EVALUATION KIT AVAILABLE
MAX9934
High-Precision, Low-Voltage, Current-Sense Amplifier
with Current Output and Chip Select for Multiplexing
General Description
The MAX9934 high-precision, low-voltage, high-side
current-sense amplifier is ideal for both bidirectional
(charge/discharge) and unidirectional current measurements 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 voltages (typically ±10mV full-scale) for minimally invasive
current sensing.
The output of the MAX9934 is a current proportional to
input V SENSE 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 RSdraw 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
Features
o Input Offset Voltage: 10µV (max)
o Gain Error Less than 0.25%
o -0.1V to +5.5V Input Common-Mode Voltage
Range
o Chip Select Allows Multiplexing Several MAX9934
Current Monitors to One ADC
o Current Output Allows ROUT Selection
for Gain Flexibility
o Single Supply Operation: 2.5V to 3.6V
o Two Gain Options: GM of 25µA/mV (MAX9934T)
and 5µA/mV (MAX9934F)
o Bidirectional or Unidirectional Operation
o Small, 6-Bump UCSP (1mm x 1.5mm x 0.6mm)
and 8-Pin µMAX Packages
Ordering Information
PART
PINPACKAGE
GAIN
MAX9934FART+T
5µA/mV
TOP
MARK
6 UCSP
AAG
MAX9934FAUA+T
5µA/mV
8 µMAX
—
MAX9934FAUA/V+T
5µA/mV
8 µMAX
AAG
MAX9934TART+T
25µA/mV
6 UCSP
AAF
MAX9934TAUA+T
25µA/mV
8 µMAX
—
MAX9934TAUA/V+T
25µA/mV
8 µMAX
AAF
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.
Sensor Instrumentation Amplifiers
Notebook PCs and Ultra-Mobile PCs
Typical Operating Circuit
Portable Current Monitoring
VCC = 3.3V
0.1µF
-0.1V ≤ VCM ≤ 5.5V
ILOAD
VCC
RSENSE
MAX9934
RS-
RS+
µMAX is a registered trademark and UCSP is a trademark of
Maxim Integrated Products, Inc.
VOUT TO ADC
OUT
ROUT
10kΩ
GND
CS
For pricing, delivery, and ordering information, please contact Maxim Direct
at 1-888-629-4642, or visit Maxim’s website at www.maximintegrated.com.
1000pF
FROM µC
CHIP SELECT
19-5011; Rev 3; 11/12
MAX9934
High-Precision, Low-Voltage, Current-Sense Amplifier
with Current Output and Chip Select for Multiplexing
ABSOLUTE MAXIMUM RATINGS
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
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.maximintegrated.com/thermal-tutorial.
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
(VCC = 3.3V, VRS+ = VRS- = 3.0V, VSENSE = 0V, VCM = (VRS+ + VRS-)/2, VCS = 3.3V, ROUT = 10kΩ to GND for unidirectional operation, ROUT = 10kΩ to VCC/2 for bidirectional operation. TA = -40°C to +125°C, unless otherwise noted. Typical values are at TA =
