MAX4206ETE+T - Maxim Integrated - Datasheet.Directory

MAX4206 Precision Transimpedance

Logarithmic Amplifier with Over

5 Decades of Dynamic Range

EVALUATION KIT AVAILABLE

General Description

The MAX4206 logarithmic amplifier computes the log

ratio of an input current relative to a reference current

(externally or internally generated) and provides a cor-

responding voltage output with a default 0.25V/decade

scale factor. The device operates from a single +2.7V

to +11V supply or from dual ±2.7V to ±5.5V supplies

and is capable of measuring five decades of input cur-

rent across a 10nA to 1mA range.

The MAX4206’s uncommitted op amp can be used for

a variety of functions, including filtering noise, adding

offset, and adding additional gain. A 0.5V reference is

also included to generate an optional precision current

reference using an external resistor, which adjusts the

log intercept of the MAX4206. The output-offset voltage

and the adjustable scale factor are also set using exter-

nal resistors.

The MAX4206 is available in a space-saving 16-pin

TQFN package (4mm x 4mm x 0.8mm), and is speci-

fied for operation over the -40°C to +85°C extended

temperature range.

Applications

Photodiode Current Monitoring

Portable Instrumentation

Medical Instrumentation

Analog Signal Processing

Benefits and Features

•Single Supply Capability Reduces System Power

Supply Requirements

•+2.7V to +11V Single-Supply Operation

•Also Supports ±2.7V to ±5.5V Dual-Supply

Operation if Required

•Wide Dynamic Range Supports Most Photodiode

Current Measurement Applications

•5 Decades of Dynamic Range (10nA to 1mA)

•Monotonic Over a 1nA to 1mA Range

•Adjustable Output Scale Factor

•0.25V/Decade Internally Trimmed Output Scale

Factor

•Adjustable Output Offset Voltage

•Internal 10nA to 10µA Reference Current Source

•0.5V Input Common-Mode Voltage

•Small Package and Few External Components

Saves Space and Simplifies Design-In

•16-Pin TQFN Package (4mm x 4mm x0.8mm)

Ordering Information

MAX4206

VEE

GND

REFIIN

CMVIN

REFIOUT

LOGIIN

IIN

CMVOUT

REFISET

SCALE

LOGV2

OSADJ

LOGV1

REFVOUT

VCC

RCOMP

CCOMP

RSET

ROS

0.1µF

VOUT

0.1µF

RCOMP

CCOMP

Typical Operating Circuit

PART TEMP RANGE PIN-PACKAGE

MAX4206ETE -40°C to +85°C 16 TQFN-EP*

*EP = Exposed pad.

16 15 14 13

CMVIN

LOGIIN

REFIIN

REFIOUT

VEE

GND

REFVOUT

N.C.

5678

LOGV1

OSADJ

SCALE

LOGV2

MAX4206

THIN QFN

N.C.

VCC

REFISET

CMVOUT

TOP VIEW

(LEADS ON BOTTOM)

Pin Configuration

19-3071; Rev 2; 5/15

MAX4206 Precision Transimpedance

Logarithmic Amplifier with Over

5 Decades of Dynamic Range

Maxim Integrated | 2www.maximintegrated.com

Absolute Maximum Ratings

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.

(All voltages referenced to GND, unless otherwise noted.)

VCC .........................................................................-0.3V to +12V

VEE............................................................................-6V to +0.3V

Supply Voltage (VCC to VEE) .............................................. +12V

REFVOUT ....................................................(VEE - 0.3V) to +3.0V

OSADJ, SCALE, REFISET ...........................(VEE - 0.3V) to +5.5V

REFIIN, LOGIIN ........................................(VEE - 0.3V) to VCMVIN

LOGV1, LOGV2, CMVOUT,

REFIOUT ......................................(VEE - 0.3V) to (VCC + 0.3V)

CMVIN............................................................(VEE - 0.3V) to +1V

Continuous Current (REFIIN, LOGIIN) ................................10mA

Continuous Power Dissipation (TA= +70°C)

16-Pin Thin QFN (derate 16.9mW/°C above +70°C) ....1349mW

Operating Temperature Range ...........................-40°C to +85°C

Junction Temperature .....................................................+150°C

Storage Temperature Range .............................-65°C to +150°C

Lead Temperature (soldering, 10s) .................................+300°C

DC Electrical Characteristics—Single-Supply Operation

(VCC = +5V, VEE = GND = 0V, IREF = 1µA, ILOG = 10µA, LOGV2 = SCALE, LOGV1 = OSADJ, CMVIN = CMVOUT, RSET > 1MΩ,

TA= -40°C to +85°C. Typical values are at TA= +25°C, unless otherwise noted.) (Note 1)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Supply Voltage VCC (Note 2) 2.7 11.0 V

TA = +25°C 3.9 5

Supply Current ICC TA = -40°C to +85°C 7 mA

Minimum 10 nA

LO GIIN C ur r ent Rang e ( N otes 3, 4) ILOG Maximum 1 mA

Minimum 10 nA

RE FIIN C ur r ent Rang e ( N otes 3, 4) IREF Maximum 1 mA

Common-Mode Voltage VCMVOUT 480 500 520 mV

Common-Mode Voltage Input

Range VCMVIN 0.5 1.0 V

TA = +25°C ±2 ±5

Log Conformity Error VLC

IREF = 10nA,

ILOG= 10nA to 1mA,

K = 0.25V/decade

(Note 4) TA = -40°C to +85°C ±10

TA = +25°C 237.5 250 262.5

Logarithmic Slope (Scale Factor) K TA = -40°C to +85°C (Note 4) 231.25 268.75

mV/

decade

Logarithmic Slope (Scale Factor)

