♦Current Output Allows ROUT Selection
for Gain Flexibility
♦Single Supply Operation: 2.5V to 3.6V
♦Two Gain Options: GMof 25µA/mV (MAX9934T)
and 5µA/mV (MAX9934F)
♦Bidirectional or Unidirectional Operation
♦Small, 6-Bump UCSP (1mm x 1.5mm x 0.6mm)
and 8-Pin µMAX Packages
MAX9934
High-Precision, Low-Voltage, Current-Sense Amplifier
with Current Output and Chip Select for Multiplexing
________________________________________________________________
Maxim Integrated Products
1
19-5011; Rev 2; 4/10
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.
EVALUATION KIT
AVAILABLE
Ordering Information
PART GAIN PIN-
PACKAGE
TOP
MARK
MAX9934FART+T 5µA/mV 6 UCSP AAG
MAX9934FAUA+T 5µA/mV 8 µMAX —
MAX9934TART+T
25µA/mV
6 UCSP AAF
MAX9934TAUA+T
25µA/mV
8 µMAX —
Note: All devices are specified over the -40°C to +125°C
extended temperature range.
+
Denotes a lead(Pb)-free/RoHS-compliant package.
T = Tape and reel.
µMAX is a registered trademark and UCSP is a trademark of
Maxim Integrated Products, Inc.
ILOAD
RSENSE
RS-
RS+
-0.1V ≤ VCM ≤ 5.5V
VCC = 3.3V
VCC
CS
GND
MAX9934
OUT
ROUT
10kΩ
VOUT TO ADC
FROM μC
CHIP SELECT
1000pF
0.1μF
Typical Operating Circuit
MAX9934
High-Precision, Low-Voltage, Current-Sense Amplifier
with Current Output and Chip Select for Multiplexing
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VCC = 3.3V, VRS+ = VRS- = 3.0V, VSENSE = 0V, VCM = (VRS+ + VRS-)/2, VCS = 3.3V, ROUT = 10kΩto GND for unidirectional opera-
tion, ROUT = 10kΩto VCC/2 for bidirectional operation. TA= -40°C to +125°C, unless otherwise noted. Typical values are at TA=
+25°C.) (Note 2)
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.
RS+, RS- to GND......................................................-0.3V to +6V
VCC to GND..............................................................-0.3V to +4V
CS, OUT to GND (VCC = 0, or CS < VIL)..................-0.3V to +4V
OUT to GND (CS > VIH)................................-0.3V to VCC + 0.3V
Differential Input Voltage (RS+ - RS-) ....................................±6V
Output Short-Circuit Current Duration
OUT to GND or VCC ...............................................Continuous
Continuous Input Current into Any Terminal.....................±20mA
Continuous Power Dissipation (TA= +70°C)
8-Pin µMAX (derate multilayer 4.8mW/°C
above +70°C).............................................................388mW
Junction-to-Ambient Thermal Resistance (θJA)
(Note 1) ....................................................................206°C/W
Junction-to-Case Thermal Resistance (θJC)
(Note 1) ......................................................................42°C/W
6-Bump UCSP (derate multilayer 3.9mW/°C
above +70°C).............................................................308mW
Junction-to-Ambient Thermal Resistance (θJA)
(Note 1) ....................................................................260°C/W
Operating Temperature Range .........................-40°C to +125°C
Junction Temperature......................................................+150°C
Storage Temperature Range .............................-65°C to +160°C
Lead Temperature (µMAX only, soldering, 10s) ..............+300°C
Soldering Temperature (reflow) .......................................+260°C
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
DC CHARACTERISTICS
TA = +25°C ±10
MAX9934T -40°C ≤ TA ≤ +125°C ±14
TA = +25°C ±10
Input Offset Voltage (Note 3) VOS
MAX9934F -40°C ≤ TA ≤ +125°C ±20
µV
MAX9934T ±60
Input Offset Voltage Drift (Note 3) VOS/dT MAX9934F ±90 nV/°C
Common-Mode Input Voltage
Range (Average of VRS+ and
VRS-) (Note 3)
CMVR Guaranteed by CMRR2 -0.1 +5.5 V
TA = +25°C 128 134
0 ≤ VCM ≤ VCC -
0.2V (MAX9934F) -40°C ≤ TA ≤ +125°C 112
TA = +25°C 128 135
CMRR1
0 ≤ VCM ≤ VCC -
0.2V (MAX9934T) -40°C ≤ TA ≤ +125°C 109
TA = +25°C 119 125
-0.1 ≤ VCM ≤ 5.5V
(MAX9934F) -40°C ≤ TA ≤ +125°C 104
TA = +25°C 98 113
Common-Mode Rejection Ratio
(Note 3)
CMRR2
-0.1 ≤ VCM ≤ 5.5V
(MAX9934T) -40°C ≤ TA ≤ +125°C 98
dB
Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-
layer board. For detailed information on package thermal considerations, refer to www.maxim-ic.com/thermal-tutorial.
