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19-5011; Rev 0; 10/09
KIT ATION EVALU E AILABL AV
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 10V (max) at +25C 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 25A/mV or 5A/mV gain options (GM) with gain accuracy better than 0.25% (max) at +25C. 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 120A (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 -40C to +125C temperature range and is available in 8-pin MAX(R), 6-pin DFN (2mm x 2mm x 0.8mm), or a 6bump UCSPTM (1mm x 1.5mm x 0.6mm), making it ideal for space-sensitive applications. o Input Offset Voltage: 10V (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 25A/mV (MAX9934T) and 5A/mV (MAX9934F) o Bidirectional or Unidirectional Operation o Small, 6-Bump UCSP (1mm x 1.5mm x 0.6mm), 6-Pin DFN (2mm x 2mm x 0.6mm), and 8-Pin MAX Packages
Features
MAX9934
Ordering Information
PART MAX9934FALT+T* MAX9934FART+T* MAX9934FAUA+T MAX9934TALT+T* MAX9934TART+T* MAX9934TAUA+T GAIN 5A/mV 5A/mV 5A/mV 25A/mV 25A/mV 25A/mV PINPACKAGE 6 DFN 6 UCSP 8 MAX 6 DFN 6 UCSP 8 MAX TOP MARK ACP AAG -- ACO AAF --
Applications
PDAs and Smartphones MP3 Players Sensor Instrumentation Amplifiers Notebook PCs and Ultra-Mobile PCs Portable Current Monitoring
Note: All devices are specified over the -40C to +125C extended temperature range.
+Denotes a lead(Pb)-free/RoHS-compliant package.
T = Tape and reel. *Future product--contact factory for availability.
Typical Operating Circuit
VCC = 3.3V 0.1F -0.1V VCM 5.5V ILOAD RSENSE VCC
MAX9934
RSOUT VOUT TO ADC
RS+
ROUT 10k GND CS FROM C CHIP SELECT
1000pF
MAX is a registered trademark and UCSP is a trademark of Maxim Integrated Products, Inc. **Patent pending.
________________________________________________________________ Maxim Integrated Products
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For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
High-Precision, Low-Voltage, Current-Sense Amplifier with Current Output and Chip Select for Multiplexing MAX9934
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 = +70C) 8-Pin MAX (derate multilayer 4.8mW/C above +70C).............................................................388mW Junction-to-Ambient Thermal Resistance (JA) (Note 1) ....................................................................206C/W Junction-to-Case Thermal Resistance (JC) (Note 1) ......................................................................42C/W 6-Pin DFN (derate multilayer 4.5mW/C above +70C)..........................................................357.8mW Junction-to-Ambient Thermal Resistance (JA) (Note 1 ) ................................................................223.6C/W Junction-to-Case Thermal Resistance (JA) (Note 1) ....................................................................122C/W 6-Bump UCSP (derate multilayer 3.9mW/C above +70C).............................................................308mW Junction-to-Ambient Thermal Resistance (JA) (Note 1) ....................................................................260C/W Operating Temperature Range .........................-40C to +125C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +160C Lead Temperature (soldering, 10s) .................................+300C Reflow Soldering Temperature (UCSP, DFN, and MAX) ..........................................................................+260C
Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a fourlayer board. For detailed information on package thermal considerations, refer to www.maxim-ic.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 = 0, VCM = (VRS+ + VRS-)/2, VCS = 3.3V, ROUT = 10k to GND for unidirectional operation, ROUT = 10k to VCC/2 for bidirectional operation. TA = -40C to +125C, unless otherwise noted. Typical values are at TA = +25C.) (Note 2)