+25°C.) (Note 2)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
DC CHARACTERISTICS
MAX9934T
Input Offset Voltage (Note 3)
VOS
MAX9934F
Input Offset Voltage Drift (Note 3)
VOS/dT
Common-Mode Input Voltage
Range (Average of VRS+ and
VRS-) (Note 3)
CMVR
CMRR1
Common-Mode Rejection Ratio
(Note 3)
CMRR2
2
TA = +25°C
±10
-40°C ≤ TA ≤ +125°C
±14
TA = +25°C
±10
-40°C ≤ TA ≤ +125°C
±20
MAX9934T
±60
MAX9934F
±90
Guaranteed by CMRR2
-0.1
0 ≤ VCM ≤ VCC 0.2V (MAX9934F)
TA = +25°C
128
-40°C ≤ TA ≤ +125°C
112
TA = +25°C
128
-40°C ≤ TA ≤ +125°C
109
0 ≤ VCM ≤ VCC 0.2V (MAX9934T)
-0.1 ≤ VCM ≤ 5.5V
(MAX9934F)
TA = +25°C
119
-40°C ≤ TA ≤ +125°C
104
-0.1 ≤ VCM ≤ 5.5V
(MAX9934T)
TA = +25°C
98
-40°C ≤ TA ≤ +125°C
98
+5.5
µV
nV/°C
V
134
135
125
dB
113
Maxim Integrated
MAX9934
High-Precision, Low-Voltage, Current-Sense Amplifier
with Current Output and Chip Select for Multiplexing
ELECTRICAL CHARACTERISTICS (continued)
(VCC = 3.3V, VRS+ = VRS- = 3.0V, VSENSE = 0V, VCM = (VRS+ + VRS-)/2, VCS = 3.3V, ROUT = 10kΩ to GND for unidirectional operation, ROUT = 10kΩ to VCC/2 for bidirectional operation. TA = -40°C to +125°C, unless otherwise noted. Typical values are at TA =
+25°C.) (Note 2)
PARAMETER
Current Gain (Transconductance)
SYMBOL
GM
CONDITIONS
MAX9934F
5
GME
MAX9934F
Gain Error Drift
Input-Bias Current for RS+
GME/dT
IBRS+
TYP
25
MAX9934T
Current Gain Error
(Note 4)
MIN
MAX9934T
MAX
µA/mV
TA = +25°C
±0.25
-40°C ≤ TA ≤ +125°C
±2.0
TA = +25°C
±0.25
-40°C ≤ TA ≤ +125°C
UNITS
%
±2.4
MAX9934T
±200
MAX9934F
±240
ppm/°C
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
Minimum Current for Output Low
IOL
Unidirectional, VOL = IOL x ROUT
1
100
nA
Output-Voltage Range
(MAX9934T)
VOH
IOUT = +600µA, VOH = VCC - VOUT
0.1
0.25
VOL
IOUT = -600µA, bidirectional
0.15
0.25
Output-Voltage Range
(MAX9934F)
VOH
IOUT = +375µA, VOH = VCC - VOUT
0.18
0.30
VOL
IOUT = -375µA, bidirectional
0.18
0.26
IOLK
VCS = 0V, VOUT = 3.6V,
and 0 ≤ VCC ≤ 3.6V
0.1
100
nA
1.26
V
100
nA
3.6
V
DC CHARACTERISTICS
Deselected Amplifier Output
Leakage
V
V
LOGIC I/O (CS)
Input Voltage Low CS
VIL
Input Voltage High CS
VIH
Input Current CS
0.54
IIL,IIH
0 ≤ VCS ≤ VCC
VCC
Guaranteed by PSRR
2.5
2.5V ≤ VCC ≤ 3.6V,
VRS+ = VRS- = 2V (Note 3)
110
V
0.1
POWER SUPPLY
Supply-Voltage Range
Power-Supply Rejection Ratio
Supply Current
Supply Current, Output
Deselected
PSRR
ICC
ICC,DES
120
dB