MAX9934
High-Precision, Low-Voltage, Current-Sense Amplifier
with Current Output and Chip Select for Multiplexing
_______________________________________________________________________________________ 3
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
MAX9934T 25
Current Gain (Transconductance) GMMAX9934F 5 µA/mV
TA = +25°C ±0.25
MAX9934T -40°C ≤ TA ≤ +125°C ±2.0
TA = +25°C ±0.25
Current Gain Error
(Note 4) GME
MAX9934F -40°C ≤ TA ≤ +125°C ±2.4
%
MAX9934T ±200
Gain Error Drift GME/dT MAX9934F ±240 ppm/°C
Input-Bias Current for RS+ IBRS+ VRS+ = VRS- = 5.5V 0.1 100 nA
VRS+ = VRS- ≤ VCC - 0.2V 0.1 100 nA
Input-Bias Current for RS- IBRS- VRS+ = VRS- = 5.5V 35 60 µA
Input Leakage Current ILEK VCC = 0V, VRS+ = VRS- = 5.5V 0.1 100 nA
DC CHARACTERISTICS
Minimum Current for Output Low IOL Unidirectional, VOL = IOL x ROUT 1 100 nA
VOH IOUT = +600µA, VOH = VCC - VOUT 0.1 0.25
Output-Voltage Range
(MAX9934T) VOL IOUT = -600µA, bidirectional 0.15 0.25 V
VOH IOUT = +375µA, VOH = VCC - VOUT 0.18 0.30
Output-Voltage Range
(MAX9934F) VOL IOUT = -375µA, bidirectional 0.18 0.26 V
Deselected Amplifier Output
Leakage IOLK VCS = 0V, VOUT = 3.6V,
and 0 ≤ VCC ≤ 3.6V 0.1 100 nA
LOGIC I/O (CS)
Input Voltage Low CS VIL 0.54 V
Input Voltage High CS VIH 1.26 V
Input Current CS IIL,IIH 0 ≤ VCS ≤ VCC 0.1 100 nA
POWER SUPPLY
Supply-Voltage Range VCC Guaranteed by PSRR 2.5 3.6 V
Power-Supply Rejection Ratio PSRR 2.5V ≤ VCC ≤ 3.6V,
VRS+ = VRS- = 2V (Note 3) 110 120 dB
Supply Current ICC VCC = 3.3V, ROUT = 10kΩ to 3.3V,
VRS+ = VRS- = 3.1V 120 230 µA
Supply Current, Output
Deselected ICC
,
DES VCS = 0V, ROUT = 10kΩ to 3.3V,
VRS+ = VRS- = 3.1V 120 210 µA
AC CHARACTERISTICS (CL = 1000pF)
MAX9934T
GM = 25µA/mV, VSENSE = 5mV 1.5
Amplifier Bandwidth BW
MAX9934F
GM = 5µA/mV, VSENSE = 25mV 5
kHz
ELECTRICAL CHARACTERISTICS (continued)
(VCC = 3.3V, VRS+ = VRS- = 3.0V, VSENSE = 0V, VCM = (VRS+ + VRS-)/2, VCS = 3.3V, ROUT = 10kΩto GND for unidirectional opera-
tion, ROUT = 10kΩto VCC/2 for bidirectional operation. TA= -40°C to +125°C, unless otherwise noted. Typical values are at TA=
+25°C.) (Note 2)
MAX9934
High-Precision, Low-Voltage, Current-Sense Amplifier
with Current Output and Chip Select for Multiplexing
4 _______________________________________________________________________________________
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
0.1% final value, Figure 1, MAX9934T 670
Output Settling Time tS0.1% final value, Figure 1, MAX9934F 220 µs
Output to 0.1% final value, Figure 2,
MAX9934T 150
Output Select Time tZH Output to 0.1% final value, Figure 2,
MAX9934F 80
µs
Output Deselect Time tHZ Output step of 100mV, CL = 10pF,
Figure 2 2µs
Power-Down Time tPD Output step of -100mV, CL = 10pF,
VCC > 2.5V 2µs
0.1% final value, Figure 3, MAX9934T 300
Power-Up Time tPU 0.1% final value, Figure 3, MAX9934F 200 µs
ELECTRICAL CHARACTERISTICS (continued)
(VCC = 3.3V, VRS+ = VRS- = 3.0V, VSENSE = 0V, VCM = (VRS+ + VRS-)/2, VCS = 3.3V, ROUT = 10kΩto GND for unidirectional opera-
tion, ROUT = 10kΩto VCC/2 for bidirectional operation. TA= -40°C to +125°C, unless otherwise noted. Typical values are at TA=
+25°C.) (Note 2)
Note 2: All devices are 100% production tested at TA= +25°C. Unless otherwise noted, specifications overtemperature are guaran-
teed by design.