Temperature Drift TA = -40°C to +85°C 80

µV/

d ecad e/

°C

Input Offset Voltage VIO TA = +25°C, |VCMVIN - VREFIIN|,

|VCMVIN - VLOGIIN|15mV

Input Offset Voltage Temperature

Drift VIOS |VCMVIN - VREFIIN|, |VCMVIN - VLOGIIN| 6 µV/°C

TA = +25°C 1.218 1.238 1.258

Voltage Reference Output VREFVOUT TA = -40°C to +85°C (Note 4) 1.195 1.275 V

V ol tag e Refer ence O utp ut C ur r ent IREFVOUT 1mA

TA = +25°C 490 500 510

C ur r ent Refer ence O utp ut V ol tag eV

REFISET TA = -40°C to +85°C (Note 4) 482 518 mV

MAX4206 Precision Transimpedance

Logarithmic Amplifier with Over

5 Decades of Dynamic Range

Maxim Integrated | 3www.maximintegrated.com

AC Electrical Characteristics—Single-Supply Operation

(VCC = +5V, VEE = GND = 0, IREF = 1µA, ILOG = 10µA, LOGV2 = SCALE, LOGV1 = OSADJ, CMVIN = CMVOUT, RSET > 1MΩ,

TA= +25°C, unless otherwise noted.)

DC Electrical Characteristics—Single-Supply Operation (continued)

(VCC = +5V, VEE = GND = 0V, IREF = 1µA, ILOG = 10µA, LOGV2 = SCALE, LOGV1 = OSADJ, CMVIN = CMVOUT, RSET > 1MΩ,

TA= -40°C to +85°C. Typical values are at TA= +25°C, unless otherwise noted.) (Note 1)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

LOGV2 BUFFER

TA = +25°C 0.4 2

Input Offset Voltage VIO TA = -40°C to +85°C (Note 4) 6 mV

Input Bias Current IB(Note 4) 0.01 1 nA

VOH RL to GND = 2kΩVCC -

0.2

VCC -

0.3

Output Voltage Range

VOL RL to GND = 2kΩ0.2 0.08

IOUT+ Sourcing 34

Output Short-Circuit Current IOUT- Sinking 58 mA

Slew Rate SR 12 V/µs

Unity-Gain Bandwidth GBW 5 MHz

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

LOGV2 Total Noise 0.1Hz to 10Hz, total output-referred noise,

IREF = 10nA, ILOG = 100nA 17 µVRMS

LOGV2 Spot Noise Density f = 5kHz, IREF = 10nA, ILOG = 100nA 0.8 µV/√Hz

REFVOUT Total Noise 1Hz to 10Hz, total output-referred noise 3.3 µVRMS

REFVOUT Spot Noise Density f = 5kHz 266 nV/√Hz

REFISET Total Noise 1Hz to 10Hz, total output-referred noise 0.67 µVRMS

REFISET Spot Noise Density f = 5kHz 23 nV/√Hz

Small-Signal Unity-Gain

Bandwidth

IREF = 1µA, ILOG = 10µA, RCOMP = 300Ω,

CCOMP = 32pF 1 MHz

DC Electrical Characteristics—Dual-Supply Operation

(VCC = +5V, VEE = -5V, GND = 0, IREF = 1µA, ILOG = 10µA, LOGV2 = SCALE, LOGV1 = OSADJ, CMVIN = CMVOUT, RSET > 1MΩ,

TA= -40°C to +85°C. Typical values are at TA= +25°C, unless otherwise noted.) (Note 1)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

VCC 2.7 5.5

Supply Voltage (Note 2) VEE -2.7 -5.5 V

TA = +25°C 5 6

Supply Current ICC TA = -40°C to +85°C 7.5 mA

Minimum 10 nA

LO GIIN C ur r ent Rang e ( N otes 3, 4) ILOG Maximum 1 mA

Minimum 10 nA

RE FIIN C ur r ent Rang e ( N otes 3, 4) IREF Maximum 1 mA

Common-Mode Voltage VCMVOUT 480 500 520 mV

MAX4206 Precision Transimpedance

Logarithmic Amplifier with Over

5 Decades of Dynamic Range

Maxim Integrated | 4www.maximintegrated.com

DC Electrical Characteristics—Dual-Supply Operation (continued)

(VCC = +5V, VEE = -5V, GND = 0, IREF = 1µA, ILOG = 10µA, LOGV2 = SCALE, LOGV1 = OSADJ, CMVIN = CMVOUT, RSET > 1MΩ,

TA= -40°C to +85°C. Typical values are at TA= +25°C, unless otherwise noted.) (Note 1)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Common-Mode Voltage Input

Range VCMVIN 0.5 1.0 V

TA = +25°C ±2 ±5

Log Conformity Error VLC

IREF = 10nA,

ILOG= 10nA to 1mA,

K = 0.25V/decade

(Note 4) TA = -40°C to +85°C ±10

TA = +25°C 237.5 250 262.5

Logarithmic Slope (Scale Factor) K TA = -40°C to +85°C 231.25 268.75

mV/

decade

Logarithmic Slope (Scale Factor)

Temperature Drift TA = -40°C to +85°C 80

µV/

decade/

°C

Input Offset Voltage VIO TA = +25°C, |VCMVIN - VREFIIN|,

|VCMVIN - VLOGIIN|15mV

Input Offset Voltage

Temperature Drift VIOS |VCMVIN - VREFIIN|, |VCMVIN - VLOGIIN| 6 µV/°C

TA = +25°C 1.218 1.238 1.258

Voltage Reference Output VREFVOUT TA = -40°C to +85°C (Note 4) 1.195 1.275 V

Voltage Reference Output

Current IREFVOUT 1mA

TA = +25°C 490 500 510

Current Reference Output

Voltage VREFISET TA = -40°C to +85°C (Note 4) 482 518 mV

LOGV2 BUFFER

TA = +25°C 0.4 2

Input Offset Voltage VIO TA = -40°C to +85°C (Note 4) 6 mV

Input Bias Current IB(Note 4) 0.01 1 nA

VOH RL to GND = 2kΩVCC -

0.2

VCC -

0.3

Output Voltage Range

VOL RL to GND = 2kΩVEE +

0.2

VEE +

0.08

IOUT+ Sourcing 34

Output Short-Circuit Current IOUT- Sinking 58 mA

Slew Rate SR 12 V/µs

Unity-Gain Bandwidth GBW 5 MHz

MAX4206 Precision Transimpedance

Logarithmic Amplifier with Over

5 Decades of Dynamic Range

Maxim Integrated | 5www.maximintegrated.com

AC Electrical Characteristics—Dual-Supply Operation

(VCC = +5V, VEE = -5V, GND = 0, IREF = 1µA, ILOG = 10µA, LOGV2 = SCALE, LOGV1 = OSADJ, CMVIN = CMVOUT, RSET > 1MΩ,

TA= +25°C, unless otherwise noted.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