VCC = 3.3V, ROUT = 10kΩ to 3.3V,
VRS+ = VRS- = 3.1V
120
230
µA
VCS = 0V, ROUT = 10kΩ to 3.3V,
VRS+ = VRS- = 3.1V
120
210
µA
MAX9934T
GM = 25µA/mV, VSENSE = 5mV
1.5
MAX9934F
GM = 5µA/mV, VSENSE = 25mV
5
AC CHARACTERISTICS (CL = 1000pF)
Amplifier Bandwidth
Maxim Integrated
BW
kHz
3
MAX9934
High-Precision, Low-Voltage, Current-Sense Amplifier
with Current Output and Chip Select for Multiplexing
ELECTRICAL CHARACTERISTICS (continued)
(VCC = 3.3V, VRS+ = VRS- = 3.0V, VSENSE = 0V, VCM = (VRS+ + VRS-)/2, VCS = 3.3V, ROUT = 10kΩ to GND for unidirectional operation, ROUT = 10kΩ to VCC/2 for bidirectional operation. TA = -40°C to +125°C, unless otherwise noted. Typical values are at TA =
+25°C.) (Note 2)
PARAMETER
Output Settling Time
Output Select Time
SYMBOL
tS
tZH
CONDITIONS
MIN
TYP
0.1% final value, Figure 1, MAX9934T
670
0.1% final value, Figure 1, MAX9934F
220
Output to 0.1% final value, Figure 2,
MAX9934T
150
Output to 0.1% final value, Figure 2,
MAX9934F
80
MAX
UNITS
µs
µs
Output Deselect Time
tHZ
Output step of 100mV, CL = 10pF,
Figure 2
2
µs
Power-Down Time
tPD
Output step of -100mV, CL = 10pF,
VCC > 2.5V
2
µs
Power-Up Time
tPU
0.1% final value, Figure 3, MAX9934T
300
0.1% final value, Figure 3, MAX9934F
200
µs
Note 2: All devices are 100% production tested at TA = +25°C. Unless otherwise noted, specifications overtemperature are guaranteed by design.
Note 3: Guaranteed by design. Thermocouple, contact resistance, RS- input-bias current, and leakage effects preclude measurement 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.
4
Maxim Integrated
MAX9934
High-Precision, Low-Voltage, Current-Sense Amplifier
with Current Output and Chip Select for Multiplexing
Typical Operating Characteristics
(VCC = 3.3V, VRS+ = VRS- = 3.0V, VSENSE = 0V, CL = 1000pF, ROUT = 10kΩ to GND for unidirectional operation, ROUT = 10kΩ to
VCC/2 for bidirectional operation. TA = +25°C, unless otherwise noted.)
OFFSET VOLTAGE
vs. COMMON-MODE VOLTAGE
MAX9934T DRIFT VOS HISTOGRAM
35
25
20
N (%)
15
15
10
10
TA = +25NC
TA = -40NC
-4
-2
0
2
4
6
8
10
0
6
-0.1 0.6
12 18 24 30 36 42 48 54 60
1.3
2.0
2.7
3.4
4.1
VOS (FV)
TCVOS (nV/NC)
COMMON-MODE VOLTAGE (V)
OFFSET VOLTAGE
vs. COMMON-MODE VOLTAGE
MAX9934T GAIN ERROR
HISTOGRAM
MAX9934T GAIN ERROR
DRIFT HISTOGRAM
30
VCC = 3.3V
25
VCC = 3.6V
15
15
-2
10
0
0
MAX9934F GAIN ERROR
HISTOGRAM
VOUT vs. VSENSE
VREF = GND
20
30
-200
0.20
0.12
0.16
MAX9934F GAIN ERROR DRIFT
HISTOGRAM
3.5
MAX9934 toc08