Note 3: Guaranteed by design. Thermocouple, contact resistance, RS- input-bias current, and leakage effects preclude measure-
ment of this parameter during production testing. Devices are screened during production testing to eliminate defective
units.
Note 4: Gain error tested in unidirectional mode: 0.2V ≤VOUT ≤3.1V for the MAX9934T; 0.25V ≤VOUT ≤2.5V for the MAX9934F.
MAX9934
High-Precision, Low-Voltage, Current-Sense Amplifier
with Current Output and Chip Select for Multiplexing
_______________________________________________________________________________________
5
Typical Operating Characteristics
(VCC = 3.3V, VRS+ = VRS- = 3.0V, VSENSE = 0V, CL= 1000pF, ROUT = 10kΩto GND for unidirectional operation, ROUT = 10kΩto
VCC/2 for bidirectional operation. TA= +25°C, unless otherwise noted.)
MAX9934T VOS HISTOGRAM
MAX9934 toc01
VOS (FV)
N (%)
-8 -6 -4 -2 0 2 4 6 8
5
10
15
20
25
30
35
40
0
-10 10
OFFSET VOLTAGE
vs. COMMON-MODE VOLTAGE
MAX9934 toc04
COMMON-MODE VOLTAGE (V)
OFFSET VOLTAGE (FV)
4.84.12.7 3.41.3 2.00.6
-8
-6
-4
-2
0
2
4
6
8
10
-10
-0.15.5
VCC = 3.3V
VCC = 3.6V
VCC = 2.5V
MAX9934T DRIFT VOS HISTOGRAM
MAX9934 toc02
TCVOS (nV/NC)
N (%)
6 1218243036424854
5
10
15
20
25
30
0
060
OFFSET VOLTAGE
vs. COMMON-MODE VOLTAGE
MAX9934 toc03
COMMON-MODE VOLTAGE (V)
OFFSET VOLTAGE (FV)
4.84.12.7 3.41.3 2.00.6
-8
-6
-4
-2
0
2
4
6
8
10
-10
-0.15.5
TA = +125NC
TA = +25NC
TA = -40NC
0
0.5
1.5
1.0
2.5
3.0
2.0
3.5
0203010 40 50 60 70 80
VOUT vs. VSENSE
VREF = GND
MAX9934 toc09
VSENSE (mV)
VOUT (V)
GAIN = 25µA/mV
GAIN = 5µA/mV
UNIDIRECTIONAL
5
10
15
20
25
30
0
-0.16
-0.12
-0.08
-0.04
0
0.04
0.08
0.12
0.16
-0.20
0.20
MAX9934T GAIN ERROR
HISTOGRAM
MAX9934 toc05
GE (%)
N (%)
5
10
15
20
25
30
35
0
-160
-120
-80
-40
0
40
80
120
160
-200
200
MAX9934T GAIN ERROR
DRIFT HISTOGRAM
MAX9934 toc06
TC GE (PPM/NC)
N (%)
5
10
15
20
25
30
35
40
0
-0.16
-0.12
-0.08
-0.04
0
0.04
0.08
0.12
0.16
-0.20
0.20
MAX9934F GAIN ERROR
HISTOGRAM
MAX9934 toc07
GE (%)
N (%)
-160
-120
-80
-40
0
40
80
120
160
-200
200
MAX9934F GAIN ERROR DRIFT
HISTOGRAM
MAX9934 toc08
TC GE (PPM/°C)
N (%)
5
10
15
20
25
0
MAX9934
High-Precision, Low-Voltage, Current-Sense Amplifier
with Current Output and Chip Select for Multiplexing
6 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(VCC = 3.3V, VRS+ = VRS- = 3.0V, VSENSE = 0V, CL= 1000pF, ROUT = 10kΩto GND for unidirectional operation, ROUT = 10kΩto
VCC/2 for bidirectional operation. TA= +25°C, unless otherwise noted.)
-2.0
-0.5
-1.0
-1.5
0.5
0
1.5
1.0
2.0
VOUT vs. VSENSE
VREF = 1.65V
MAX9934 toc10
VSENSE (mV)
VOUT - VREF (V)
-40 -20 0 20 40
GAIN = 25µA/mV
GAIN = 5µA/mV
BIDIRECTIONAL
VOUT vs. VSENSE (VOUT < 5mV)
MAX9934 toc11
VSENSE + VOS (FV)
VOUT (mV)
80604020
1
2
3
4
5
0
0100
G = 25FA/mV
G = 5FA/mV
0
100
50
200
150
250
300
0 200 300100 400 500 600
VOH vs. IOH
MAX9934 toc12
IOH (µA)
VOH (mV)
MAX9934F
MAX9934T
40
80
60
120
100
140
160
-40 -10 5 20-25 35 50 65 80 95 110 125
SUPPLY CURRENT
vs. TEMPERATURE (VCS = 0)
MAX9934 toc13
TEMPERATURE (°C)
SUPPLY CURRENT (µA)
VCM = 0V
VCM = 5.5V
40
80
60
120
100
140
160
-40 -10 5 20-25 35 50 65 80 95 110 125
SUPPLY CURRENT
vs. TEMPERATURE
MAX9934 toc14
TEMPERATURE (°C)
SUPPLY CURRENT (µA)
VCM = 0V
VCM = 5.5V
MAX9934
High-Precision, Low-Voltage, Current-Sense Amplifier
with Current Output and Chip Select for Multiplexing
_______________________________________________________________________________________ 7
Typical Operating Characteristics (continued)
(VCC = 3.3V, VRS+ = VRS- = 3.0V, VSENSE = 0V, CL= 1000pF, ROUT = 10kΩto GND for unidirectional operation, ROUT = 10kΩto
VCC/2 for bidirectional operation. TA= +25°C, unless otherwise noted.)