LOGV2 Total Noise 0.1Hz to 10Hz, total output-referred noise,

IREF = 10nA, ILOG = 100nA 17 µVRMS

LOGV2 Spot Noise Density f = 5kHz, IREF = 10nA, ILOG = 100nA 0.8 µV/√Hz

REFVOUT Total Noise 1Hz to 10Hz, total output-referred noise 3.3 µVRMS

REFVOUT Spot Noise Density f = 5kHz 266 nV/√Hz

REFISET Total Noise 1Hz to 10Hz, total output-referred noise 0.67 µVRMS

REFISET Spot Noise Density f = 5kHz 23 nV/√Hz

Small-Signal Unity-Gain

Bandwidth

IREF = 1µA, ILOG = 10µA, RCOMP = 300Ω,

CCOMP = 32pF 1MHz

Note 1: All devices are 100% production tested at TA= +25°C. All temperature limits are guaranteed by design.

Note 2: Guaranteed and functionally verified.

Note 3: Log conformity error less than ±5mV with scale factor = 0.25V/decade.

Note 4: Guaranteed by design.

VLOGV1 vs. ILOG

MAX4206 toc01

ILOG (A)

VLOGV1 (V)

1m100μ

100n 1μ10μ

0.25

0.50

0.75

1.00

1.25

1.50

1.75

-0.25

10n 10m

IREF = 10nA

TA = -40°C TO +85°C

VCC = +5V

VEE = GND

1m100μ

10n 100n 1μ10μ

1n 10m

VLOGV1 vs. ILOG

(IREF = 10nA)

MAX4206 toc02

ILOG (A)

VLOGV1 (V)

0.25

0.50

0.75

1.00

1.25

1.50

1.75

-0.25

IREF = 10nA

TA = -40°C TO +85°C

VCC = +5V

VEE = -5V

1m100μ

10n 100n 1μ10μ10m

VLOGV1 vs. ILOG

MAX4206 toc03

ILOG (A)

VLOGV1 (V)

0.25

0.50

0.75

1.00

1.25

1.50

1.75

-0.25

IREF = 10nA

TA = -40°C TO +85°C

VCC = +2.7V

VEE = GND

Typical Operating Characteristics

(VCC = +5V, VEE = GND = 0V, IREF = 1µA, ILOG = 10µA, LOGV2 = SCALE, LOGV1 = OSADJ, CMVIN = CMVOUT, RSET > 1MΩ,

TA= +25°C, unless otherwise noted.)

MAX4206 Precision Transimpedance

Logarithmic Amplifier with Over

5 Decades of Dynamic Range

Maxim Integrated | 6www.maximintegrated.com

-0.25

0.25

0.50

0.75

1.00

1.25

1.50

1.75

2.00

-0.50

VLOGV1 vs. ILOG

(IREF = 10nA TO 1mA)

MAX4206 toc04

ILOG (A)

VLOGV1 (V)

1m100μ

100n 1μ10μ

10n 10m

10nA

100nA

1μA

10μA

100μA

1mA

VLOGV1 vs. IREF

(ILOG = 10nA TO 1mA)

MAX4206 toc05

IREF (A)

VLOGV1 (V)

100μ

10μ

1μ

100n10n

-0.25

0.25

0.50

0.75

1.00

1.25

1.50

1.75

2.00

-0.50

1n 1m

1μA10μA100μA

1mA

100nA

10nA

-15

-10

-5

-20

NORMALIZED LOG CONFORMANCE

ERROR vs. ILOG

MAX4206 toc06

ILOG (A)

ERROR (mV)

1m100μ

100n 1μ10μ

10n 10m

IREF = 10nA

TA = -40°C TO +85°C

VCC = +5V

VEE = GND

TA = -40°C

1m100μ

10n 100n 1μ10μ

1n 10m

-15

-10

-5

-20

NORMALIZED LOG CONFORMANCE

ERROR vs. ILOG

MAX4206 toc07

ILOG (A)

ERROR (mV)

IREF = 10nA

TA = -40°C TO +85°C

VCC = +5V

VEE = -5V

TA = -40°C

-15

-10

-5

-20

NORMALIZED LOG CONFORMANCE

ERROR vs. ILOG

MAX4206 toc08

ILOG (A)

ERROR (mV)

1m100μ

100n 1μ10μ

10n 10m

IREF = 10nA

TA = -40°C TO +85°C

VCC = +2.7V

VEE = GND

TA = -40°C

-15

-10

-5

-20

NORMALIZED LOG CONFORMANCE

ERROR vs. ILOG

MAX4206 toc09

ILOG (A)

ERROR (mV)

1m100μ

100n 1μ10μ

10n 10m

IREF = 10nA

SINGLE SUPPLY: VCC = +2.7V, +5V, 11V,

VEE = GND

DUAL SUPPLY: VCC = +5V

VEE = -5V

VLOGIIN - VCMVIN vs. ILOG

MAX4206 toc10

ILOG (A)

VLOGIIN - VCMVIN (mV)

1m100μ100n 1μ10μ

-1

-2

-3

-4

-5

10n1n 10m

IREF = 10nA

LOGV2

vs. FREQUENCY

MAX4206 toc11

FREQUENCY (Hz)

1M100k10k1k10010

0.1

0.01

110M

NOISE DENSITY (μV/√Hz)

IREF = ILOG

100nA

10nA

1μA

10μA

AT VLOGV2 vs. ILOG

MAX4206 toc12

ILOG (A)

VOLTAGE NOISE (mVRMS)

100μ10μ1μ100n

10n 1m

IREF = ILOG

f = 1Hz TO 1MHz

Typical Operating Characteristics (continued)

(VCC = +5V, VEE = GND = 0V, IREF = 1µA, ILOG = 10µA, LOGV2 = SCALE, LOGV1 = OSADJ, CMVIN = CMVOUT, RSET > 1MΩ,

TA= +25°C, unless otherwise noted.)

