MAX9934FART+T - Maxim Integrated

MAX9934

High-Precision, Low-Voltage, Current-Sense Amplifier

with Current Output and Chip Select for Multiplexing

EVALUATION KIT AVAILABLE

19-5011; Rev 3; 11/12

For pricing, delivery, and ordering information, please contact Maxim Direct

at 1-888-629-4642, or visit Maxim’s website at www.maximintegrated.com.

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

oInput Offset Voltage: 10µV (max)

oGain Error Less than 0.25%

o-0.1V to +5.5V Input Common-Mode Voltage

Range

oChip Select Allows Multiplexing Several MAX9934

Current Monitors to One ADC

oCurrent Output Allows ROUT Selection

for Gain Flexibility

oSingle Supply Operation: 2.5V to 3.6V

oTwo Gain Options: GMof 25µA/mV (MAX9934T)

and 5µA/mV (MAX9934F)

oBidirectional or Unidirectional Operation

oSmall, 6-Bump UCSP (1mm x 1.5mm x 0.6mm)

and 8-Pin µMAX Packages

Ordering Information

PART GAIN PIN-

PACKAGE

TOP

MARK

MAX9934FART+T 5µA/mV 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.

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

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

2Maxim Integrated

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

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.

MAX9934

High-Precision, Low-Voltage, Current-Sense Amplifier

with Current Output and Chip Select for Multiplexing

Maxim Integrated

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

4Maxim Integrated

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

Maxim Integrated

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

-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

-10

-0.1 5.5

VCC = 3.3V

VCC = 3.6V

VCC = 2.5V

MAX9934T DRIFT VOS HISTOGRAM

MAX9934 toc02

TCVOS (nV/NC)

N (%)

6 1218243036424854

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

-10

-0.1 5.5

TA = +125NC

TA = +25NC

TA = -40NC

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

-0.16

-0.12

-0.08

-0.04

0.04

0.08

0.12

0.16

-0.20

0.20

MAX9934T GAIN ERROR

HISTOGRAM

MAX9934 toc05

GE (%)

N (%)

-160

-120

-80

-40

120

160

-200

200

MAX9934T GAIN ERROR

DRIFT HISTOGRAM

MAX9934 toc06

TC GE (PPM/NC)

N (%)

-0.16

-0.12

-0.08

-0.04

0.04

0.08

0.12

0.16

-0.20

0.20

MAX9934F GAIN ERROR

HISTOGRAM

MAX9934 toc07

GE (%)

N (%)

-160

-120

-80

-40

120

160

-200

200

MAX9934F GAIN ERROR DRIFT

HISTOGRAM

MAX9934 toc08

TC GE (PPM/°C)

N (%)

MAX9934

High-Precision, Low-Voltage, Current-Sense Amplifier

with Current Output and Chip Select for Multiplexing

6Maxim Integrated

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

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

0100

G = 25FA/mV

G = 5FA/mV

100

200

150

250

300

0 200 300100 400 500 600

VOH vs. IOH

MAX9934 toc12

IOH (µA)

VOH (mV)

MAX9934F

MAX9934T

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

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

1pA

10pA

100pA

1nA

10nA

-0.1 1.3 2.7 4.10.6 2.0 3.4 4.8 5.5

RS+ BIAS CURRENT

vs. VRS+

MAX9934 toc15

VRS+ (V)

RS+ BIAS CURRENT

TA = +125°C

TA = +25°C AND -40°C

MAX9934

High-Precision, Low-Voltage, Current-Sense Amplifier

with Current Output and Chip Select for Multiplexing

Maxim Integrated

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.)

1pA

10pA

1nA

100pA

10nA

100nA

-0.1 0.90.4 1.4 1.9 2.4 2.9 3.4

RS- BIAS CURRENT

vs. VRS- (-0.1V ≤ VRS- ≤ VCC)

MAX9934 toc16

VRS- (V)

RS- BIAS CURRENT (pA)

TA = +125°C

TA = +25°C AND -40°C

3.0 4.03.5 4.5 5.0 5.5

RS- BIAS CURRENT

vs. VRS- ( 3V ≤ VRS_ ≤ 5.5V)

MAX9934 toc17

VRS- (V)

RS- BIAS CURRENT (µA)

TA = +125°C

TA = +25°C

TA = -40°C

100fA

1pA

100pA

10pA

1nA

10nA

0 1.0 1.50.5 2.0 2.5 3.0 3.5 4.0

OUTPUT LEAKAGE CURRENT

vs. VOUT (VCS = 0)

MAX9934 toc18

VOUT (V)

OUTPUT LEAKAGE CURRENT

TA = +125°C

TA = +25°C

TA = -40°C

1pA

10pA

100pA

1nA

10nA

0 1.0 2.0 3.00.5 1.5 2.5 3.5 4.0

OUTPUT LEAKAGE CURRENT

vs. VOUT (VCC = 0, VCS = 0)

MAX9934 toc19

VOUT (V)

OUTPUT LEAKAGE CURRENT

TA = +125°C

TA = +25°CTA = -40°C

NORMALIZED GAIN

vs. FREQUENCY

MAX9934 toc20

FREQUENCY (Hz)

NORMALIZED GAIN (dB)

10k1k10010

-30

-20

-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

-140

0.01 100

MAX9934

High-Precision, Low-Voltage, Current-Sense Amplifier

with Current Output and Chip Select for Multiplexing

8Maxim Integrated

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

-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

1.00 0.01

±1V VOUT STEP

MAX9934T

MAX9934F

100µs/div

LARGE-SIGNAL INPUT STEP

RESPONSE (MAX9934F)