NORMALIZED GAIN
vs. FREQUENCY
MAX9934 toc20
FREQUENCY (Hz)
NORMALIZED GAIN (dB)
10k1k10010
-30
-20
-10
0
10
-40
1 100k
G = 5FA/mV
G = 25FA/mV
COMMON-MODE REJECTION RATIO
vs. FREQUENCY
MAX9934 toc21
FREQUENCY (kHz)
CMRR (dB)
101.00.1
-120
-100
-80
-60
-40
-20
0
-140
0.01 100
MAX9934
High-Precision, Low-Voltage, Current-Sense Amplifier
with Current Output and Chip Select for Multiplexing
8 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(VCC = 3.3V, VRS+ = VRS- = 3.0V, VSENSE = 0V, CL= 1000pF, ROUT = 10kΩto GND for unidirectional operation, ROUT = 10kΩto
VCC/2 for bidirectional operation. TA= +25°C, unless otherwise noted.)
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
MAX9934 toc22
FREQUENCY (kHz)
PSRR (dB)
101.00.1
-100
-80
-60
-40
-20
0
-120
0.01 100
OUTPUT SETTING TIME
vs. PERCENTAGE OF FINAL VALUE
MAX9934 toc23
PERCENTAGE OF FINAL VALUE (%)
SETTING TIME (ms)
0.10
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0
1.00 0.01
±1V VOUT STEP
MAX9934T
MAX9934F
400µs/div
LARGE-SIGNAL INPUT STEP
RESPONSE (MAX9934T)
VSENSE
5mV/div
VOUT
500mV/div
MAX9934 toc25
0.01% FINAL VALUE
1% FINAL VALUE
2V
1V
MAX9934 toc26
1V
1V
40Fs/div
VCS
2V/div
VOUT
500mV/div
VOUT
500mV/div
1% FINAL VALUE
0.1% FINAL VALUE
0.1% FINAL VALUE
MAX9934T
MAX9934F
1% FINAL VALUE
OUTPUT SELECT TIME
MAX9934
High-Precision, Low-Voltage, Current-Sense Amplifier
with Current Output and Chip Select for Multiplexing
_______________________________________________________________________________________ 9
Typical Operating Characteristics (continued)
(VCC = 3.3V, VRS+ = VRS- = 3.0V, VSENSE = 0V, CL= 1000pF, ROUT = 10kΩto GND for unidirectional operation, ROUT = 10kΩto
VCC/2 for bidirectional operation. TA= +25°C, unless otherwise noted.)
POWER-UP TIME
MAX9934 toc28
1V
1V
100Fs/div
VCS
2V/div
VOUT
500mV/div
VOUT
500mV/div
MAX9934T
MAX9934F
1% FINAL VALUE
0.1% FINAL VALUE
CBYPASS = 0.1µF
1% FINAL VALUE
0.1% FINAL VALUE
SATURATION RECOVERY TIME
VOUT = VOL TO 1V (MAX9934T)
MAX9934 toc29
1mV
0V
1V
UNIDIRECTIONAL
400Fs/div
VSENSE
5mV/div
VOUT
500mV/div
400µs/div
SATURATION RECOVERY TIME
VOUT = VOH TO 1V (MAX9934T)
VSENSE
10mV/div
VOUT
1V/div
MAX9934 toc30
1V
UNIDIRECTIONAL
MAX9934
Detailed Description
The MAX9934 high-side, current-sense amplifier moni-
tors current through an external current-sense resistor
by amplifying the voltage across the resistor (VSENSE)
to create an output current (IOUT). An output voltage
(VOUT) then develops across the external output resis-
tor (ROUT). See the
Typical Operating Circuit
.
The MAX9934 uses precision amplifier design tech-
niques to achieve a low-input offset voltage of less than
10µV. These techniques also enable extremely low-input
offset voltage drift over time and temperature and
achieve gain error of less than 0.25%. The precision VOS
specification allows accurate current measurements with
a low-value current-sense resistor, thus reducing power
dissipation in battery-powered systems, as well as load-
regulation issues in low-voltage DC power supplies.