MAX4206 Precision Transimpedance

Logarithmic Amplifier with Over

5 Decades of Dynamic Range

Maxim Integrated | 7www.maximintegrated.com

ILOG PULSE RESPONSE

(IREF = 100nA,

VCC = 5V, VEE = GND)

MAX4206 toc13

VLOGV1 (V)

20μs/div

0.50V

1.0V 100μA TO 1mA

10μA TO 100μA

1μA TO 10μA

100nA TO 1μA

0.25V

0.75V

0.50V

0.25V

ILOG PULSE RESPONSE

(IREF = 100nA,

VCC = 5V, VEE = -5V)

MAX4206 toc14

VLOGV1 (V)

20μs/div

0.50V

1.0V 100μA TO 1mA

10μA TO 100μA

1μA TO 10μA

100nA TO 1μA

0.25V

0.75V

0.50V

0.25V

IREF PULSE RESPONSE

(ILOG = 1mA)

MAX4206 toc15

VLOGV1 (V)

20μs/div

0.50V

1.0V 1μA TO 100nA

10μA TO 1μA

100μA TO 10μA

1mA TO 100μA

0.25V

0.75V

0.50V

0.25V

240 250245 255

LOGARITHMIC SLOPE DISTRIBUTION

MAX4206 toc16

SLOPE (mV/DECADE)

COUNT (%)

260

1.232 1.238 1.2401.234 1.236 1.242

VREFVOUT DISTRIBUTION

MAX4206 toc17

VREFVOUT (V)

COUNT (%)

RL = 100kΩ

1.244

-1.0 0.5 1.0-0.5 0 1.5 2.0 2.5

INPUT OFFSET VOLTAGE DISTRIBUTION

MAX4206 toc18

INPUT OFFSET VOLTAGE (mV)

COUNT (%)

INPUT OFFSET VOLTAGE = VLOGIIN - VCMVIN

3.0

Typical Operating Characteristics (continued)

(VCC = +5V, VEE = GND = 0V, IREF = 1µA, ILOG = 10µA, LOGV2 = SCALE, LOGV1 = OSADJ, CMVIN = CMVOUT, RSET > 1MΩ,

TA= +25°C, unless otherwise noted.)

MAX4206 Precision Transimpedance

Logarithmic Amplifier with Over

5 Decades of Dynamic Range

Maxim Integrated | 8www.maximintegrated.com

-100

10 100 1k 10k 100k 1M

REFERENCE POWER-SUPPLY

REJECTION RATIO vs. FREQUENCY

-80

MAX4206 toc23

FREQUENCY (Hz)

REFERENCE PSRR (dB)

-60

-40

-20

-90

-70

-50

-30

-10 CREFVOUT = 0.1μF

IREFVOUT = 1mA

REFERENCE LINE-TRANSIENT RESPONSE

MAX4206 toc24

10μs/div

1.238V

VCC

2V/div

VREFVOUT

200mV/div

CREFVOUT = 0F

REFERENCE LOAD-TRANSIENT RESPONSE

MAX4206 toc25

100μs/div

1.238V

0mA

IREFVOUT

1mA/div

VREFVOUT

100mV/div

CREFVOUT = 0F

REFERENCE TURN-ON TRANSIENT RESPONSE

MAX4206 toc26

10μs/div

VCC

2.5V/div

VREFVOUT

500mV/div

-10

-4

-6

-8

-2

-50 0-25 25 50 75 100

OUTPUT OFFSET VOLTAGE

vs. TEMPERATURE

MAX4206 toc19

TEMPERATURE (°C)

VLOGV1 (mV)

IREF = 1μA

ILOG 1μA

1.20

1.23

1.22

1.21

1.24

1.25

1.26

1.27

1.28

1.29

1.30

-50 0-25 25 50 75 100

REFERENCE OUTPUT VOLTAGE (VREFVOUT)

vs. TEMPERATURE

MAX4206 toc20

TEMPERATURE (°C)

REFERENCE OUTPUT VOLTAGE (V)

1.20

1.23

1.22

1.21

1.24

1.25

1.26

1.27

1.28

1.29

1.30

-1.0 -0.5 0.501.0

REFERENCE OUTPUT VOLTAGE (VREFVOUT)

vs. LOAD CURRENT

MAX4206 toc21

LOAD CURRENT (mA)

REFERENCE OUTPUT VOLTAGE (V)

1.200

1.215

1.210

1.205

1.220

1.225

1.230

1.235

1.240

1.245

1.250

-1.0 -0.5 0.501.0

REFERENCE OUTPUT VOLTAGE (VREFVOUT)

vs. SUPPLY VOLTAGE

MAX4206 toc22

LOAD CURRENT (mA)

REFERENCE OUTPUT VOLTAGE (V)

Typical Operating Characteristics (continued)

(VCC = +5V, VEE = GND = 0V, IREF = 1µA, ILOG = 10µA, LOGV2 = SCALE, LOGV1 = OSADJ, CMVIN = CMVOUT, RSET > 1MΩ,

TA= +25°C, unless otherwise noted.)TA= +25°C, unless otherwise noted.)

