Datasheet

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Low Noise,

Precision CMOS Amplifier

Data Sheet

AD8655/AD8656

Rev. D Document Feedback

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FEATURES

Low noise: 2.7 nV/√Hz @ f = 10 kHz

Low offset voltage: 250 µV max over V

Offset voltage drift: 0.4 µV/°C typ and 2.3 µV/°C max

Bandwidth: 28 MHz

Rail-to-rail input/output

Unity gain stable

2.7 V to 5.5 V operation

−40°C to +125°C operation

Qualified for automotive applications (AD8656)

APPLICATIONS

ADC and DAC buffers

Audio

Industrial controls

Precision filters

Digital scales

Automotive collision avoidance

PLL filters

PIN CONFIGURATIONS

–IN

+IN

V–

V+

OUT

AD8655

TOP VIEW

(Not to Scale)

05304-048

NC = NO CONNECT

OUT A

–IN A

+IN A

–

V+

OUT B

–IN B

+IN B

AD8656

TOP VIEW

(Not to Scale)

05304-059

Figure 1. AD8655

8-Lead MSOP (RM-8)

Figure 2. AD8656

8-Lead MSOP (RM-8)

–IN

+IN

V–

V+

OUT

NC = NO CONNECT

AD8655

TOP VIEW

(Not to Scale)

05304-049

OUT A

–IN A

+IN A

V–

V+

OUT B

–

IN B

+IN B

AD8656

TOP VIEW

(Not to Scale)

05304-060

Figure 3. AD8655

8-Lead SOIC (R-8)

Figure 4. AD8656

8-Lead SOIC (R-8)

GENERAL DESCRIPTION

The AD8655/AD8656 are the industry’s lowest noise, precision

CMOS amplifiers. They leverage the Analog Devices DigiTrim®

technology to achieve high dc accuracy.

The AD8655/AD8656 provide low noise (2.7 nV/√Hz @ 10 kHz),

low THD + N (0.0007%), and high precision performance

(250 µV max over V

) to low voltage applications. The ability

to swing rail-to-rail at the input and output enables designers

to buffer analog-to-digital converters (ADCs) and other wide

dynamic range devices in single-supply systems.

The high precision performance of the AD8655/AD8656

improves the resolution and dynamic range in low voltage

applications. Audio applications, such as microphone pre-amps

and audio mixing consoles, benefit from the low noise, low

distortion, and high output current capability of the AD8655/

AD8656 to reduce system level noise performance and maintain

audio fidelity. The high precision and rail-to-rail input and

output of the AD8655/AD8656 benefit data acquisition, process

controls, and PLL filter applications.

The AD8655/AD8656 are fully specified over the −40°C to

+125°C temperature range. The AD8655/AD8656 are available

in Pb-free, 8-lead MSOP and SOIC packages.

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Summary of content (20 pages)

