ANALOG DEVICES AD8476 Service Manual

Low Power, Unity Gain, Fully Differential

AD8476

10kΩ

10kΩ 10kΩ

INN

1

+V

S

2

VOCM

3

+OUT

4

INP8–V

S

7

NC 6

–OUT 5

NOTES

1. NC = NO CONNECT . DO NOT CONNECT TO THIS PIN.

10195-001

AD8476

Data Sheet

FEATURES

Very low power

330 μA supply current Fully differential or single-ended inputs/outputs Differential output designed to drive precision ADCs

Drives switched capacitor and Σ-Δ ADCs

Rail-to-rail outputs VOCM pin adjusts output common mode Robust overvoltage up to 18 V beyond supplies High performance

Suitable for driving 16-bit converter up to 250 kSPS

39 nV/√Hz output noise

1 ppm/°C gain drift maximum

200 μV maximum output offset

10 V/μs slew rate

5 MHz bandwidth Single supply: 3 V to 18 V Dual supplies: ±1.5 V to ±9 V

Amplifier and ADC Driver

FUNCTIONAL BLOCK DIAGRAM

Figure 1.

APPLICATIONS

ADC driver Differential instrumentation amplifier building block Single-ended-to-differential converter Battery-powered instruments

GENERAL DESCRIPTION

The AD8476 is a very low power, fully differential precision amplifier with integrated gain resistors for unity gain. It is an ideal choice for driving low power, high performance ADCs as a single-ended-to-differential or differential-to-differential amplifier. It provides a precision gain of 1, common-mode level shifting, low temperature drift, and rail-to-rail outputs for maximum dynamic range.

The AD8476 also provides overvoltage protection from large industrial input voltages up to ±23 V while operating on a dual 5 V supply. Power dissipation on a single 5 V supply is only 1.5 mW.

The AD8476 works well with SAR, Σ-Δ, and pipeline converters. The high current output stage of the part allows it to drive the

switched capacitor front-end circuits of many ADCs with minimal error.

Unlike many differential drivers on the market, the AD8476 is a high precision amplifier. With 200 µV maximum output offset, 39 nV/√Hz noise, and −102 dB THD + N at 10 kHz, the

AD8476 pairs well with low power, high accuracy converters.

Considering its low power consumption and high precision, the slew-enhanced AD8476 has excellent speed, settling to 16-bit precision for 250 kSPS acquisition times.

The AD8476 is available in a space-saving 8-lead MSOP package. It is fully specified over the −40°C to +125°C temperature range.

Rev. A

Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without n otice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners.

www.analog.com

AD8476 Data Sheet

TABLE OF CONTENTS

Features .............................................................................................. 1

Applications ....................................................................................... 1

Functional Block Diagram .............................................................. 1

General Description ........................................................................... 1

Revision History ............................................................................... 2

Specifications ..................................................................................... 3

Absolute Maximum Ratings ............................................................ 5

Thermal Resistance ...................................................................... 5

Maximum Power Dissipation ..................................................... 5

ESD Caution .................................................................................. 5

Pin Configuration and Function Descriptions ............................. 6

Typical Performance Characteristics ............................................. 7

Terminology .................................................................................... 15

REVISION HISTORY

11/11—Rev. 0 to Rev. A

Changes to Table 1 ............................................................................ 3

Changes to Typical Performance Characteristics ......................... 7

Added Figure 39; Renumbered Sequentially .............................. 13

Added Table 5 .................................................................................. 18

Removed Low Power ADC Driving Section ............................... 19

Removed Figure 52 ......................................................................... 19

10/11—Revision 0: Initial Version

Theory of Operation ...................................................................... 16

Overview ..................................................................................... 16

Circuit Information .................................................................... 16

DC Precision ............................................................................... 16

Input Voltage Range ................................................................... 17

Driving the AD8476................................................................... 17

Power Supplies ............................................................................ 17

Applications Information .............................................................. 18

Typical Configuration ................................................................ 18

Single-Ended-to-Differential Conversion ............................... 18

Setting the Output Common-Mode Voltage .......................... 18

Outline Dimensions ....................................................................... 19

Ordering Guide .......................................................................... 19

Rev. A | Page 2 of 20

Data Sheet AD8476

SPECIFICATIONS

VS = +5 to ±5 V, VOCM = midsupply, V otherwise noted.

Table 1.

Parameter Test Conditions/Comments

DYNAMIC PERFORMANCE

−3 dB Small Signal Bandwidth V

−3 dB Large Signal Bandwidth V Slew Rate V Settling Time to 0.01% V Settling Time to 0.001% V

NOISE/DISTORTION1

THD + N f = 10 kHz, V

HD2 f = 10 kHz, V HD3 f = 10 kHz, V IMD3 f1 = 95 kHz, f2 = 105 kHz,

Output Voltage Noise f = 0.1 Hz to 10 Hz 6 6 µV p-p Spectral Noise Density f = 10 kHz 39 39 nV/√Hz

GAIN 1 1 V/V

Gain Error RL = ∞ 0.02 0.04 % Gain Drift −40°C ≤ TA ≤ +125°C 1 1 ppm/°C Gain Nonlinearity V

OFFSET AND CMRR

Differential Offset2 50 200 50 500 µV

vs. Temperature −40°C ≤ TA ≤ +125°C 900 900 µV Average TC −40°C ≤ TA ≤ +125°C 1 4 1 4 µV/°C

vs. Power Supply (PSRR) VS = ±2.5 V to ±9 V 90 90 dB Common-Mode Offset2 50 50 µV Common-Mode Rejection