MAX4206 Precision Transimpedance

Logarithmic Amplifier with Over

5 Decades of Dynamic Range

Maxim Integrated | 9www.maximintegrated.com

SMALL-SIGNAL AC RESPONSE

ILOG TO VLOGV1

MAX4206 toc27

FREQUENCY (Hz)

NORMALIZED GAIN (dB)

1M100k10k1k

-50

-40

-30

-20

-10

-60

100 10M

ILOG = 100μA

ILOG = 1mA

ILOG = 10μA

ILOG = 1μA

ILOG = 100nA

CCOMP = 33pF

RCOMP = 330Ω

SMALL-SIGNAL AC RESPONSE

ILOG TO VLOGV1

MAX4206 toc28

FREQUENCY (Hz)

NORMALIZED GAIN (dB)

1M100k10k1k

-50

-40

-30

-20

-10

-60

100 10M

ILOG = 100μA

ILOG = 1mA

ILOG = 10μA

ILOG = 1μA

ILOG = 100nA

CCOMP = 100pF

RCOMP = 1kΩ

SMALL-SIGNAL AC RESPONSE

OF BUFFER

MAX4206 toc29

FREQUENCY (Hz)

NORMALIZED GAIN (dB)

10M1M100k

-9

-6

-3

-12

10k 100M

AV = 2V/V

AV = 4V/V

AV = 1V/V

Pin Description

PIN NAME FUNCTION

1, 9 N.C. No Connection. Not internally connected.

2 REFVOUT 1.238V Reference Voltage Output. Bypass REFVOUT to GND with a 0 to 1µF capacitor (optional).

3 GND Ground

EE Negative Power Supply. Bypass VEE to GND with a 0.1µF capacitor.

5 LOGV1 Logarithmic Amplifier Voltage Output 1. The output scale factor of LOGV1 is 0.25V/decade.

6 OSADJ Offset Adjust Input. When operating from a single power supply, current applied to OSADJ adjusts

the output offset voltage (see the Output Offset section).

7 SCALE Scale Factor Input. Adjust the output scale factor for LOGV2 using a resistive divider (see the Scale

Factor section).

8 LOGV2 Logarithmic Amplifier Voltage Output 2. Adjust the output scale factor for LOGV2 using a resistive

divider (see the Scale Factor section).

10 VCC Positive Power Supply. Bypass VCC to GND with a 0.1µF capacitor.

11 REFISET Current Reference Adjust Input. A resistor (RSET), from REFISET to GND, adjusts the current at

REFIOUT (see the Adjusting the Logarithmic Intercept section).

12 CMVOUT 0.5V Common-Mode Voltage Reference Output. Bypass CMVOUT to GND with a 0.1µF capacitor.

13 REFIOUT Current Reference Output. The internal current reference output is available at REFIOUT.

14 REFIIN Current Reference Input. Apply an external reference current at REFIIN. IREFIIN is the reference

current used by the logarithmic amplifier when generating LOGV1.

15 LOGIIN Current Input to Logarithmic Amplifier. LOGIIN is typically connected to a photodiode anode or other

external current source.

16 CMVIN Common-Mode Voltage Input. VCMVIN is the common-mode voltage for the input and reference

amplifiers (see the Common Mode section).

Typical Operating Characteristics (continued)

(VCC = +5V, VEE = GND = 0V, IREF = 1µA, ILOG = 10µA, LOGV2 = SCALE, LOGV1 = OSADJ, CMVIN = CMVOUT, RSET > 1MΩ,

TA= +25°C, unless otherwise noted.)TA= +25°C, unless otherwise noted.)

MAX4206 Precision Transimpedance

Logarithmic Amplifier with Over

5 Decades of Dynamic Range

Maxim Integrated | 10www.maximintegrated.com

Detailed Description

Theory

Figure 2 shows a simplified model of a logarithmic

amplifier. Two transistors convert the currents applied

at LOGIIN and REFIIN to logarithmic voltages accord-

ing to the following equation:

where:

VBE = base-emitter voltage of a bipolar transistor

k = 1.381 x 10-23 J/K

T = absolute temperature (K)

q = 1.602 x 10 –19 C

IC= collector current

IS= reverse saturation current

The logarithmic amplifier compares VBE1 to the refer-

ence voltage VBE2, which is a logarithmic voltage for a

known reference current, IREF. The temperature depen-

dencies of a logarithmic amplifier relate to the thermal

voltage, (kT/q), and IS. Matched transistors eliminate

the IStemperature dependence of the amplifier in the

following manner:

VVV

OUT BE BE

LOG

REF

LOG

REF

LOG

REF

=−

=⎛

⎝

⎜⎞

⎠

⎟⎛

⎝

⎜⎞

⎠

⎟−⎛

⎝

⎜⎞

⎠

⎟⎛

⎝

⎜⎞

⎠

⎟

=⎛

⎝

⎜⎞

⎠

⎟⎛

⎝

⎜⎞

⎠

⎟−⎛

⎝

⎜⎞

⎠

⎟

⎡

⎣

⎢

⎤

⎦

⎥

=⎛

⎝

⎜⎞

⎠

⎟⎛

⎝

⎜⎞

⎠

⎟

⎡

⎣

⎢

ln ln

ln ⎤⎤

⎦

⎥

=⎛

⎝

⎜⎞

⎠

⎟

()

⎛

⎝

⎜⎞

⎠

⎟

⎡

⎣

⎢

⎤

⎦

⎥

=× ⎛

⎝

⎜⎞

⎠

⎟

Isee Figure

LOG

REF

LOG

REF

ln( ) log

log ( )

VkT

BE C

=⎛

⎝

⎜⎞

⎠

⎟⎛

⎝

⎜⎞

⎠

⎟

MAX4206

LOGIIN

CMVIN

VCC

REFIIN

VCC

CURRENT

CORRECTION

VCC

LOGV1

SCALE

OSADJ

LOGV2

VCC

REFISET

CURRENT MIRROR

CMVOUTREFVOUT

REFIOUT

GND

VEE

0.5V

1.238V

VEE

SUMMING

AMPLIFIER

AND

TEMPERATURE

COMPENSATION

Figure 1. Functional Diagram

MAX4206 Precision Transimpedance

Logarithmic Amplifier with Over

5 Decades of Dynamic Range

Maxim Integrated | 11www.maximintegrated.com

where:

K = scale factor (V/decade)

ILOG = the input current at LOGIIN

IREF = the reference current at REFIIN

The MAX4206 uses internal temperature compensation

to virtually eliminate the effects of the thermal voltage,

(kT/q), on the amplifier’s scale factor, maintaining a

constant slope over temperature.