The MAX9934 high-side current-sense amplifier fea-
tures a -0.1V to +5.5V input common-mode range that
is independent of supply voltage (VCC). This ability to
sense at voltages beyond the supply rail allows the
monitoring of currents out of a power supply even in a
shorted condition, while also enabling high-side current
sensing at voltages greater than the MAX9934 supply
High-Precision, Low-Voltage, Current-Sense Amplifier
with Current Output and Chip Select for Multiplexing
10 ______________________________________________________________________________________
Pin Description
PIN/BUMP
UCSP µMAX NAME FUNCTION
A1 1 VCC Power Supply
A2 2 OUT
Current Output. OUT provides an output current proportional to input VSENSE. Connect an
external resistor (ROUT) from OUT to GND for unidirectional sensing or to an external reference
voltage for bidirectional sensing.
A3 3 GND Ground
B1 8 RS+ Sense Resistor Power Side Connection
B2 7 RS- Sense Resistor Load Side Connection
B3 6 CS Chip-Select Input. Drive CS high to enable OUT, drive CS low to put OUT in a high-impedance
state.
— 4, 5 N.C. No Connection. Not internally connected.
% FINAL VALUE
V
OUT
±1V STEP
t
S
2V
1V
t
S
% FINAL VALUE
V
SENSE
Figure 1. Output Settling Time
CS
OUT
GND
RS-
RS+
VCC
*RGAIN
Gm
MAX9934
Gm
*RGAIN = 40Ω FOR THE MAX9934T AND
RGAIN = 200Ω FOR THE MAX9934F.
Functional Diagram
voltage. Further, when VCC = 0, the amplifier maintains
an extremely high impedance on both its inputs and
output, up to the maximum operating voltages (see the
Absolute Maximum Ratings
section).
The MAX9934 features a CS that can be used to dese-
lect its output current-source. This allows multiple cur-
rent-sense amplifier outputs to be multiplexed into a
single ADC channel with a single ROUT. See the
Chip
Select Functionality for Multiplexed Systems
section for
more details.
The
Functional Diagram
shows the internal operation of
the MAX9934. At its core is the indirect current-feed-
back architecture. This architecture uses two matched
transconductance amplifiers to convert their input dif-
ferential voltages into an output current. A high-gain
feedback amplifier forces the voltage drop across
RGAIN to be the same as the input differential voltage.
The internal resistor (RGAIN) sets the transconductance
gain of the device. Both input and output transconduc-
tance amplifiers feature excellent common-mode rejec-
tion characteristics, helping the MAX9934 to deliver
industry-leading precision specifications over the full
common-mode range.
Applications Information
Advantages of Current-Output
Architecture
The transconductance transfer function of the MAX9934
converts input differential voltage to an output current.
An output termination resistor, ROUT, then converts this
current to a voltage. In a large circuit board with multi-
ple ground planes and multiple current-measurement
rails spread across the board, traditional voltage-output
current-sense amplifiers become susceptible to
ground-bounce errors. These errors occur because the
local ground at the location of the current-sense amplifi-
er is at a slightly different voltage than the local ground
voltage at the ADC that is sampling the voltage. The
MAX9934 allows accurate measurements to be made
even in the presence of system ground noise. This is
achieved by sending the output information as a cur-
rent, and by terminating to the ADC ground.
A further advantage of current-output systems is the
flexibility in setting final voltage gain of the device.
Since the final voltage gain is user-controlled by the
choice of output termination resistor, it is easy to opti-
mize the monitored load current range to the ADC input
voltage range. It is no longer necessary to increase the
size of the sense resistor (also increasing power dissi-
pation) as necessary with fixed-gain, voltage-output
current-sense amplifiers.
MAX9934
High-Precision, Low-Voltage, Current-Sense Amplifier
with Current Output and Chip Select for Multiplexing
______________________________________________________________________________________ 11
100mV
tHZ
% FINAL VALUE
tZH
VOUT
0V
1.8V
VCS
Figure 2. Output Select and Deselect Time
100mV
tPD
% FINAL VALUE
tPU
VCC
VOUT
0V
3.3V
2.5V
Figure 3. Output Power-Up and Power-Down Time
MAX9934
Chip-Select Functionality
for Multiplexed Systems
The MAX9934 features a CS that can be used to dese-
lect the output current - source achieving a high-imped-
ance output with 0.1nA leakage current. Thus, different
supply voltages can be used to power different
MAX9934 devices that are multiplexed on the same
bus. This technique makes it possible for advanced
current monitoring and power-management schemes to
be implemented when a limited number of ADC chan-
nels are available.
In a multiplexed arrangement, each MAX9934 is typi-
cally placed near the load being monitored and all
amplifier outputs are connected in common to a single
load resistor located adjacent to the monitoring ADC.