35
TC GE (PPM/NC)
25
MAX9934 toc07
40
GE (%)
3.0
MAX9934 toc09
COMMON-MODE VOLTAGE (V)
0.08
5.5
0
4.8
0.04
4.1
-0.04
3.4
-0.08
2.7
-0.12
2.0
-0.16
1.3
-0.20
-10
80
5
120
5
-8
0
10
40
-6
-40
-4
-0.1 0.6
20
-80
0
N (%)
2
N (%)
20
-120
VCC = 2.5V
4
25
MAX9934 toc06
6
5.5
35
MAX9934 toc05
30
MAX9934 toc04
8
4.8
200
-4
160
-6
10
OFFSET VOLTAGE (FV)
0
-2
-10
0
-10 -8
GAIN = 25µA/mV
2.5
20
15
VOUT (V)
N (%)
25
N (%)
2
-8
0
10
15
2.0
GAIN = 5µA/mV
1.5
1.0
10
UNIDIRECTIONAL
5
0.5
Maxim Integrated
TC GE (PPM/°C)
200
160
80
120
40
0
-40
-80
-120
-160
0
-200
0.20
0.16
0.12
0.08
0
GE (%)
0.04
-0.04
-0.08
-0.12
-0.16
-0.20
5
0
4
-6
5
5
TA = +125NC
6
-160
N (%)
20
8
OFFSET VOLTAGE (FV)
30
25
10
MAX9934 toc02
30
MAX9934 toc01
40
MAX9934 toc03
MAX9934T VOS HISTOGRAM
0
0
10
20
30
40
50
60
70
80
VSENSE (mV)
5
MAX9934
High-Precision, Low-Voltage, Current-Sense Amplifier
with Current Output and Chip Select for Multiplexing
Typical Operating Characteristics (continued)
(VCC = 3.3V, VRS+ = VRS- = 3.0V, VSENSE = 0V, CL = 1000pF, ROUT = 10kΩ to GND for unidirectional operation, ROUT = 10kΩ to
VCC/2 for bidirectional operation. TA = +25°C, unless otherwise noted.)
VOUT vs. VSENSE
VREF = 1.65V
VOUT vs. VSENSE (VOUT < 5mV)
BIDIRECTIONAL
1.5
4
1.0
G = 25FA/mV
0.5
VOUT (mV)
VOUT - VREF (V)
MAX9934 toc11
5
MAX9934 toc10
2.0
GAIN = 5µA/mV
0
GAIN = 25µA/mV
-0.5
-1.0
3
G = 5FA/mV
2
1
-1.5
-2.0
0
-20
0
20
40
SUPPLY CURRENT
vs. TEMPERATURE (VCS = 0)
160
MAX9934 toc12
140
SUPPLY CURRENT (µA)
MAX9934F
MAX9934T
100
50
VCM = 0V
120
VCM = 5.5V
100
80
60
0
40
100
200
300
400
500
600
-40 -25 -10 5 20 35 50 65 80 95 110 125
IOH (µA)
TEMPERATURE (°C)
RS+ BIAS CURRENT
vs. VRS+
SUPPLY CURRENT
vs. TEMPERATURE
10nA
MAX9934 toc14
160
VCM = 0V
MAX9934 toc15
0
TA = +125°C
1nA
120
VCM = 5.5V
100
80
RS+ BIAS CURRENT
SUPPLY CURRENT (µA)
100
80
VOH vs. IOH
150
140
60
VSENSE + VOS (FV)
250
200
20
VSENSE (mV)
300
VOH (mV)
0
40
MAX9934 toc13
-40
100pA
TA = +25°C AND -40°C
10pA
60
1pA
40
-40 -25 -10 5 20 35 50 65 80 95 110 125
TEMPERATURE (°C)
6
-0.1 0.6
1.3
2.0
2.7
3.4
4.1
4.8
5.5
VRS+ (V)
Maxim Integrated
MAX9934
High-Precision, Low-Voltage, Current-Sense Amplifier
with Current Output and Chip Select for Multiplexing
Typical Operating Characteristics (continued)
(VCC = 3.3V, VRS+ = VRS- = 3.0V, VSENSE = 0V, CL = 1000pF, ROUT = 10kΩ to GND for unidirectional operation, ROUT = 10kΩ to
VCC/2 for bidirectional operation. TA = +25°C, unless otherwise noted.)