PARAMETER DC CHARACTERISTICS MAX9934T Input Offset Voltage (Note 3) VOS MAX9934F Input Offset Voltage Drift (Note 3) Common-Mode Input Voltage Range (Average of VRS+ and VRS-) (Note 3) VOS/dT MAX9934T MAX9934F Guaranteed by CMRR2 0 VCM VCC 0.2V (MAX9934F) CMRR1 Common-Mode Rejection Ratio (Note 3) CMRR2 0 VCM VCC 0.2V (MAX9934T) -0.1 VCM 5.5V (MAX9934F) -0.1 VCM 5.5V (MAX9934T) TA = +25C -40C TA +125C TA = +25C -40C TA +125C TA = +25C -40C TA +125C TA = +25C -40C TA +125C -0.1 128 112 128 109 119 104 98 98 113 125 135 dB 134 TA = +25C -40C TA +125C TA = +25C -40C TA +125C 10 14 10 20 60 90 +5.5 nV/C V SYMBOL CONDITIONS MIN TYP MAX UNITS
CMVR
V
2
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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 = 0, VCM = (VRS+ + VRS-)/2, VCS = 3.3V, ROUT = 10k to GND for unidirectional operation, ROUT = 10k to VCC/2 for bidirectional operation. TA = -40C to +125C, unless otherwise noted. Typical values are at TA = +25C.) (Note 2)
PARAMETER Current Gain (Transconductance) SYMBOL GM MAX9934T MAX9934F MAX9934T Current Gain Error (Note 4) GME MAX9934F Gain Error Drift Input-Bias Current for RS+ Input-Bias Current for RSInput Leakage Current DC CHARACTERISTICS Minimum Current for Output Low Output-Voltage Range (MAX9934T) Output-Voltage Range (MAX9934F) Deselected Amplifier Output Leakage LOGIC I/O (CS) Input Voltage Low CS Input Voltage High CS Input Current CS POWER SUPPLY Supply-Voltage Range Power-Supply Rejection Ratio Supply Current Supply Current, Output Deselected VCC PSRR ICC ICC,DES Guaranteed by PSRR 2.5V VCC 3.6V, VRS+ = VRS- = 2V (Note 3) VCC = 3.3V, ROUT = 10k to 3.3V, VRS+ = VRS- = 3.1V VCS = 0, ROUT = 10k to 3.3V, VRS+ = VRS- = 3.1V MAX9934T GM = 25A/mV, VSENSE = 5mV MAX9934F GM = 5A/mV, VSENSE = 25mV 2.5 110 120 120 120 230 210 3.6 V dB A A VIL VIH IIL,IIH 0 VCS VCC 0.1 0.54 1.26 100 V V nA IOL VOH VOL VOH VOL IOLK Unidirectional, VOL = IOL x ROUT IOUT = +600A, VOH = VCC - VOUT IOUT = -600A, bidirectional IOUT = +375A, VOH = VCC - VOUT IOUT = -375A, bidirectional VCS = 0, VOUT = 3.6V, and 0 VCC 3.6V 1 0.1 0.15 0.18 0.18 0.1 100 0.25 0.25 0.30 0.26 100 nA V V nA GME/dT IBRS+ IBRSILEK MAX9934T MAX9934F VRS+ = VRS- = 5.5V VRS+ = VRS- VCC - 0.2V VRS+ = VRS- = 5.5V VCC = 0, VRS+ = VRS- = 5.5V 0.1 0.1 35 0.1 TA = +25C -40C TA +125C TA = +25C -40C TA +125C CONDITIONS MIN TYP 25 5 0.25 2.0 0.25 2.4 200 240 100 100 60 100 ppm/C nA nA A nA % MAX UNITS A/mV
MAX9934
AC CHARACTERISTICS (CL = 1000pF) 1.5 kHz 5
Amplifier Bandwidth
BW
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High-Precision, Low-Voltage, Current-Sense Amplifier with Current Output and Chip Select for Multiplexing MAX9934
ELECTRICAL CHARACTERISTICS (continued)
(VCC = 3.3V, VRS+ = VRS- = 3.0V, VSENSE = 0, VCM = (VRS+ + VRS-)/2, VCS = 3.3V, ROUT = 10k to GND for unidirectional operation, ROUT = 10k to VCC/2 for bidirectional operation. TA = -40C to +125C, unless otherwise noted. Typical values are at TA = +25C.) (Note 2)
PARAMETER Output Settling Time SYMBOL tS CONDITIONS 0.1% final value, Figure 1, MAX9934T 0.1% final value, Figure 1, MAX9934F Output to 0.1% final value, Figure 2, MAX9934T Output Select Time tZH Output to 0.1% final value, Figure 2, MAX9934F Output step of 100mV, CL = 10pF, Figure 2 Output step of -100mV, CL = 10pF, VCC > 2.5V 0.1% final value, Figure 3, MAX9934T 0.1% final value, Figure 3, MAX9934F MIN TYP 670 220 150 s 80 2 2 300 200 s s s MAX UNITS s
Output Deselect Time Power-Down Time Power-Up Time
tHZ tPD tPU
Note 2: All devices are 100% production tested at TA = +25C. 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.