PAGE 1
Low Noise, Precision CMOS Amplifier AD8655/AD8656 Data Sheet AD8655 +IN 3 TOP VIEW (Not to Scale) V– 4 NC OUT A 1 7 V+ –IN A 2 6 OUT +IN A 3 5 NC NC = NO CONNECT NC 1 +IN 3 AD8655 TOP VIEW V– 4 (Not to Scale) V– 4 8 NC OUT A 1 7 V+ –IN A 2 6 OUT +IN A 3 5 NC NC = NO CONNECT Figure 3. AD8655 8-Lead SOIC (R-8) AD8656 TOP VIEW (Not to Scale) 8 V+ 7 OUT B 6 –IN B 5 +IN B Figure 2. AD8656 8-Lead MSOP (RM-8) Figure 1.
PAGE 2
AD8655/AD8656 Data Sheet TABLE OF CONTENTS Specifications..................................................................................... 3 Driving Capacitive Loads .......................................................... 16 Absolute Maximum Ratings ............................................................ 5 Layout, Grounding, and Bypassing Considerations .................. 18 ESD Caution ..................................................................................
PAGE 3
AD8655/AD8656 Data Sheet SPECIFICATIONS VS = 5.0 V, VCM = VS/2, TA = 25°C, unless otherwise specified. Table 1. Parameter INPUT CHARACTERISTICS Offset Voltage Symbol Conditions VOS VCM = 0 V to 5 V −40°C ≤ TA ≤ +125°C −40°C ≤ TA ≤ +125°C Offset Voltage Drift Input Bias Current ∆VOS/∆T IB Input Offset Current IOS Min Typ Max Unit 50 250 550 2.3 10 500 10 500 5 µV µV µV/°C pA pA pA pA V dB dB dB 0.
PAGE 4
AD8655/AD8656 Data Sheet VS = 2.7 V, VCM = VS/2, TA = 25°C, unless otherwise specified. Table 2. Parameter INPUT CHARACTERISTICS Offset Voltage Symbol Conditions VOS VCM = 0 V to 2.7 V −40°C ≤ TA ≤ +125°C −40°C ≤ TA ≤ +125°C Offset Voltage Drift Input Bias Current ∆VOS/∆T IB Input Offset Current IOS Min Typ Max Unit 44 250 550 2.0 10 500 10 500 2.7 µV µV µV/°C pA pA pA pA V dB dB dB 0.
PAGE 5
AD8655/AD8656 Data Sheet ABSOLUTE MAXIMUM RATINGS Table 3. Parameter Supply Voltage Input Voltage Differential Input Voltage Output Short-Circuit Duration to GND Electrostatic Discharge (HBM) Storage Temperature Range R, RM Packages Junction Temperature Range R, RM Packages Lead Temperature (Soldering, 10 sec) Rating 6V VSS − 0.3 V to VDD + 0.3 V ±6 V Indefinite 3.
PAGE 6
AD8655/AD8656 Data Sheet TYPICAL PERFORMANCE CHARACTERISTICS 60 20 VS = ±2.5V VS = ±2.5V 10 40 VOS (µV) 30 20 10 0 –10 05304-001 –20 0 –150 –50 –100 50 0 VOS (µV) –30 150 100 05304-004 NUMBER OF AMPLIFIERS 50 0 Figure 5. Input Offset Voltage Distribution 1 2 3 4 COMMON-MODE VOLTAGE (V) 5 6 Figure 8. Input Offset Voltage vs. Common-Mode Voltage 150.0 250 VS = ±2.5V VS = ±2.5V 100.0 200 50.0 IB (pA) VOS (µV) 150 0.0 100 –50.0 05304-002 –150.
PAGE 7
AD8655/AD8656 Data Sheet 4.5 4.996 VS = ±2.5V VS = ±2.5V LOAD CURRENT = 1mA 4.994 4.992 3.5 VOH (V) SUPPLY CURRENT (mA) 4.0 3.0 4.990 4.988 4.986 2.5 2.0 –50 0 50 TEMPERATURE (°C) 100 4.982 –50 150 Figure 11. Supply Current vs. Temperature 0 50 TEMPERATURE (°C) 100 12 LOAD CURRENT = 1mA VS = ±2.5V VS = ±2.5V 10 1500 8 VOL (mV) 2000 VOH 1000 6 VOL 500 0 50 100 150 CURRENT LOAD (mA) 200 05304-010 05304-008 4 0 2 –50 250 0 50 TEMPERATURE (°C) 100 150 Figure 15.
PAGE 8
AD8655/AD8656 Data Sheet 100 110.00 VS = ±2.5V VCM = 0V CMRR (dB) 104.00 101.00 98.00 05304-012 95.00 92.00 –50 0 50 TEMPERATURE (°C) 100 10 05304-019 VOLTAGE NOISE DENSITY (nV/√Hz 1/2) VS = ±2.5V 107.00 1 1 150 10 100 1k FREQUENCY (Hz) 10k 100k Figure 20. Voltage Noise Density vs. Frequency Figure 17. Large Signal CMRR vs. Temperature 100 +PSRR –PSRR VS = ±2.5V Vn (p-p) = 1.23µV 60 500nV/DIV PSRR (dB) 80 VS = ±2.
PAGE 9
