ANALOG DEVICES AD8475 Service Manual

Precision, Selectable Gain,

FEATURES

Precision attenuation: G = 0.4, G = 0.8 Fully differential or single-ended input/output Differential output designed to drive precision ADCs

Drives switched capacitor and Σ-Δ ADCs

Rail-to-rail output VOCM pin adjusts output common mode Robust overvoltage protection up to ±15 V (V Single supply: 3 V to 10 V Dual supplies: ±1.5 V to ±5 V High performance

Suited for driving 18-bit converter up to 4 MSPS

10 nV/√Hz output noise

3 ppm/°C gain drift

500 μV maximum output offset

50 V/μs slew rate Low power: 3.2 mA supply current

APPLICATIONS

ADC drivers Differential instrumentation amplifier building blocks Single-ended-to-differential converters

GENERAL DESCRIPTION

The AD8475 is a fully differential, attenuating amplifier with integrated precision gain resistors. It provides precision attenuation (by 0.4 or 0.8), common-mode level shifting, and single-ended-todifferential conversion along with input overvoltage protection. Power dissipation on a single 5 V supply is only 16 mW.

The AD8475 is a simple to use, fully integrated precision gain block, designed to process signal levels of up to ±10 V on a single supply. It provides a complete interface to make industrial level signals directly compatible with the differential input ranges of low voltage high performance 16-bit or 18-bit single-supply successive approximation (SAR) analog-to-digital converters (ADCs).

The AD8475 comes with two standard pin-selectable gain options: 0.4 and 0.8. The gain of the part is set by driving the input pin corresponding to the appropriate gain.

The AD8475 also provides overvoltage protection from large industrial input voltages up to ±15 V while operating on a single 5 V supply. The VOCM pin adjusts the output voltage common mode for precision level shifting, to match the ADC’s input range and maximize dynamic range.

Rev. B

Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Anal og Devices for its use, nor for any infringements of patents or ot her rights of third parties that may result from its use. Specifications subject to change without notice. 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.

= +5 V)

S

Fully Differential Funnel Amplifier

AD8475

FUNCTIONAL BLOCK DIAGRAMS

S

–V

+IN 0.4x

16

+IN 0.4x

1

1.25kΩ

+IN 0.8x

2

–IN 0.8x

3

–IN 0.4x

NC = NO CONNECT

1.25kΩ

4

5

N 0.4x –I

Figure 1. 16-Lead LFCSP

+IN 0.8x10+IN 0.4x9–V

1.25kΩ

–IN 0.8x1–IN 0.4x

NC = NO CONNECT

Figure 2. 10-Lead MSOP

The AD8475 works extremely well with SAR, Σ-, 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 in the market, the AD8475 is a high precision amplifier. With 500 µV maximum output offset, 10 nV/√Hz output noise, and −112 dB THD + N, the AD8475 pairs well with high accuracy converters. Considering its low power consumption and high precision, the slew-enhanced AD8475 has excellent speed, settling to 18-bit precision for 4 MSPS acquisition.

The AD8475 is available in a space-saving 16-lead 3 mm × 3 mm LFCSP package and a 10-lead MSOP package. It is fully specified over the −40°C to +85°C temperature range.

15

1.25kΩ

6

S

+V

2

14

7

+V

S

8

AD8475

3

S

+V

1kΩ

AD8475

1kΩ

S

NC7–OUT

1kΩ

4

VOCM

13

12

NC

11

–OUT

10

+OUT

9

VOCM

8

S

+V

09432-001

6

5

+OUT

09432-002

AD8475

REVISION HISTORY

4/11—Rev. A to Rev. B

Added B Grade Columns to Specifications Section..................... 3

Changes to Figure 16........................................................................ 9

Changes to Figure 43...................................................................... 14

Changes to Ordering Guide.......................................................... 24

1/11—Rev. 0 to Rev. A

Added 16-Lead LFCSP.................................................. Throughout

Changes to Table 1 and Note 3........................................................ 3

Change to Table 2............................................................................. 5

Added Figure 3 and Table 4; Renumbered Sequentially ............. 6

Changes to Typical Performance Characteristics Format........... 8

Added AD8475 Evaluation Board Section and Figure 56......... 22

10/10—Revision 0: Initial Version

Rev. B | Page 2 of 24

AD8475

SPECIFICATIONS

VS = 5 V, G = 0.4, VOCM connected to 2.5 V, RL = 1 kΩ differentially, TA = 25°C, referred to output (RTO), unless otherwise noted.

Table 1.