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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 = 0, CL = 1000pF, ROUT = 10k to GND for unidirectional operation, ROUT = 10k to VCC/2 for bidirectional operation. TA = +25C, unless otherwise noted.)
OFFSET VOLTAGE vs. COMMON-MODE VOLTAGE
MAX9934 toc02
MAX9934
MAX9934T VOS HISTOGRAM
MAX9934 toc01
MAX9934T DRIFT VOS HISTOGRAM
30 25 20 N (%) 15 10 5 0 10 8 6 OFFSET VOLTAGE (FV) 4 2 0 -2 -4 -6 -8 -10 0 6 12 18 24 30 36 42 48 54 60 TCVOS (nV/NC)
35 30 25 N (%) 20 15 10 5 0 -10 -8 -6 -4 -2 0 2 4 6 8
TA = +125NC
TA = +25NC TA = -40NC
10
-0.1 0.6
1.3
2.0
2.7
3.4
4.1
4.8
5.5
VOS (FV)
COMMON-MODE VOLTAGE (V)
OFFSET VOLTAGE vs. COMMON-MODE VOLTAGE
8 6 OFFSET VOLTAGE (FV) 4 2 0 -2 -4 -6 -8 -10 -0.1 0.6 1.3 2.0 2.7 3.4 4.1 4.8 5.5 COMMON-MODE VOLTAGE (V) 0
-0.20
MAX9934 toc04
MAX9934T GAIN ERROR HISTOGRAM
MAX9934 toc05
MAX9934T GAIN ERROR DRIFT HISTOGRAM
MAX9934 toc06
10
30 25 20 N (%)
35 30 25 N (%) 20 15
VCC = 2.5V
VCC = 3.3V
VCC = 3.6V
15 10 5
10 5 0
0.12 -0.16 -0.12 -0.08 -0.04 0.04 0.08 0.16 0.20 0
-200
-160
-120
-80
-40
0
40
80
120
160
GE (%)
TC GE (PPM/NC)
MAX9934F GAIN ERROR HISTOGRAM
MAX9934 toc07
MAX9934F GAIN ERROR DRIFT HISTOGRAM
MAX9934 toc08
VOUT vs. VSENSE VREF = GND
MAX9934 toc09
40 35 30 25 N (%)
25
3.5 3.0 2.5 VOUT (V) GAIN = 25A/mV
20
N (%)
15
2.0 1.5 1.0
20 15 10 5
-0.12 -0.08 0.04 0.08 0.12 0.16 -0.20 -0.16 -0.04 0.20 0
GAIN = 5A/mV
10
5 0.5 0 -120 -200 -160 -80 -40 0 40 80 120 160 200 TC GE (PPM/C) 0 0 10 20
UNIDIRECTIONAL
0
30
40
50
60
70
GE (%)
VSENSE (mV)
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200
80
5
MAX9934 toc03
40
High-Precision, Low-Voltage, Current-Sense Amplifier with Current Output and Chip Select for Multiplexing MAX9934
Typical Operating Characteristics (continued)
(VCC = 3.3V, VRS+ = VRS- = 3.0V, VSENSE = 0, CL = 1000pF, ROUT = 10k to GND for unidirectional operation, ROUT = 10k to VCC/2 for bidirectional operation. TA = +25C, unless otherwise noted.)