Ratio

INPUT CHARACTERISTICS

Input Voltage Range3 Differential input −VS + 0.05 +VS − 0.05 −VS + 0.05 +VS − 0.05 V Single-ended input 2(−VS + 0.05) 2(+V − 0.05) 2(−VS + 0.05) Impedance4 Vcm = VS/2

Single-Ended Input 13.3 13.3 kΩ

Differential Input 20 20 kΩ

Common-Mode Input 10 10 kΩ

OUTPUT CHARACTERISTICS

Output Swing VS = +5 V −VS + 0.125 +VS − 0.14 −VS + 0.125 +VS − 0.14 VS = ±5 V −VS + 0.155 +VS − 0.18 −VS + 0.155 +VS − 0.18 Output Balance Error ∆V Output Impedance 0.1 0.1 Ω Capacitive Load Per output 20 20 pF Short-Circuit Current Limit 35 35 mA

VOCM CHARACTERISTICS

VOCM Input Voltage Range −VS + 1 +VS − 1 −VS + 1 +VS − 1 V VOCM Input Impedance 500 500 kΩ VOCM Gain Error 0.05 0.05 %

22 kHz filter

V

OUT

= V

+OUT

− V

, RL = 2 kΩ differential, referred to output (RTO), TA = 25°C, unless

−OUT

B Grade A Grade

= 200 mV p-p 5 5 MHz

OUT

= 2 V p-p 1 1 MHz

OUT

= 2 V step 10 10 V/µs

OUT

= 2 V step 1.0 1.0 µs

OUT

= 2 V step 1.6 1.6 µs

OUT

= 2 V p-p,

OUT

= 2 V p-p −120 −120 dB

OUT

= 2 V p-p −122 −122 dB

OUT

−102 −102 dB

−82 −82 dBc

= 2 V p-p

OUT

= 4 V p-p 5 5 ppm

OUT

= ±5 V 90 80 dB

IN,cm

2(+VS − 0.05)

/∆V

OUT,cm

90 80 dB

OUT,dm

Unit Min Typ Max Min Typ Max

V

Rev. A | Page 3 of 20

AD8476 Data Sheet

B Grade A Grade

Parameter Test Conditions/Comments

POWER SUPPLY

Specified Supply Voltage ±5 ±5 V Operating Supply Voltage

3 18 3 18 V

Range Supply Current VS = +5 V, TA = 25°C 300 330 300 330 μA VS = ±5 V, TA = 25°C 330 380 330 380 μA

Over Temperature −40°C ≤ TA ≤ +125°C 400 500 400 500 μA

TEMPERATURE RANGE

Specified Performance Range −40 +125 −40 +125 °C

1

Includes amplifier voltage and current noise, as well as noise of internal resistors.

2

Includes input bias and offset current errors.

3

The input voltage range is a function of the voltage supplies and ESD dio des.

4

Internal resistors are trimmed to be r atio matched but have ±20% absolute accuracy.

Unit Min Typ Max Min Typ Max

Rev. A | Page 4 of 20

Data Sheet AD8476

ABSOLUTE MAXIMUM RATINGS

Table 2.

Parameter Rating

Supply Voltage ±10 V

Maximum Voltage at Any Input Pin +VS + 18 V

Minimum Voltage at Any Input Pin −VS – 18 V

Storage Temperature Range −65°C to +150°C

Specified Temperature Range −40°C to +125°C

Package Glass Transition Temperature (TG) 150°C

ESD (Human Body Model) 2500 V

Stresses above those listed under Absolute Maximum Ratings

may cause permanent damage to the device. This is a stress

rating only; functional operation of the device at these or any

other conditions above those indicated in the operational

section of this specification is not implied. Exposure to absolute

maximum rating conditions for extended periods may affect

device reliability.

THERMAL RESISTANCE

The θJA values in Table 3 assume a 4-layer JEDEC standard board with zero airflow.

Table 3. Thermal Resistance

Package Type θJA Unit

8-Lead MSOP 209.0 °C/W

MAXIMUM POWER DISSIPATION

The maximum safe power dissipation for the AD8476 is limited by the associated rise in junction temperature (T approximately 150°C, which is the glass transition temperature, the properties of the plastic change. Even temporarily exceeding this temperature limit may change the stresses that the package exerts on the die, permanently shifting the parametric performance of the amplifiers. Exceeding a temperature of 150°C for an extended period may result in a loss of functionality.

) on the die. At

J

ESD CAUTION

Rev. A | Page 5 of 20

AD8476 Data Sheet

INN

1

+V

S

2

VOCM

3

+OUT

4

INP

8

–V

S

7

NC

6

–OUT

5

AD8476

TOP VIEW

(Not to S cale)

NOTES

1. NC = NO CONNECT. DO NOT CO NNE CT TO THIS PIN.

10195-004

PIN CONFIGURATION AND FUNCTION DESCRIPTIONS

Figure 2. 8-Lead MSOP Pin Configuration

Table 4. 8-Lead MSOP Pin Function Descriptions

Pin No. Mnemonic Description

1 INN Negative Input . 2 +VS Positive Supply. 3 VOCM Output Common-Mode Adjust. 4 +OUT Noninverting Output. 5 −OUT Inverting Output. 6 NC No Connect. 7 −VS Negative Supply. 8 INP Positive Input.

Rev. A | Page 6 of 20