VSENSE

20mV/div

VOUT

500mV/div

MAX9934 toc24

0.01% FINAL VALUE

1% FINAL VALUE

400µs/div

LARGE-SIGNAL INPUT STEP

RESPONSE (MAX9934T)

VSENSE

5mV/div

VOUT

500mV/div

MAX9934 toc25

0.01% FINAL VALUE

1% FINAL VALUE

MAX9934 toc26

40Fs/div

VCS

2V/div

VOUT

500mV/div

VOUT

500mV/div

1% FINAL VALUE

0.1% FINAL VALUE

MAX9934T

MAX9934F

1% FINAL VALUE

OUTPUT SELECT TIME

4µs/div

CS DISABLED TRANSIENT RESPONSE

COUT = 10pF (MAX9934T)

VCS

2V/div

VOUT

1V/div

MAX9934 toc27

CL = 0

MAX9934

High-Precision, Low-Voltage, Current-Sense Amplifier

with Current Output and Chip Select for Multiplexing

Maxim Integrated

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

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

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

UNIDIRECTIONAL

MAX9934

High-Precision, Low-Voltage, Current-Sense Amplifier

with Current Output and Chip Select for Multiplexing

10 Maxim Integrated

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

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

OUT

±1V STEP

% FINAL VALUE

SENSE

Figure 1. Output Settling Time

OUT

GND

RS-

RS+

VCC

*RGAIN

MAX9934

*RGAIN = 40Ω FOR THE MAX9934T AND

RGAIN = 200Ω FOR THE MAX9934F.

Functional Diagram

MAX9934

High-Precision, Low-Voltage, Current-Sense Amplifier

with Current Output and Chip Select for Multiplexing

Maxim Integrated

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.

100mV

tHZ

% FINAL VALUE

tZH

VOUT

1.8V

VCS

Figure 2. Output Select and Deselect Time

100mV

tPD

% FINAL VALUE

tPU

VCC

VOUT

3.3V

2.5V

Figure 3. Output Power-Up and Power-Down Time

MAX9934

High-Precision, Low-Voltage, Current-Sense Amplifier

with Current Output and Chip Select for Multiplexing

12 Maxim Integrated

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.

VCC = 3.3V

RSENSE

-0.1V ≤ VCM ≤ 5.5V

RSENSE

-0.1V ≤ VCM ≤ 5.5V

RSENSE

-0.1V ≤ VCM ≤ 5.5V

MAX9934

10kΩ

(OPTIONAL)

ADC

CS3

CS2

CS1

MICROCONTROLLER

VIN1

VIN2

VIN3

ILOAD3

ILOAD2

ILOAD1

VOUT

0.1µF

OUT3

OUT2

OUT1

UNIDIRECTIONAL OPERATION

Figure 4. Typical Application Circuit Showing Chip-Select Multiplexing

MAX9934

High-Precision, Low-Voltage, Current-Sense Amplifier

with Current Output and Chip Select for Multiplexing

Maxim Integrated

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.

VCC = 3.3V

RSENSE

-0.1V ≤ VCM ≤ 5.5V

RSENSE

-0.1V ≤ VCM ≤ 5.5V

RSENSE

-0.1V ≤ VCM ≤ 5.5V

MAX9934

10kΩ

ADC

VREF

CS2

CS1

MICROCONTROLLER

TO EXTERNAL

REFERENCE

VOLTAGE

10kΩ

CS3

(OPTIONAL)

VIN1

VIN2

VIN3

ILOAD3

ILOAD2

ILOAD1

VOUT

OUT3

OUT2

OUT1

ROUT = R

Figure 5. Bidirectional Multiplexed Operation

MAX9934

High-Precision, Low-Voltage, Current-Sense Amplifier

with Current Output and Chip Select for Multiplexing

14 Maxim Integrated

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.

VCC = 3.3V

RSENSE

-0.1V ≤ VCM ≤ 5.5V

MAX9934

ROUT

10kΩ

(OPTIONAL)

ADC

CS2

CS1

MICROCONTROLLER

CS3

VCC = 3.3V

RSENSE

-0.1V ≤ VCM ≤ 5.5V

MAX9934

VCC = 3.3V

RSENSE

-0.1V ≤ VCM ≤ 5.5V

MAX9934

1/4 MAX4737

VIN1

VIN2

VIN3

ILOAD1

OUT3

OUT2

OUT1

0.1µF

ILOAD3

ILOAD2

Figure 6. Multiplexed Amplifiers with Power Saving

MAX9934

High-Precision, Low-Voltage, Current-Sense Amplifier

with Current Output and Chip Select for Multiplexing

Maxim Integrated

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.

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

High-Precision, Low-Voltage, Current-Sense Amplifier

with Current Output and Chip Select for Multiplexing

16 Maxim Integrated

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.

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

Maxim Integrated

CS3

CS1

CS2

MICROCONTROLLER

TO EXTERNAL

REFERENCE

VOLTAGE

REF

OUT1

OUT

VCC = 3.3V 0.1µF

VIN1 MAX9934

OUT2

VCC = 3.3V 0.1µF

VIN2

OUT3

VCC = 3.3V 0.1µF

VIN3

MAX9934

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 Maxim Integrated

Chip Information

PROCESS: BiCMOS

RS+

RS-

TOP VIEW

(BUMPS ON BOTTOM)

B2 A2

B3 A3

B1 A1 VCC

OUT

GND

UCSP

MAX9934T/F

N.C.

RS+

RS-OUT

GND

VCC

µMAX

TOP VIEW

MAX9934T/F

Pin Configurations

Package Information

For the latest package outline information and land patterns (foot-

prints), 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 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 ________________________________

MAX9934

High-Precision, Low-Voltage, Current-Sense Amplifier

with Current Output and Chip Select for Multiplexing

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

3 11/12 Added automotive packages to Ordering Information 1