Definitions

Transfer Function

The ideal logarithmic amplifier transfer function is:

Adjust K (see the

Scale Factor

section) to increase the

transfer-function slope as illustrated in Figure 3. Adjust

IREF using REFISET (see the

Adjusting the Logarithmic

Intercept

section) to shift the logarithmic intercept to the

left or right as illustrated in Figure 4.

Log Conformity

Log conformity is the maximum deviation of the

MAX4206’s output from the best-fit straight line of the

VLOGV1 versus log (ILOG/IREF) curve. It is expressed as

a percent of the full-scale output or an output voltage.

Referred-to-Input and Referred-to-Output Errors

The log nature of the MAX4206 insures that any addi-

tive error at LOGV1 corresponds to multiplicative error

at the input, regardless of input level.

Total Error

Total error (TE) is defined as the deviation of the output

voltage, VLOGV1, from the ideal transfer function (see

the

Transfer Function

section):

Total error is a combination of the associated gain,

input offset current, input bias current, output offset

voltage, and transfer characteristic nonlinearity (log

conformity) errors:

where VLC and VOSOUT are the log conformity and out-

put offset voltages, respectively. Output offset is

defined as the offset occurring at the output of the

MAX4206 when equal currents are presented to ILOG

and IREF. Because the MAX4206 is configured with

a gain of K = 0.25V/decade, a 4 should multiply the

(±VLC ±VOSOUT) term, if VLC and VOSOUT were derived

from this default configuration.

VKKII

II VV

LOGV LOG BIAS

REF BIAS LC OSOUT210

14=± −

−

⎛

⎝

⎜⎞

⎠

⎟±± ±

()

⎡

⎣

⎢

⎤

⎦

⎥

( ) logΔ

VVTE

LOGV IDEAL1=±

VK I

IDEAL LOG

REF

=× ⎛

⎝

⎜⎞

⎠

⎟

log10

LOGIIN

CMVIN

VCC

REFIIN

VCC

VBE1

VBE2

VEE

ILOG

IREF

Figure 2. Simplified Model of a Logarithmic Amplifier

IDEAL TRANSFER FUNCTION

WITH VARYING K

MAX4206 fig03

CURRENT RATIO (ILOG/IREF)

NORMALIZED OUTPUT VOLTAGE (V)

100.1

-2

-3

-1

-4

0.001 1000

VOUT = K LOG (ILOG/IREF)K = 1

K = 0.5

K = 0.25

Figure 3. Ideal Transfer Function with Varying K

MAX4206 Precision Transimpedance

Logarithmic Amplifier with Over

5 Decades of Dynamic Range

Maxim Integrated | 12www.maximintegrated.com

IBIAS1 and IBIAS2 are currents in the order of 20pA, sig-

nificantly smaller than ILOG and IREF, and can therefore

be eliminated:

Expanding this expression:

The first term of this expression is the ideal component

of VLOGV1. The remainder of the expression is the TE:

In the second term, one can generally remove the

products relating to ΔK, because ΔK is generally much

less than 1. Hence, a good approximation for TE is

given by:

As an example, consider the following situation:

Full-scale input = 5V

ILOG = 100µA

IREF = 100nA

K = 1 ±5% V/decade (note that the uncommitted ampli-

fier is configured for a gain of 4)

VLC = ±5mV (obtained from the

Electrical Character-

istics

table)

VOSOUT = ±2mV (typ)

TA= +25°C

Substituting into the total error approximation,

TE ≅± (1V/decade)(0.05log10 (100µA/100nA)

±4 (±5mV ±2mV) = ±[0.15V ±4(±7mV)]

As a worst case, one finds TE ≅±178mV or ±3.6% of

full scale.

When expressed as a voltage, TE increases in proportion

with an increase in gain as the contributing errors are

defined at a specific gain. Calibration using a look-up

table eliminates the effects of gain and output offset

errors, leaving conformity error as the only factor con-

tributing to total error. For further accuracy, consider tem-

perature monitoring as part of the calibration process.

Applications Information

Input Current Range

Five decades of input current across a 10nA to 1mA

range are acceptable for ILOG and IREF. The effects of

leakage currents increase as ILOG and IREF fall below

10nA. Bandwidth decreases at low ILOG values (see

the

Frequency Response and Noise Considerations

section). As ILOG and IREF increase to 1mA or higher,

transistors become less logarithmic in nature. The

MAX4206 incorporates leakage current compensation

and high-current correction circuits to compensate for

these errors.

Frequency Compensation

The MAX4206’s frequency response is a function of the

input current magnitude and the selected compensation

network at LOGIIN and REFIIN. The compensation net-

work comprised of CCOMP and RCOMP ensures stability

over the specified range of input currents by introducing

an additional pole/zero to the system. For the typical

application, select CCOMP = 100pF and RCOMP = 100Ω.

Where high bandwidth at low current is required, CCOMP

= 32pF and RCOMP = 330Ωare suitable compen-

sation values.