This resistor is terminated to the ADC ground reference
as shown in Figure 4 for unidirectional applications.
Figure 5 shows a bidirectional multiplexed application.
Terminating the external resistor at the ground refer-
ence of the ADC minimizes errors due to ground shift
as discussed in the
Advantages of Current-Output
Architecture
section.
The MAX9934 is capable of both sourcing and sinking
current from OUT, and thus can be used as a precision
bidirectional current-sense amplifier. To enable this
functionality, terminate ROUT to a midrail voltage VBIAS.
High-Precision, Low-Voltage, Current-Sense Amplifier
with Current Output and Chip Select for Multiplexing
12 ______________________________________________________________________________________
VCC = 3.3V
VCC = 3.3V
VCC = 3.3V
RSENSE
-0.1V ≤ VCM ≤ 5.5V
RSENSE
-0.1V ≤ VCM ≤ 5.5V
RSENSE
-0.1V ≤ VCM ≤ 5.5V
MAX9934
MAX9934
MAX9934
10kΩ
(OPTIONAL)
ADC
CS3
CS2
CS1
MICROCONTROLLER
VIN1
VIN2
VIN3
ILOAD3
ILOAD2
ILOAD1
VOUT
0.1µF
0.1µF
0.1µF
OUT3
OUT2
OUT1
UNIDIRECTIONAL OPERATION
Figure 4. Typical Application Circuit Showing Chip-Select Multiplexing
In Figure 5, VOUT is equal to VBIAS when the sum of all
outputs is zero. For positive input-sense voltages, the
MAX9934 sources current causing its output voltage to
rise above VBIAS. For negative input-sense voltages,
the MAX9934 sinks current causing its output voltage to
be lower than VBIAS, thus allowing bidirectional current
sensing.
Since the ADC reference voltage, VREF, determines the
full-scale reading, a common choice for VBIAS is
VREF/2. The current output makes it possible to use a
simple resistor-divider from VREF to GND to generate
VBIAS. The output resistance for gain calculation is the
parallel combination of the two resistors. For example, if
two equal value resistors, R, are used to generate a
VBIAS = VREF/2, the output termination resistance for
gain calculation is ROUT = R/2. See Figure 5.
MAX9934
High-Precision, Low-Voltage, Current-Sense Amplifier
with Current Output and Chip Select for Multiplexing
______________________________________________________________________________________ 13
VCC = 3.3V
VCC = 3.3V
VCC = 3.3V
RSENSE
-0.1V ≤ VCM ≤ 5.5V
RSENSE
-0.1V ≤ VCM ≤ 5.5V
RSENSE
-0.1V ≤ VCM ≤ 5.5V
MAX9934
MAX9934
MAX9934
R
10kΩ
ADC
VREF
CS2
CS1
MICROCONTROLLER
CS
CS
CS
TO EXTERNAL
REFERENCE
VOLTAGE
10kΩ
R
CS3
(OPTIONAL)
VIN1
VIN2
VIN3
ILOAD3
ILOAD2
ILOAD1
VOUT
OUT3
OUT2
OUT1
ROUT = R
2
Figure 5. Bidirectional Multiplexed Operation
MAX9934
A MAX9934 can be deselected by either forcing VCS
low as shown in Figures 4 and 5, or by making VCC =
0V as shown in Figure 6. In all these conditions, the
MAX9934 maintains a high-impedance output with
0.1nA (typ) leakage current. In this state, OUT can rise
above VCC if necessary. Thus, different supply voltages
can be used to power different MAX9934 devices that
are multiplexed on the same OUT bus. Multiplexing by
forcing the MAX9934 to be powered down (VCC = 0V)
reduces its supply current to zero to help extend bat-
tery life in portable applications.
Choosing RSENSE and ROUT
In the current-sense application, the monitored load
current (ILOAD) develops a sense voltage (VSENSE)
across a current-sense resistor (RSENSE). The
MAX9934 sources or sinks an output current that is pro-
portional to VSENSE. Finally, the MAX9934 output cur-
rent is provided to an output resistor (ROUT) to develop
an output voltage across ROUT that is proportional to
the sensed load current.
High-Precision, Low-Voltage, Current-Sense Amplifier
with Current Output and Chip Select for Multiplexing
14 ______________________________________________________________________________________
VCC = 3.3V
RSENSE
-0.1V ≤ VCM ≤ 5.5V
MAX9934
ROUT
10kΩ
(OPTIONAL)
ADC
CS2
CS1
MICROCONTROLLER
CS
CS3
VCC = 3.3V
RSENSE
-0.1V ≤ VCM ≤ 5.5V
MAX9934
CS
VCC = 3.3V
RSENSE
-0.1V ≤ VCM ≤ 5.5V
MAX9934
CS
1/4 MAX4737
1/4 MAX4737
1/4 MAX4737
VIN1
VIN2
VIN3
ILOAD1
OUT3
OUT2
OUT1
0.1µF
0.1µF
0.1µF
ILOAD3
ILOAD2
Figure 6. Multiplexed Amplifiers with Power Saving
Three components are to be selected to optimize the
current-sense system: RSENSE, ROUT, and the
MAX9934 gain option (GM= 25µA/mV or 5µA/mV).