B Grade A Grade

Parameter Test Conditions/Comments Min Typ Max Min Typ Max Unit

DYNAMIC PERFORMANCE

−3 dB Small Signal Bandwidth

−3 dB Large Signal Bandwidth

Slew Rate 2 V step 50 50 V/μs Settling Time to 0.01% 2 V step on output 45 45 ns Settling Time to 0.001% 2 V step on output 50 50 ns

NOISE/DISTORTION1

THD + N

HD2 f = 1 MHz, V HD3 f = 1 MHz, V IMD3

IMD3

Output Voltage Noise f = 0.1 Hz to 10 Hz 2.5 2.5 μV p-p Spectral Noise Density f = 1 kHz 10 10 nV/√Hz

GAIN 0.4 0.4 V/V

Gain Error RL = ∞ 0.02 0.05 % Gain Drift −40°C ≤ TA ≤ +85°C 1 3 1 3 ppm/°C Gain Nonlinearity V

OFFSET AND CMRR

Offset2 RTO 50 200 50 500 μV

vs. Temperature −40°C ≤ TA ≤ +85°C 2.5 2.5 μV/°C vs. Power Supply VS = ±2.5 V to ±5 V 90 90 dB

Common-Mode Rejection

Ratio

INPUT CHARACTERISTICS

Input Voltage Range3 Differential input −6.25 +6.25 −6.25 +6.25 V Single-ended input −12.5 +12.5 −12.5 +12.5 V Impedance4 V

Single-Ended Input 2.92 2.92 kΩ Differential Input 5 5 kΩ Common Mode Input 1.75 1.75 kΩ

OUTPUT CHARACTERISTICS

Output Swing

Output Balance Error ∆V Output Impedance 0.1 0.1 Ω Capacitive Load Per output 30 30 pF Short-Circuit Current Limit 110 110 mA

VOCM CHARACTERISTICS

VOCM Input Voltage Range −VS + 1 +VS −VS + 1 +VS V VOCM Input Impedance 100 100 kΩ VOCM Gain Error 0.02 0.02 %

150 150 MHz

15 15 MHz

f = 100 kHz, V

= 4 V p-p,

OUT

−112 −112 dB

22 kHz band-pass filter

= 2 V p-p −110 −110 dB

OUT

= 2 V p-p −96 −96 dB

OUT

= 0.95 MHz, f2 = 1.05 MHz,

f

1

= 2 V p-p

V

OUT

= 95 kHz, f2 = 105 kHz,

f

1

V

= 2 V p-p

OUT

= 4 V p-p 2.5 2.5 ppm

OUT

V

= ±5 V 86 76 dB

INcm

= VS/2

INcm

OUT,cm

/∆V

90 −80 dB

OUT,dm

−90 −90 dBc

−84 −84 dBc

−V

0.05

+

S

+V

0.05

−

S

−VS +

0.05

+V

S

−

0.05

Rev. B | Page 3 of 24

AD8475

B Grade A Grade

Parameter Test Conditions/Comments Min Typ Max Min Typ Max Unit

POWER SUPPLY

Specified Voltage 5 5 V Operating Voltage Range 3 10 3 10 V Supply Current 3 3.2 3 3.2 mA

Over Temperature −40°C ≤ TA ≤ +85°C 4 4 mA

TEMPERATURE RANGE

Specified Performance Range −40 +85 −40 +85 °C Operating 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 diodes.

4

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

Rev. B | Page 4 of 24

AD8475

ABSOLUTE MAXIMUM RATINGS

Table 2.

Parameter Rating

Supply Voltage 11 V Maximum Voltage at Any Input Pin +VS + 10.5 V Minimum Voltage at Any Input Pin −VS − 16 V Storage Temperature Range −65°C to +150°C Specified Temperature Range −40°C to +85°C Operating Temperature Range −40°C to +125°C Junction Temperature 150°C ESD (FICDM) 1500 V ESD (HBM) 2000 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

θJA is specified for the worst-case conditions, that is, a device soldered in a circuit board for surface-mount packages.