VOUT vs. VSENSE VREF = 1.65V
MAX9934 toc10
VOUT vs. VSENSE (VOUT < 5mV)
MAX9934 toc11
2.0 BIDIRECTIONAL 1.5 1.0 VOUT - VREF (V)
5
4 G = 25FA/mV
0 -0.5 -1.0 -1.5 -2.0 -40
GAIN = 5A/mV GAIN = 25A/mV
VOUT (mV)
0.5
3 G = 5FA/mV 2
1
0 -20 0 VSENSE (mV) 20 40 0 20 40 60 80 100 VSENSE + VOS (FV)
VOH vs. IOH
MAX9934 toc12
SUPPLY CURRENT vs. TEMPERATURE (VCS = 0)
MAX9934 toc13
300 250 200 VOH (mV) 150 100 50 0 0 100 200 300 IOH (A) 400 500 MAX9934T MAX9934F
160 140 SUPPLY CURRENT (A) 120 100 80 60 40 VCM = 5.5V
VCM = 0V
600
-40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C)
SUPPLY CURRENT vs. TEMPERATURE
MAX9934 toc14
RS+ BIAS CURRENT vs. VRS+
MAX9934 toc15
160 140 SUPPLY CURRENT (A) 120 VCM = 5.5V 100 80 60 40 VCM = 0V
10nA TA = +125C 1nA RS+ BIAS CURRENT
100pA TA = +25C AND -40C 10pA
1pA -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C) -0.1 0.6 1.3 2.0 2.7 VRS+ (V) 3.4 4.1 4.8 5.5
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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 = 0, CL = 1000pF, ROUT = 10k to GND for unidirectional operation, ROUT = 10k to VCC/2 for bidirectional operation. TA = +25C, unless otherwise noted.)
RS- BIAS CURRENT vs. VRS- (-0.1V VRS- VCC)
TA = +125C 10nA RS- BIAS CURRENT (pA)
MAX9934 toc16
MAX9934
RS- BIAS CURRENT vs. VRS- ( 3V VRS_ 5.5V)
45 40 RS- BIAS CURRENT (A) 35 30 25 20 15 10 5 TA = -40C TA = +25C TA = +125C
MAX9934 toc17
100nA
50
1nA
100pA TA = +25C AND -40C
10pA
1pA -0.1 0.4 0.9 1.4 1.9 2.4 2.9 3.4 VRS- (V)
0 3.0 3.5 4.0 4.5 5.0 5.5 VRS- (V)
OUTPUT LEAKAGE CURRENT vs. VOUT (VCS = 0)
MAX9934 toc18
OUTPUT LEAKAGE CURRENT vs. VOUT (VCC = 0, VCS = 0)
MAX9934 toc19
10nA
10nA
OUTPUT LEAKAGE CURRENT
OUTPUT LEAKAGE CURRENT
1nA TA = +125C 100pA TA = +25C
1nA
TA = +125C
100pA TA = +25C 10pA
10pA
TA = -40C
1pA TA = -40C 100fA 0 0.5 1.0 1.5 2.0 VOUT (V) 2.5 3.0 3.5 4.0
1pA 0 0.5 1.0 1.5 2.0 VOUT (V) 2.5 3.0 3.5 4.0
NORMALIZED GAIN vs. FREQUENCY
MAX9934 toc20
COMMON-MODE REJECTION RATIO vs. FREQUENCY
MAX9934 toc21
10 G = 5FA/mV 0 NORMALIZED GAIN (dB)
0 -20 -40
-10
G = 25FA/mV
CMRR (dB) 10k 100k
-60 -80 -100
-20
-30 -120 -40 1 10 100 1k FREQUENCY (Hz) -140 0.01 0.1 1.0 FREQUENCY (kHz) 10 100
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High-Precision, Low-Voltage, Current-Sense Amplifier with Current Output and Chip Select for Multiplexing MAX9934
Typical Operating Characteristics (continued)
(VCC = 3.3V, VRS+ = VRS- = 3.0V, VSENSE = 0, CL = 1000pF, ROUT = 10k to GND for unidirectional operation, ROUT = 10k to VCC/2 for bidirectional operation. TA = +25C, unless otherwise noted.)