RS- BIAS CURRENT
vs. VRS- (-0.1V ≤ VRS- ≤ VCC)
RS- BIAS CURRENT
vs. VRS- ( 3V ≤ VRS_ ≤ 5.5V)
45
40
RS- BIAS CURRENT (µA)
10nA
1nA
100pA
TA = +25°C AND -40°C
10pA
MAX9934 toc17
TA = +125°C
RS- BIAS CURRENT (pA)
50
MAX9934 toc16
100nA
TA = +125°C
35
TA = +25°C
30
25
TA = -40°C
20
15
10
5
0
1pA
0.4
0.9
1.4
1.9
2.4
2.9
3.0
3.4
3.5
4.0
OUTPUT LEAKAGE CURRENT
vs. VOUT (VCS = 0)
1nA
TA = +125°C
100pA
TA = +25°C
1pA
10nA
OUTPUT LEAKAGE CURRENT
MAX9934 toc18
OUTPUT LEAKAGE CURRENT
5.0
5.5
OUTPUT LEAKAGE CURRENT
vs. VOUT (VCC = 0, VCS = 0)
10nA
10pA
4.5
VRS- (V)
VRS- (V)
MAX9934 toc19
-0.1
TA = +125°C
1nA
100pA
TA = +25°C
TA = -40°C
10pA
TA = -40°C
100fA
1pA
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
VOUT (V)
NORMALIZED GAIN
vs. FREQUENCY
COMMON-MODE REJECTION RATIO
vs. FREQUENCY
10
G = 5FA/mV
0
0
-20
4.0
-40
-10
CMRR (dB)
NORMALIZED GAIN (dB)
0
VOUT (V)
MAX9934 toc21
0.5
MAX9934 toc20
0
G = 25FA/mV
-20
-60
-80
-100
-30
-120
-40
-140
1
10
100
1k
FREQUENCY (Hz)
Maxim Integrated
10k
100k
0.01
0.1
1.0
10
100
FREQUENCY (kHz)
7
MAX9934
High-Precision, Low-Voltage, Current-Sense Amplifier
with Current Output and Chip Select for Multiplexing
Typical Operating Characteristics (continued)
(VCC = 3.3V, VRS+ = VRS- = 3.0V, VSENSE = 0V, CL = 1000pF, ROUT = 10kΩ to GND for unidirectional operation, ROUT = 10kΩ to
VCC/2 for bidirectional operation. TA = +25°C, unless otherwise noted.)
1.0
MAX9934 toc22
0
0.8
-40
PSRR (dB)
±1V VOUT STEP
0.9
SETTING TIME (ms)
-20
MAX9934 toc23
OUTPUT SETTING TIME
vs. PERCENTAGE OF FINAL VALUE
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
-60
-80
0.7
0.6
MAX9934T
0.5
0.4
MAX9934F
0.3
0.2
-100
0.1
0
-120
0.01
0.1
1.0
10
1.00
100
0.10
0.01
PERCENTAGE OF FINAL VALUE (%)
FREQUENCY (kHz)
LARGE-SIGNAL INPUT STEP
RESPONSE (MAX9934F)
LARGE-SIGNAL INPUT STEP
RESPONSE (MAX9934T)
MAX9934 toc24
MAX9934 toc25
VSENSE
20mV/div
VSENSE
5mV/div
0.01% FINAL VALUE
0.01% FINAL VALUE
2V
VOUT
500mV/div
1% FINAL VALUE
1V
2V
VOUT
500mV/div
100µs/div
1V
400µs/div
CS DISABLED TRANSIENT RESPONSE
COUT = 10pF (MAX9934T)
OUTPUT SELECT TIME
MAX9934 toc26
MAX9934 toc27
CL = 0
VCS
2V/div
1% FINAL VALUE
1V
VOUT
500mV/div
1% FINAL VALUE
VCS
2V/div
0.1% FINAL VALUE
MAX9934T
1% FINAL VALUE
1V
VOUT
500mV/div
0.1% FINAL VALUE
MAX9934F
40Fs/div
8
VOUT
1V/div
4µs/div
Maxim Integrated
MAX9934
High-Precision, Low-Voltage, Current-Sense Amplifier
with Current Output and Chip Select for Multiplexing
Typical Operating Characteristics (continued)
(VCC = 3.3V, VRS+ = VRS- = 3.0V, VSENSE = 0V, CL = 1000pF, ROUT = 10kΩ to GND for unidirectional operation, ROUT = 10kΩ to
VCC/2 for bidirectional operation. TA = +25°C, unless otherwise noted.)