Table 3. Thermal Resistance

Package Type θJA Unit

16-Lead LFCSP (Exposed Pad) 84.90 °C/W 10-Lead MSOP 214.0 °C/W

ESD CAUTION

Rev. B | Page 5 of 24

AD8475

x

PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS

S

–V

+IN 0.4

16

15

14

13

+IN 0.4x

1

2

3

4

AD8475

TOP VIEW

(Not to Scale

6

5

7

S

+V

–IN 0.4x

+IN 0.8x

–IN 0.8x

–IN 0.4x

NOTES

1. NC = NO CONNECT.

2. SOLDER THE EXPOSED PADDLE ON T HE BACK OF THE PACKAG E TO A GRO UND PLANE.

Figure 3. 16-Lead LFCSP Pin Configuration

Table 4. 16-Lead LFCSP Pin Function Descriptions

Pin No. Mnemonic Description

1 +IN 0.4x Positive Input for 0.4 Attenuation. 2 +IN 0.8x Positive Input for 0.8 Attenuation 3 −IN 0.8x Negative Input for 0.8 Attenuation. 4 −IN 0.4x Negative Input for 0.4 Attenuation. 5 −IN 0.4x Negative Input for 0.4 Attenuation. 6 +VS Positive Supply. 7 +VS Positive Supply. 8 +VS Positive Supply. 9 VOCM Output Common-Mode Adjust. 10 +OUT Positive Output. 11 −OUT Negative Output. 12 NC No Connect. 13 −VS Negative Supply. 14 −VS Negative Supply. 15 −VS Negative Supply. 16 +IN 0.4x Positive Input for 0.4 Attenuation. EPAD Solder the exposed paddle on the back of the package to a ground plane.

NC

12

–OUT

11

10

+OUT

9

VOCM

8

S

+V

09432-003

Rev. B | Page 6 of 24

AD8475

–IN 0.8x

–IN 0.4x

+V

VOCM

S

1

2

3

4

AD8475

TOP VIEW

(Not to Scale

10

9

8

7

+IN 0.8x

+IN 0.4x

–V

S

NC

5

+OUT

NC = NO CONNECT

Figure 4. 10-Lead MSOP Pin Configuration

Table 5. 10-Lead MSOP Pin Function Descriptions

Pin No. Mnemonic Description

1 −IN 0.8x Negative Input for 0.8 Attenuation 2 −IN 0.4x Negative Input for 0.4 Attenuation 3 +VS Positive Supply 4 VOCM Output Common-Mode Adjust 5 +OUT Noninverting Output 6 −OUT Inverting Output 7 NC No Connect 8 −VS Negative Supply 9 +IN 0.4x Positive Input for 0.4 Attenuation 10 +IN 0.8x Positive Input for 0.8 Attenuation

6

–OUT

09432-004

Rev. B | Page 7 of 24

AD8475

TYPICAL PERFORMANCE CHARACTERISTICS

TA = 25°C, VS = 5 V, gain = 0.4, R

1000

REPRESENTATIVE SAMPLES

800

600

400

200

(µV)

0

OSO

V

–200

–400

–600

–800

–1000

–40 120100806040200–20

Figure 5. System Offset vs. Temperature

5

REPRESENTATIVE SAMPLES

4

3

2

1

0

–1

CMRR (µV/V)

–2

–3

–4

–5

–40 120100806040200–20

Figure 6. CMRR vs. Temperature (G = 0.8)

65

60

55

50

45

FALL

SLEW RATE (V/µs)

40

35

30

–40 120

RISE

Figure 7. Slew Rate vs. Temperature

TEMPERATURE (°C)

TEMPERAT URE (°C)

= 1 kΩ, RTO, unless otherwise specified.

LOAD

G = 0.8

G = 0.4

09432-006

09432-005

100806040200–20

09432-015

10

8

6

4

2

0

–2

–4

COMMON-MODE VOLTAGE (V)

–6

–4.97V, –6. 25V

–8

–5.5 –4.5 –3.5 –2.5 –1.5 –0.5 0. 5 1.5 2. 5 3.5 4.5 5.5

VS = +5V, VOCM = +2.5V

VS = +3V, VOCM = +1.5V

–2.97V, –3.75V

OUTPUT VO LTAGE (V)

0V, +7.75V–4.97V, +7. 75V +4.95V, + 7.75V

0V, +3.25V–2.97V, +3 .25V

0V, –3.75V +2.95V, –3. 75V

0V, –6.25V

+2.95V, + 3.25V

+4.95V, –6. 25V

Figure 8. Input Common-Mode Voltage vs. Output Voltage,

= +5 V and +3 V

V

S

150

VIN = ±5V REPRESENTATIVE SAMPLES

100

50

0

–50

GAIN ERRO R (µV/V)

–100

–150

–40 120100806040200–20

Figure 9. Gain Error vs. Temperature, V

TEMPERAT URE (°C)

= ±5 V

S

130

125

120

115

110

105

100

95

90

SHORT-CIRCUIT CURRENT (mA)

85

80

–40 120100806040200–20

TEMPERATURE (°C)

Figure 10. Short-Circuit Current vs. Temperature

09432-008

09432-100

09432-016

Rev. B | Page 8 of 24

ANALOG DEVICES AD8475 Service Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

FEATURES

APPLICATIONS

GENERAL DESCRIPTION

FUNCTIONAL BLOCK DIAGRAMS

TABLE OF CONTENTS

REVISION HISTORY

SPECIFICATIONS

ABSOLUTE MAXIMUM RATINGS

THERMAL RESISTANCE

ESD CAUTION

PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS

TYPICAL PERFORMANCE CHARACTERISTICS