Tables 1 and 2 are gain tables for unidirectional and
bidirectional operation, respectively. They offer a few
examples for both MAX9934 options having an output
range of 3.1V unidirectional and ±1.65V bidirectional.
Note that the output current of the MAX9934 adds to its
quiescent current. This can be calculated as follows:
IOUT,MAX = VOUT,MAX/ROUT
When selecting RSENSE, consider the expected magni-
tude of ILOAD and the required VSENSE to manage
power dissipation in RSENSE:
RSENSE = VSENSE,MAX/ILOAD,MAX
RSENSE is typically a low-value resistor specifically
designed for current-sense applications.
Finally, in selecting the appropriate MAX9934 gain option
(GM), consider both the required VSENSE and IOUT:
GM= IOUT,MAX/VSENSE,MAX
Once all three component values have been selected in
the current-sense application, the system performance
is represented by:
VSENSE = RSENSE x ILOAD
and
VOUT = VSENSE x GMx ROUT
Accuracy
In a first-order analysis of accuracy there are two
MAX9934 specifications that contribute to output error,
input offset (VOS) and gain error (GE). The MAX9934 has
a maximum VOS of 10µV and a maximum GE of 0.25%.
Note that the tolerance and temperature coefficient of
the chosen resistors directly affect the precision of any
measurement system.
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 drifts if it is
allowed to self-heat excessively. The precision VOS of
the MAX9934 allows the use of a small sense resistor to
reduce power dissipation and eliminate hot spots.
Kelvin Contacts
Due to the high currents that flow through RSENSE, take
care to prevent trace resistance in the load current path
from causing errors in the sense voltage. Use a four ter-
minal current-sense resistor or Kelvin contacts (force
and sense) PCB layout techniques.
Interfacing the MAX9934 to SAR ADCs
Since the MAX9934 is essentially a high-output imped-
ance current-source, its output termination resistor,
ROUT, acts like a source impedance when driving an
ADC channel. Most successive approximation register
(SAR) architecture ADCs specify a maximum source
resistance to avoid compromising the accuracy of their
readings. Choose the output termination resistor ROUT
such that it is less than that required by the ADC speci-
fication (10kΩor less). If the ROUT is larger than the
source resistance specified, the ADC internal sampling
capacitor can momentarily load the amplifier output
and cause a drop in the voltage reading.
If ROUT is larger than the source resistance specified,
consider using a ceramic capacitor from ADC input to
GND. This input capacitor supplies momentary charge
to the internal ADC sampling capacitor, helping hold
VOUT constant to within ±1/2 LSB during the acquisition
period. Use of this capacitor reduces the noise in the
output signal to improve sensitivity of measurement.
MAX9934
High-Precision, Low-Voltage, Current-Sense Amplifier
with Current Output and Chip Select for Multiplexing
______________________________________________________________________________________ 15
PART VSENSE
(mV)
OUTPUT
CURRENT
(µA)
ROUT
(kΩ)
GAIN
(V/V)
12.4 310 10 250
MAX9934T 24.8 620 5 125
62 310 10 50
MAX9934F 75 375 8 40
Table 1. Unidirectional Gain Table*
*
All calculations were made with VCC = 3.3V and VOUT(MAX) =
VCC - VOH = 3.1V.
PART VSENSE
(mV)
OUTPUT
CURRENT
(µA)
ROUT
(kΩ)GAIN (V/V)
±5.8 ±145 10 250
±11.6 ±290 5 125
MAX9934T
±24 ±600 2.4 60
±29 ±145 10 50
±58 ±290 5 25
MAX9934F
±72 ±360 4 20
Table 2. Bidirectional Gain Table*
*
All calculations were made with VCC = 3.3V, VOUT(MAX) = VCC -
VOH = 3.1V, VOUT(MIN) = VOL, and OUT connected to an exter-
nal reference voltage of VREF = 1.65V through ROUT.
MAX9934
Effect of Input-Bias Currents
The MAX9934 has extremely low CMOS input-bias cur-
rents at both RS+ and RS- (0.1nA) when the input com-
mon-mode voltage is less than the supply voltage.
When the input common-mode voltage becomes higher
than the supply voltage, it draws the input stage operat-
ing current from RS-, 35µA (typ). RS+ maintains its
CMOS input characteristics.
Low-input-bias currents are extremely useful in design
of input filters for current-sense amplifiers. Input differ-
ential filters are sometimes required to average out
rapidly varying load currents. An example of such load
currents are those consumed by a processor, or
switching power supply. Large bias and offset currents
can interact with resistors used in these external filters
to generate large input offset voltages and gain errors.