TE K K I

IVV

LOG

REF LC OSOUT

≅± ⎛

⎝

⎜⎞

⎠

⎟±± ±

()

⎡

⎣

⎢

⎤

⎦

⎥

Δlog10 4

TE K K I

IKKVV

LOG

REF LC OSOUT

≅± ⎛

⎝

⎜⎞

⎠

⎟±±±±

()

ΔΔlog ( )

10 41

IKK I

KKVV

LOGV LOG

REF

LOG

REF

LC OSOUT

210 10

≅⎛

⎝

⎜⎞

⎠

⎟±⎛

⎝

⎜⎞

⎠

⎟

±±±±

()

log log

( )

VKKI

IVV

LOGV LOG

REF LC OSOUT210

14≅± ⎛

⎝

⎜⎞

⎠

⎟±± ±

()

⎡

⎣

⎢

⎤

⎦

⎥

( ) logΔ

IDEAL TRANSFER FUNCTION

WITH VARYING IREF

MAX4206 fig04

ILOG (A)

OUTPUT VOLTAGE (V)

100μ

1μ10μ100n10n

-1.0

-0.5

0.5

1.0

1.5

-1.5

1n 1m

IREF = 100μA

IREF = 1μA

IREF = 10nA

Figure 4. Ideal Transfer Function with Varying IREF

MAX4206 Precision Transimpedance

Logarithmic Amplifier with Over

5 Decades of Dynamic Range

Maxim Integrated | 13www.maximintegrated.com

Frequency Response and Noise Considerations

The MAX4206 bandwidth is proportional to the magni-

tude of the IREF and ILOG currents, whereas the noise is

inversely proportional to IREF and ILOG currents.

Common Mode

A common-mode input voltage, VCMVOUT, of 0.5V is

available at CMVOUT and can be used to bias the log-

ging and reference amplifier inputs by connecting

CMVOUT to CMVIN. An external voltage between 0.5V

and 1V can be applied to CMVIN to bias the logging

and reference transistor collectors and to optimize the

performance required for both single- and dual-supply

operation.

Adjusting the Logarithmic Intercept

Adjust the logarithmic intercept by changing the refer-

ence current, IREF. A resistor from REFISET to GND

(see Figures 5 and 6) adjusts the reference current,

according to the following equation:

where VREFISET is 0.5V. Select RSET between 5kΩand

5MΩ. REFIOUT current range is 10nA to 10µA only.

Single-Supply Operation

When operating from a single +2.7V to +11V supply,

ILOG must be greater than IREF, resulting in a positive

slope of the log output voltages, LOGV1 and LOGV2.

Bias the log and reference amplifiers by connecting

CMVOUT to CMVIN or connecting an external voltage

reference between 0.5V and 1V to CMVIN. For single-

supply operation, connect VEE to GND.

Output Offset

Select ROS and IOS to adjust the output offset voltage

(see Figure 5). The magnitude of the offset voltage is

given by:

VOS = ROS ✕IOSADJ

Scale Factor

The scale factor, K, is the slope of the logarithmic out-

put. For the LOGV1 amplifier, K = 0.25V/decade. When

operating in a single-supply configuration, adjust the

overall scale factor for the MAX4206 using the uncom-

mitted LOGV2 amplifier and the following equation,

which refers to Figure 5:

Select R1 between 1kΩand 100kΩ, with an ideal value

of 10kΩ. The noninverting amplifier ensures that the

overall scale factor is greater than or equal to

0.25V/decade for single-supply operation.

Design Example

Desired:

Single-Supply Operation

Logarithmic intercept: 100nA

Overall scale factor = 1V/decade

Because there is no offset current applied to the circuit

(ROS = 0Ω), the reference current, IREF, equals the log

intercept of 100µA. Therefore,

Select R1= 10kΩ:

Dual-Supply Operation

When operating from dual ±2.7 to ±5.5V supplies, it is

not required that ILOG be greater than IREF. A positive

output voltage results at LOGV1 when ILOG exceeds

IREF. A negative output voltage results at LOGV1 when

ILOG is less than IREF. Bias the log and reference

amplifiers by connecting CMVOUT to CMVIN or con-

nect an external 0.5V to 1V reference to CMVIN. For

dual-supply operation with CMVIN < 0.5V, refer to the

MAX4207 data sheet.

Output Offset

The uncommitted amplifier in the inverting configuration

utilized by the MAX4206 facilitates large output-offset

voltage adjustments when operated with dual supplies.

The magnitude of the offset voltage is given by the fol-

lowing equation:

A resistive divider between REFVOUT, OSADJ, and

GND can be used to adjust VOSADJ (see Figure 6).

VV R

OSADJ REFOUT

⎛

⎝

⎜⎞

⎠

⎟

VV R

OS OSADJ

⎛

⎝

⎜⎞

⎠

⎟

VV k210 1

025 130=−

⎛

⎝

⎜⎞

⎠

⎟=ΩΩ

nA k

SET =×=

10 100 500

.Ω

RR K

025 1=−

⎛

⎝

⎜⎞

⎠

⎟

SET REFISET

REF

=×10

MAX4206 Precision Transimpedance

Logarithmic Amplifier with Over

5 Decades of Dynamic Range

Maxim Integrated | 14www.maximintegrated.com

Scale Factor

The scale factor, K, is the slope of the logarithmic output.

For the LOGV1 amplifier, K = 0.25V/decade. When oper-

ating from dual supplies, adjust the overall scale factor

for the MAX4206 using the uncommitted LOGV2 amplifi-

er and the following equation, which refers to Figure 6:

Select R2between 1kΩand 100kΩ.

Design Example

Desired:

Dual-Supply Operation

Logarithmic intercept: 1µA

Overall scale factor = 1V/decade

Select R1= 10kΩ:

Measuring Optical Absorbance

A photodiode provides a convenient means of measur-

ing optical power, as diode current is proportional to

the incident optical power. Measure absolute optical

power using a single photodiode connected at LOGIIN,

with the MAX4206’s internal current reference driving

REFIIN. Alternatively, connect a photodiode to each of

the MAX4206’s logging inputs, LOGIIN and REFIIN, to

measure relative optical power (Figure 7).

In absorbance measurement instrumentation, a refer-

ence light source is split into two paths. The unfiltered

path is incident upon the photodiode of the reference

channel, REFIIN. The other path passes through a sam-

ple of interest, with the resulting filtered light incident on

the photodiode of the second channel, LOGIIN. The

MAX4206 outputs provide voltages proportional to the

log ratio of the two optical powers—an indicator of the

optical absorbance of the sample.