POWER-SUPPLY REJECTION RATIO vs. FREQUENCY
MAX9934 toc22
OUTPUT SETTING TIME vs. PERCENTAGE OF FINAL VALUE
0.9 0.8 SETTING TIME (ms) 0.7 0.6 0.5 0.4 0.3 0.2 0.1 MAX9934F MAX9934T 1V VOUT STEP
MAX9934 toc23
0 -20 -40 PSRR (dB) -60 -80 -100 -120 0.01 0.1 1.0 FREQUENCY (kHz) 10
1.0
0 100 1.00 0.10 PERCENTAGE OF FINAL VALUE (%) 0.01
LARGE-SIGNAL INPUT STEP RESPONSE (MAX9934F)
MAX9934 toc24
LARGE-SIGNAL INPUT STEP RESPONSE (MAX9934T)
MAX9934 toc25
VSENSE 20mV/div 0.01% FINAL VALUE 2V
VSENSE 5mV/div 0.01% FINAL VALUE 2V
VOUT 500mV/div
1% FINAL VALUE 1V
VOUT 500mV/div
1% FINAL VALUE
1V
100s/div
400s/div
OUTPUT SELECT TIME
MAX9934 toc26
CS DISABLED TRANSIENT RESPONSE COUT = 10pF (MAX9934T)
CL = 0 VCS 2V/div
MAX9934 toc27
VCS 2V/div VOUT 500mV/div
1% FINAL VALUE 1V 0.1% FINAL VALUE MAX9934T 1% FINAL VALUE 1V
VOUT 500mV/div MAX9934F
0.1% FINAL VALUE
VOUT 1V/div
40Fs/div
4s/div
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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 = 0, CL = 1000pF, ROUT = 10k to GND for unidirectional operation, ROUT = 10k to VCC/2 for bidirectional operation. TA = +25C, unless otherwise noted.)
MAX9934
POWER-UP TIME
MAX9934 toc28
SATURATION RECOVERY TIME VOUT = VOL TO 1V (MAX9934T)
MAX9934 toc29
VCS 2V/div 1% FINAL VALUE 1V VOUT 500mV/div VOUT 500mV/div 0.1% FINAL VALUE MAX9934T 1% FINAL VALUE 1V 0.1% FINAL VALUE CBYPASS = 0.1F 100Fs/div
UNIDIRECTIONAL VSENSE 5mV/div
1mV
1V
MAX9934F
VOUT 500mV/div 400Fs/div
0V
SATURATION RECOVERY TIME VOUT = VOH TO 1V (MAX9934T)
MAX9934 toc30
UNIDIRECTIONAL VSENSE 10mV/div
VOUT 1V/div 1V
400s/div
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High-Precision, Low-Voltage, Current-Sense Amplifier with Current Output and Chip Select for Multiplexing MAX9934
Pin Description
PIN/BUMP UCSP A1 A2 A3 B1 B2 B3 -- MAX 1 2 3 8 7 6 4, 5 DFN 1 2 3 6 5 4 -- NAME VCC OUT GND RS+ RSCS N.C. Power Supply 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. Ground Sense Resistor Power Side Connection Sense Resistor Load Side Connection Chip-Select Input. Drive CS high to enable OUT, drive CS low to put OUT in a highimpedance state. No Connection. Not internally connected. FUNCTION
Functional Diagram
CS
VSENSE % FINAL VALUE
MAX9934
VCC
2V
RS+ Gm RSGm *RGAIN OUT
VOUT 1V STEP
% FINAL VALUE
1V tS tS
GND *RGAIN = 40 FOR THE MAX9934T AND RGAIN = 200 FOR THE MAX9934F.