For more detailed information, see Application Note
AN3888:
Performance of Current-Sense Amplifiers with
Input Series Resistors
.
Due to the low-input-bias currents, resistors as large as
10kΩcan be easily used without impact on error speci-
fications with the MAX9934. For applications where the
input common-mode voltage is below VCC, a balanced
differential filter can be used. For applications where
the input common-mode voltage extends above VCC,
use a one-sided filter with a capacitor between RS+
and RS-, and a filter resistor in series with RS+ to main-
tain the excellent performance of the MAX9934. See
Figure 7.
PCB Layout
For applications where the input common-mode voltage
extends above VCC, trace resistance between RSENSE
and RS- influences the effective VOS error due to the
voltage drop developed across the trace resistance by
the 35µA input bias current at RS-.
Monitoring Very Low Currents
The accuracy of the MAX9934 leads to a wide dynamic
range. This applies to both unidirectional mode and
bidirectional mode. This is made possible in the unidi-
rectional mode because the output maintains gain
accuracy below 1mV as shown in the VOUT vs. VSENSE
(VOUT < 5mV) graph in the
Typical Operating Char-
acteristics
. Extending the useful output below 1mV
makes it possible for the MAX9934 to accurately moni-
tor very low currents.
Use as Precision
Instrumentation Amplifier
When the input common-mode voltage is below VCC,
the input bias current of the RS- input drops to the
10pA range, the same range as the RS+ input. This
low-input-bias current in combination with the rail-to-rail
common-mode input range, the extremely high com-
mon-mode rejection, and low VOS of the MAX9934
make it ideally suited for use as a precision instrumen-
tation amplifier. In addition, the MAX9934 is stable into
an infinite capacitive load, allowing filtering flexibility.
Figure 8 shows the MAX9934 in a multiplexed arrange-
ment of strain-gauge amplifiers.
UCSP Applications Information
For the latest application details on UCSP construction,
dimensions, tape carrier information, printed circuit
board techniques, bump-pad layout, and recommend-
ed reflow temperature profile, as well as the latest infor-
mation on reliability testing results go to the Maxim
website at www.maxim-ic.com/ucsp for the
Application Note 1891:
Understanding the Basics of the
Wafer-Level Chip-Scale Package (WL-CSP).
High-Precision, Low-Voltage, Current-Sense Amplifier
with Current Output and Chip Select for Multiplexing
16 ______________________________________________________________________________________
BUCK
CONTROLLER
RS+ RS-
MAX9934
ASIC
Figure 7. One-Sided Input Filter
MAX9934
High-Precision, Low-Voltage, Current-Sense Amplifier
with Current Output and Chip Select for Multiplexing
______________________________________________________________________________________ 17
CS3
CS1
CS2
MICROCONTROLLER
TO EXTERNAL
REFERENCE
VOLTAGE
V
REF
CS
R
R
OUT1
V
OUT
VCC = 3.3V 0.1µF
VIN1
MAX9934
CS
OUT2
VCC = 3.3V 0.1µF
VIN2
CS
OUT3
VCC = 3.3V 0.1µF
VIN3
MAX9934
MAX9934
R
OUT
= R/2
10kΩ(OPTIONAL)
10kΩ
ADC
Figure 8. Multiplexed, Strain-Gauge Amplifier Operation
MAX9934
High-Precision, Low-Voltage, Current-Sense Amplifier
with Current Output and Chip Select for Multiplexing
18 ______________________________________________________________________________________
Chip Information
PROCESS: BiCMOS
RS+
RS-
CS
TOP VIEW
(BUMPS ON BOTTOM)
B2 A2
B3 A3
B1 A1 VCC
OUT
GND
+
UCSP
MAX9934T/F
CS
N.C.
N.C.
1
2
8
7
RS+
RS-OUT
GND
VCC
µMAX
TOP VIEW
3
4
6
5
MAX9934T/F
+
Pin Configurations
MAX9934
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.
UCSP.EPS
PACKAGE TYPE PACKAGE CODE DOCUMENT NO.
2x3 UCSP R61A1+1 21-0228
8 µMAX U8+1 21-0036
High-Precision, Low-Voltage, Current-Sense Amplifier
with Current Output and Chip Select for Multiplexing
______________________________________________________________________________________ 19
MAX9934
High-Precision, Low-Voltage, Current-Sense Amplifier
with Current Output and Chip Select for Multiplexing
20 ______________________________________________________________________________________
α
α
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.
MAX9934
High-Precision, Low-Voltage, Current-Sense Amplifier
with Current Output and Chip Select for Multiplexing
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 ____________________
21
© 2010 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.
Revision History
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
0 10/09 Initial release —
1 1/10 Removed µDFN package option 1–10, 18
2 4/10 Removed future product references and updated lead temperature 1, 2