In wavelength-locking applications, often found in

fiberoptic communication modules, two photodiode cur-

rents provide a means of determining whether a given

optical channel is tuned to the desired optical frequency.

In this application, two bandpass optical filters with over-

lapping “skirts” precede each photodiode. With proper fil-

ter selection, the MAX4206 output can vary monotonically

(ideally linearly) with optical frequency.

RkV decade k210 1

025 40=×

⎛

⎝

⎜⎞

⎠

⎟=ΩΩ

SET =×=

10 1 50

μΩ

RRK

025

=⎛

⎝

⎜⎞

⎠

⎟

MAX4206

VEE

GND

REFIIN

LOGIIN

IIN

CMVIN

REFIOUT

CMVOUT

REFISET

SCALE

LOGV2

OSADJ

LOGV1

REFVOUT

VCC

RCOMP

100Ω

CCOMP

100pF

RSET

500kΩ

ROS

0Ω

10kΩ

30kΩ

0.1μF

VOUT

0.1μF

RCOMP

100Ω

CCOMP

100pF

Figure 5. Single-Supply Typical Operating Circuit

MAX4206

VEE

GND

REFIIN

REFIOUT

LOGIIN

IIN

REFISET

SCALE

LOGV2

LOGV1

CMVIN

CMVOUT

VCC

RCOMP

100Ω

CCOMP

100pF

RSET

50kΩ

10kΩ

40kΩ

0.1μF

VOUT

RCOMP

100Ω

CCOMP

100pF

OSADJ

REFVOUT

Figure 6. Dual-Supply Typical Operating Circuit

MAX4206 Precision Transimpedance

Logarithmic Amplifier with Over

5 Decades of Dynamic Range

Maxim Integrated | 15www.maximintegrated.com

Photodiode Current Monitoring

Figure 8 shows the MAX4206 in a single-supply, optical-

power measurement circuit, common in fiberoptic

applications. The MAX4007 current monitor converts

the sensed APD current to an output current that drives

the MAX4206 LOGIIN input (APD current is scaled by

0.1). The MAX4007 also buffers the high-voltage APD

voltages from the lower MAX4206 voltages. The

MAX4206’s internal current reference sources 10nA

(RSET = 5MΩ) to the REFIIN input. This configuration

sets the logarithmic intercept to 10nA, corresponding to

an APD current of 100nA. The unity-gain configuration

of the output buffer maintains the 0.25V/decade gain

present at the LOGV1 output.

Capacitive Loads

The MAX4206 drives capacitive loads of up to 50pF.

Reactive loads decrease phase margin and can pro-

duce excessive ringing and oscillation. Use an isolation

resistor in series with LOGV1 or LOGV2 to reduce the

effect of large capacitive loads. Recall that the combi-

nation of the capacitive load and the small isolation

resistor limits AC performance.

Power Dissipation

The LOGV1 and LOGV2 amplifiers are capable of

sourcing or sinking in excess of 30mA. Ensure that the

continuous power dissipation rating for the MAX4206 is

not exceeded.

TQFN Package

The 16-lead thin QFN package has an exposed paddle

that provides a heat-removal path, as well as excellent

electrical grounding to the PC board. The MAX4206’s

exposed pad is internally connected to VEE, and can

either be connected to the PC board VEE plane or left

unconnected. Ensure that only VEE traces are routed

under the exposed paddle.

Layout and Bypassing

Bypass VCC and VEE to GND with ceramic 0.1µF

capacitors. Place the capacitors as close to the device

as possible. Bypass REFVOUT and/or CMVOUT to

GND with a 0.1µF ceramic capacitor for increased

noise immunity and a clean reference current. For low-

current operation, it is recommended to use metal

guard rings around LOGIIN, REFIIN, and REFISET.

Connect this guard ring to CMVOUT.

Evaluation Kit

An evaluation kit is available for the MAX4206. The kit is

flexible and can be configured for either single-supply

or dual-supply operation. The scale factor and refer-

ence current are selectable. Refer to the MAX4206

Evaluation Kit data sheet for more information.

Chip Information

TRANSISTOR COUNT: 754

PROCESS: BiCMOS

MAX4206

VEE

GND

0.1μF

REFIIN

LOGIIN

VCC

CMVIN

REFIOUT

CMVOUT

REFISET

VCC

SCALE

LOGV1

LOGV2

OSADJ

REFVOUT

100pF

100Ω

100pF

Figure 7. Measuring Optical Absorbance

MAX4206 Precision Transimpedance

Logarithmic Amplifier with Over

5 Decades of Dynamic Range

Maxim Integrated | 16www.maximintegrated.com

VEE

GND

REFVOUT

CMVIN

REFIOUT

CMVOUT

REFISET

VCC

SCALE

LOGV2

OSADJ

LOGV1

REFIIN

FIBER CABLE APD

+2.7V TO +76V 2.2μH

2.2μF 0.22μF

BIAS

REF

CLAMP

OUT

TIA

GND

TO LIMITING

AMPLIFIER

HIGH-SPEED DATA PATH

0.1μF

100pF

VCC

5MΩ

100pF

100Ω

OUTPUT

PHOTODIODE BIAS

0.1μF

IAPD/10

IAPD

0.1μF

MAX4206

MAX4007

Figure 8. Logarithmic Current-Sensing Amplifier with Sourcing Input

PACKAGE

TYPE

PACKAGE

CODE

OUTLINE

NO.

LAND

PATTERN NO.

16 TQFN-EP T1644-4 21-0139 90-0070

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.

MAX4206 Precision Transimpedance

Logarithmic Amplifier with Over

5 Decades of Dynamic Range

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.

For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.

REVISION

NUMBER

REVISION

DATE

DESCRIPTION

PAGES

CHANGED

2 5/15 Updated Benefits and Features section 1

Revision History

Mouser Electronics

Authorized Distributor

Click to View Pricing, Inventory, Delivery & Lifecycle Information:

Maxim Integrated:

MAX4206ETE+ MAX4206ETE+T