Figure 1. Output Settling Time
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 10V. These techniques also enable extremely low-input offset voltage drift over time and temperature and
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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
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High-Precision, Low-Voltage, Current-Sense Amplifier with Current Output and Chip Select for Multiplexing MAX9934
1.8V
3.3V
VCS
VCC 2.5V
0V
% FINAL VALUE tHZ
0V
% FINAL VALUE tPD
VOUT 100mV
VOUT 100mV
tZH
tPU
Figure 2. Output Select and Deselect Time
Figure 3. Output Power-Up and Power-Down 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.
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.
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High-Precision, Low-Voltage, Current-Sense Amplifier with Current Output and Chip Select for Multiplexing MAX9934
ILOAD1 VCC = 3.3V VIN1 -0.1V VCM 5.5V RSENSE 0.1F
OUT1
MAX9934
MICROCONTROLLER CS1
ILOAD2 VIN2 -0.1V VCM 5.5V VCC = 3.3V 0.1F RSENSE
OUT2
MAX9934
CS2 ILOAD3 VIN3 -0.1V VCM 5.5V VCC = 3.3V 0.1F RSENSE OUT3
MAX9934
CS3 ADC
VOUT UNIDIRECTIONAL OPERATION 10k (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
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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.
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High-Precision, Low-Voltage, Current-Sense Amplifier with Current Output and Chip Select for Multiplexing MAX9934
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 ILOAD3 VCC = 3.3V VIN3 -0.1V VCM 5.5V RSENSE OUT3
MAX9934
CS2
CS TO EXTERNAL REFERENCE VOLTAGE R ROUT = R 2 VOUT 10k R 10k
CS3
VREF ADC
(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.
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.
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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 = 0 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 = 0) reduces its supply current to zero to help extend battery life in portable applications.
MAX9934
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 0.1F
RSENSE CS OUT1
MAX9934
MICROCONTROLLER CS1
VCC = 3.3V ILOAD2 VIN2 -0.1V VCM 5.5V
1/4 MAX4737 0.1F
RSENSE CS OUT2
MAX9934
CS2 VCC = 3.3V ILOAD3 VIN3 -0.1V VCM 5.5V 1/4 MAX4737 0.1F RSENSE CS OUT3
MAX9934
CS3
ADC ROUT 10k (OPTIONAL)
Figure 6. Multiplexed Amplifiers with Power Saving
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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 = 25A/mV or 5A/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
MAX9934
Table 1. Unidirectional Gain Table*
PART VSENSE (mV) 12.4 24.8 62 75 OUTPUT CURRENT (A) 310 620 310 375 ROUT (k) 10 5 10 8 GAIN (V/V) 250 125 50 40
MAX9934T MAX9934F
*All calculations were made with VCC = 3.3V and VOUT(MAX) = VCC - VOH = 3.1V.
Table 2. Bidirectional Gain Table*
PART VSENSE (mV) 5.8 MAX9934T 11.6 24 29 MAX9934F 58 72 OUTPUT CURRENT (A) 145 290 600 145 290 360 ROUT (k) 10 5 2.4 10 5 4 GAIN (V/V)
250 125 60 50 25 20
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 10V 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.
*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 (10k 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.
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.
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15
High-Precision, Low-Voltage, Current-Sense Amplifier with Current Output and Chip Select for Multiplexing MAX9934
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-, 35A (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 10k 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.