SATURATION RECOVERY TIME
VOUT = VOL TO 1V (MAX9934T)
POWER-UP TIME
MAX9934 toc28
MAX9934 toc29
UNIDIRECTIONAL
VCS
2V/div
VSENSE
5mV/div
1% FINAL VALUE
1mV
1V
VOUT
500mV/div
0.1% FINAL VALUE
1% FINAL VALUE
MAX9934T
1V
VOUT
500mV/div
MAX9934F
1V
0.1% FINAL VALUE
VOUT
500mV/div
CBYPASS = 0.1µF
0V
100Fs/div
400Fs/div
SATURATION RECOVERY TIME
VOUT = VOH TO 1V (MAX9934T)
MAX9934 toc30
UNIDIRECTIONAL
VSENSE
10mV/div
VOUT
1V/div
1V
400µs/div
Maxim Integrated
9
MAX9934
High-Precision, Low-Voltage, Current-Sense Amplifier
with Current Output and Chip Select for Multiplexing
Pin Description
PIN/BUMP
NAME
FUNCTION
UCSP
µMAX
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.
Functional Diagram
CS
MAX9934
VSENSE
% FINAL VALUE
VCC
2V
VOUT
±1V STEP
RS+
Gm
Gm
RS-
% FINAL VALUE
*RGAIN
OUT
1V
tS
tS
GND
*RGAIN = 40Ω FOR THE MAX9934T AND
RGAIN = 200Ω FOR THE MAX9934F.
Detailed Description
The MAX9934 high-side, current-sense amplifier monitors 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 resistor (ROUT). See the Typical Operating Circuit.
The MAX9934 uses precision amplifier design techniques 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
10
Figure 1. Output Settling Time
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 loadregulation issues in low-voltage DC power supplies.
The MAX9934 high-side current-sense amplifier features 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
Maxim Integrated
MAX9934
High-Precision, Low-Voltage, Current-Sense Amplifier
with Current Output and Chip Select for Multiplexing
1.8V
3.3V
VCS
VCC
2.5V
0V
0V
% FINAL VALUE
% FINAL VALUE
tHZ
tPD
VOUT
VOUT
100mV
100mV
tZH
Figure 2. Output Select and Deselect Time
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 deselect its output current-source. This allows multiple current-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-feedback architecture. This architecture uses two matched
transconductance amplifiers to convert their input differential 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 transconductance amplifiers feature excellent common-mode rejection characteristics, helping the MAX9934 to deliver
industry-leading precision specifications over the full
common-mode range.
Maxim Integrated
tPU
Figure 3. Output Power-Up and Power-Down Time
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 multiple 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 amplifier 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 current, 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 optimize 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 dissipation) as necessary with fixed-gain, voltage-output
current-sense amplifiers.
11
MAX9934
High-Precision, Low-Voltage, Current-Sense Amplifier
with Current Output and Chip Select for Multiplexing
ILOAD1
VCC = 3.3V
VIN1 -0.1V ≤ VCM ≤ 5.5V
0.1µF
RSENSE
OUT1
MAX9934
MICROCONTROLLER
CS1
ILOAD2
VIN2
-0.1V ≤ VCM ≤ 5.5V
VCC = 3.3V
0.1µF
RSENSE
OUT2
MAX9934
CS2
ILOAD3
VIN3
-0.1V ≤ VCM ≤ 5.5V
VCC = 3.3V
0.1µF
RSENSE
OUT3
MAX9934
CS3
ADC
VOUT
UNIDIRECTIONAL OPERATION
10kΩ
(OPTIONAL)
Figure 4. Typical Application Circuit Showing Chip-Select Multiplexing
Chip-Select Functionality
for Multiplexed Systems
The MAX9934 features a CS that can be used to deselect the output current - source achieving a high-impedance 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 channels are available.
In a multiplexed arrangement, each MAX9934 is typically placed near the load being monitored and all
12
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 reference 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.
Maxim Integrated
MAX9934
High-Precision, Low-Voltage, Current-Sense Amplifier
with Current Output and Chip Select for Multiplexing
ILOAD1
VCC = 3.3V
VIN1 -0.1V ≤ VCM ≤ 5.5V
RSENSE
OUT1
MAX9934
MICROCONTROLLER
CS
CS1
ILOAD2
VCC = 3.3V
VIN2
-0.1V ≤ VCM ≤ 5.5V
RSENSE
OUT2
MAX9934
CS
CS2
ILOAD3
VCC = 3.3V
VIN3
-0.1V ≤ VCM ≤ 5.5V
RSENSE
OUT3
MAX9934
CS3
CS
TO EXTERNAL
REFERENCE
VOLTAGE
R
ROUT = R
2
VOUT
VREF
10kΩ
ADC
R
10kΩ
(OPTIONAL)
Figure 5. Bidirectional Multiplexed Operation
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.
Maxim Integrated
Since the ADC reference voltage, VREF, determines the
full-scale reading, a common choice for V BIAS 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.
13
MAX9934
High-Precision, Low-Voltage, Current-Sense Amplifier
with Current Output and Chip Select for Multiplexing
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 battery life in portable applications.
Choosing RSENSE and ROUT
In the current-sense application, the monitored load
current (I LOAD) develops a sense voltage (V SENSE)
across a current-sense resistor (R SENSE ). The
MAX9934 sources or sinks an output current that is proportional to VSENSE. Finally, the MAX9934 output current is provided to an output resistor (ROUT) to develop
an output voltage across ROUT that is proportional to
the sensed load current.
VCC = 3.3V
ILOAD1
VIN1 -0.1V ≤ VCM ≤ 5.5V
1/4 MAX4737
0.1µF
RSENSE
CS
OUT1
MAX9934
MICROCONTROLLER
CS1
VCC = 3.3V
1/4 MAX4737
ILOAD2
VIN2 -0.1V ≤ VCM ≤ 5.5V
0.1µF
RSENSE
CS
MAX9934
OUT2
CS2
VCC = 3.3V
1/4 MAX4737
ILOAD3
VIN3 -0.1V ≤ VCM ≤ 5.5V
0.1µF
RSENSE
MAX9934
CS
OUT3
CS3
ADC
ROUT
10kΩ
(OPTIONAL)
Figure 6. Multiplexed Amplifiers with Power Saving
14
Maxim Integrated
MAX9934
High-Precision, Low-Voltage, Current-Sense Amplifier
with Current Output and Chip Select for Multiplexing
Three components are to be selected to optimize the
current-sense system: R SENSE , R OUT , and the
MAX9934 gain option (G M = 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 magnitude of I LOAD and the required V SENSE to manage
power dissipation in RSENSE:
RSENSE = VSENSE,MAX/ILOAD,MAX
R SENSE 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 GM x 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 terminal current-sense resistor or Kelvin contacts (force
and sense) PCB layout techniques.
Maxim Integrated
Table 1. Unidirectional Gain Table*
PART
MAX9934T
MAX9934F
VSENSE
(mV)
OUTPUT
CURRENT
(µA)
ROUT
(kΩ)
GAIN
(V/V)
12.4
310
10
250
24.8
620
5
125
62
310
10
50
75
375
8
40
*All calculations were made with VCC = 3.3V and VOUT(MAX) =
VCC - VOH = 3.1V.