BUCK CONTROLLER
ASIC
RS+
RS-
MAX9934
Figure 7. One-Sided Input Filter
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.
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 35A 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 Characteristics. Extending the useful output below 1mV makes it possible for the MAX9934 to accurately monitor very low currents.
UCSP Applications Information
For the latest application details on UCSP construction, dimensions, tape carrier information, printed circuit board techniques, bump-pad layout, and recommended reflow temperature profile, as well as the latest information 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).
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High-Precision, Low-Voltage, Current-Sense Amplifier with Current Output and Chip Select for Multiplexing MAX9934
VCC = 3.3V 0.1F
VIN1
OUT1
MAX9934
CS CS1 VCC = 3.3V
0.1F MICROCONTROLLER
VIN2
OUT2
MAX9934
CS
CS2
VCC = 3.3V
0.1F
VIN3
OUT3
MAX9934
CS TO EXTERNAL REFERENCE VOLTAGE R 10k VOUT
CS3
VREF ROUT = R/2 ADC
10k
R (OPTIONAL)
Figure 8. Multiplexed, Strain-Gauge Amplifier Operation
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17
High-Precision, Low-Voltage, Current-Sense Amplifier with Current Output and Chip Select for Multiplexing MAX9934
Pin Configurations
TOP VIEW +
VCC OUT GND 1 2 8 7 RS+ RSCS N.C. CS B3 A3 GND RSB2 A2 OUT OUT 2 RS+ B1 A1 TOP VIEW (BUMPS ON BOTTOM)
MAX9934T/F
+ VCC VCC + 1 6 RS+
MAX9934T/F
3 6 5 N.C. 4
MAX9934T/F
5
RS-
GND
3
4
CS
MAX UCSP DFN
Chip Information
PROCESS: BiCMOS
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High-Precision, Low-Voltage, Current-Sense Amplifier with Current Output and Chip Select for Multiplexing
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. PACKAGE TYPE 2x3 UCSP 6 DFN 8 MAX PACKAGE CODE R61A1+1 L622+1 U8+1 DOCUMENT NO. 21-0228 21-0164 21-0036
UCSP.EPS
MAX9934
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High-Precision, Low-Voltage, Current-Sense Amplifier with Current Output and Chip Select for Multiplexing MAX9934
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.
6, 8, 10L UDFN.EPS
1 2
D
A
e
b
N
AAA AAA
E
SOLDER MASK COVERAGE
PIN 1 0.10x45
L
PIN 1 INDEX AREA SAMPLE MARKING 1 A A
L1
7
(N/2 -1) x e)
C L
C L
b A A2 A1
L e
EVEN TERMINAL
L e
ODD TERMINAL
PACKAGE OUTLINE, 6, 8, 10L uDFN, 2x2x0.80 mm
21-0164
B
20
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High-Precision, Low-Voltage, Current-Sense Amplifier with Current Output and Chip Select for Multiplexing
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
COMMON DIMENSIONS SYMBOL A A1 A2 D E L L1 MIN. 0.70 0.15 0.020 1.95 1.95 0.30 NOM. 0.75 0.20 0.025 2.00 2.00 0.40 0.10 REF. MAX. 0.80 0.25 0.035 2.05 2.05 0.50
PACKAGE VARIATIONS PKG. CODE L622-1 L822-1 L1022-1 N 6 8 10 e 0.65 BSC 0.50 BSC 0.40 BSC b 0.300.05 0.250.05 0.200.03 (N/2 -1) x e 1.30 REF. 1.50 REF. 1.60 REF.
PACKAGE OUTLINE, 6, 8, 10L uDFN, 2x2x0.80 mm
21-0164
B
2
2
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High-Precision, Low-Voltage, Current-Sense Amplifier with Current Output and Chip Select for Multiplexing MAX9934
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.
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.
22 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2009 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.

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