Table 2. Bidirectional Gain Table*
OUTPUT
CURRENT
(µA)
ROUT
(kΩ)
±5.8
±145
10
250
±11.6
±290
5
125
±24
±600
2.4
60
±29
±145
10
50
±58
±290
5
25
±72
±360
4
20
PART
VSENSE
(mV)
MAX9934T
MAX9934F
GAIN (V/V)
*All calculations were made with VCC = 3.3V, VOUT(MAX) = VCC VOH = 3.1V, VOUT(MIN) = VOL, and OUT connected to an external reference voltage of VREF = 1.65V through ROUT.
Interfacing the MAX9934 to SAR ADCs
Since the MAX9934 is essentially a high-output impedance 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 specification (10kΩ or 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.
15
MAX9934
High-Precision, Low-Voltage, Current-Sense Amplifier
with Current Output and Chip Select for Multiplexing
Effect of Input-Bias Currents
The MAX9934 has extremely low CMOS input-bias currents at both RS+ and RS- (0.1nA) when the input common-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 operating 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 differential 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
10kΩ can be easily used without impact on error specifications 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 maintain 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 unidirectional mode because the output maintains gain
accuracy below 1mV as shown in the VOUT vs. VSENSE
(VOUT < 5mV) graph in the Typical Operating Char-
16
BUCK
CONTROLLER
ASIC
RS+
RS-
MAX9934
Figure 7. One-Sided Input Filter
acteristics . Extending the useful output below 1mV
makes it possible for the MAX9934 to accurately monitor 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 common-mode rejection, and low V OS of the MAX9934
make it ideally suited for use as a precision instrumentation amplifier. In addition, the MAX9934 is stable into
an infinite capacitive load, allowing filtering flexibility.
Figure 8 shows the MAX9934 in a multiplexed arrangement of strain-gauge amplifiers.
Maxim Integrated
MAX9934
High-Precision, Low-Voltage, Current-Sense Amplifier
with Current Output and Chip Select for Multiplexing
VCC = 3.3V
VIN1
0.1µF
OUT1
MAX9934
CS
CS1
VCC = 3.3V
0.1µF
MICROCONTROLLER
VIN2
OUT2
MAX9934
CS
VCC = 3.3V
VIN3
CS2
0.1µF
OUT3
MAX9934
CS
TO EXTERNAL
REFERENCE
VOLTAGE
R
CS3
VREF
10kΩ
ROUT = R/2
ADC
VOUT
10kΩ
R
(OPTIONAL)
Figure 8. Multiplexed, Strain-Gauge Amplifier Operation
Maxim Integrated
17
MAX9934
High-Precision, Low-Voltage, Current-Sense Amplifier
with Current Output and Chip Select for Multiplexing
Pin Configurations
TOP VIEW
(BUMPS ON BOTTOM)
TOP VIEW
MAX9934T/F
+
+
VCC
1
8
RS+
OUT
2
7
RS-
GND
3
6
CS
N.C. 4
5
N.C.
MAX9934T/F
RS+
B1
A1
VCC
RS-
B2
A2
OUT
CS
B3
A3
GND
µMAX
UCSP
Chip Information
PROCESS: BiCMOS
18
Package Information
For the latest package outline information and land patterns (footprints), go to www.maximintegrated.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
PACKAGE
CODE
OUTLINE NO.
LAND
PATTERN NO.
2x3 UCSP
R61A1+1
21-0228
—
8 µMAX
U8+1
21-0036
90-0092
Maxim Integrated
MAX9934
High-Precision, Low-Voltage, Current-Sense Amplifier
with Current Output and Chip Select for Multiplexing
Revision History
REVISION
NUMBER
REVISION
DATE
0
10/09
Initial release
1
1/10
Removed µDFN package option
2
4/10
Removed future product references and updated lead temperature
3
11/12
Added automotive packages to Ordering Information
DESCRIPTION
PAGES
CHANGED
—
1–10, 18
1, 2
1
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent
licenses are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and
max limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated 160 Rio Robles, San Jose, CA 95134 USA 1-408-601-1000 ________________________________ 19
© 2012 Maxim Integrated Products, Inc.
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.
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