AD8655/AD8656 Data Sheet –45 120 6 100 5 PHASE MARGIN = 69° PHASE SHIFT (Degrees) –90 60 40 –135 20 –180 0 4 OUTPUT (V) 80 GAIN (dB) VS = ±2.5V VIN = 5V G = +1 VS = ±2.5V CLOAD = 11.5pF 3 2 1 100k 1M FREQUENCY (Hz) –225 100M 10M 05304-018 –40 10k 05304-015 –20 0 10k 100k 1M FREQUENCY (Hz) 10M Figure 26. Maximum Output Swing vs. Frequency Figure 23. Open-Loop Gain and Phase vs. Frequency 140.00 VS = ±2.5V RL = 10kΩ 130.00 120.00 VOUT (1V/DIV) AVO (dB) T VS = ±2.
PAGE 10
AD8655/AD8656 Data Sheet 30 100 OUTPUT IMPEDANCE (Ω) 25 OVERSHOOT % VS = ±2.5V VS = ±2.5V VIN = 200mV 20 –OS 15 10 +OS G = +100 G = +1 G = +10 10 1 0 0 50 100 150 200 250 CAPACITANCE (pF) 300 0.1 100 350 Figure 29. Small Signal Overshoot vs. Load Capacitance 05304-027 05304-024 5 1k 10k 100k FREQUENCY (Hz) 1M 10M 100M Figure 32. Output Impedance vs. Frequency 80 VS = ±1.35V T 70 300mV NUMBER OF AMPLIFIERS VIN 0V 1 0V 2 VS = ±2.
PAGE 11
AD8655/AD8656 Data Sheet 80 10000 VS = ±1.35V VS = ±1.35V 50 40 30 20 05304-030 10 0 0 0.2 0.4 0.6 0.8 1.0 1.2 |TCVOS| (µV/°C) 1.4 1000 100 VOL 10 05304-057 60 DELTA OUTPUT FROM SUPPLY (mV) NUMBER OF AMPLIFIERS 70 VOH 1 0.1 1.6 Figure 35. |TCVOS| Distribution 1 10 CURRENT LOAD (mA) 100 Figure 38. AD8656 Output Swing vs. Current Load 4.5 2.698 VS = ±1.35V 2.694 2.690 3.5 VOH (V) 2.686 3.0 2.682 2.5 05304-031 2.678 2.0 –50 0 50 TEMPERATURE (°C) 100 2.
PAGE 12
AD8655/AD8656 Data Sheet 35 T VS = ±1.35V G = +1 CL = 50pF VIN VS = ±1.35V VIN = 200mV 30 –OS OVERSHOOT % 25 1V/DIV VOUT 2 20 15 +OS 10 05304-044 05304-047 5 0 0 20µs/DIV 150 200 250 CAPACITANCE (pF) 300 350 Figure 44. Small Signal Overshoot vs. Load Capacitance Figure 41. No Phase Reversal T T VS = ±1.35V CL = 50pF GAIN = +1 100 50 200mV VIN 2 0V 2 VOUT –1.35V 05304-042 VS = ±1.35V VIN = 200mV GAIN = –10 RECOVERY TIME = 180ns 400ns/DIV TIME (10µs/DIV) Figure 42.
PAGE 13
AD8655/AD8656 Data Sheet 120 120 VS = ±1.35V VIN = 28mV RL = 1MΩ CL = 47pF 100 PHASE MARGIN = 54° 80 60 GAIN (dB) CMRR (dB) –90 80 PHASE SHIFT (Degrees) 100 –45 VS = ±1.35V CLOAD = 11.5pF 60 40 –135 20 40 –180 0 20 0 100 1k 10k FREQUENCY (Hz) 100k –40 10k 1M 100k 1M FREQUENCY (Hz) 05304-036 05304-034 –20 –225 100M 10M Figure 50. Open-Loop Gain and Phase vs. Frequency Figure 47. CMRR vs. Frequency 130.00 102.00 VS = ±1.35V RL = 10kΩ VS = ±1.35V 120.
PAGE 14
AD8655/AD8656 3.0 0 2.5 –20 1.5 1.0 0.5 100k 1M FREQUENCY (Hz) G = +100 G = +10 G = +1 1 05304-041 OUTPUT IMPEDANCE (Ω) 100 10k 100k 1M FREQUENCY (Hz) 10M 100M Figure 54. Output Impedance vs. Frequency Rev. D | Page 14 of 20 Downloaded from Arrow.com. V– VOUT B V+ –60 –80 –100 100 1k 10k 100k FREQUENCY (Hz) 1M 10M Figure 55. Channel Separation vs. Frequency VS = ±1.35V 1k A –2.5V 10 1000 0.1 100 –40 + – –140 10M Figure 53. Maximum Output Swing vs.
PAGE 15
AD8655/AD8656 Data Sheet THEORY OF OPERATION The AD8655/AD8656 amplifiers are voltage feedback, rail-torail input and output precision CMOS amplifiers, which operate from 2.7 V to 5.0 V of power supply voltage. These amplifiers use the Analog Devices DigiTrim technology to achieve a higher degree of precision than is available from most CMOS amplifiers. DigiTrim technology, used in a number of ADI amplifiers, is a method of trimming the offset voltage of the amplifier after it is packaged.
PAGE 16
AD8655/AD8656 Data Sheet APPLICATIONS INPUT OVERVOLTAGE PROTECTION The internal protective circuitry of the AD8655/AD8656 allows voltages exceeding the supply to be applied at the input. It is recommended, however, not to apply voltages that exceed the supplies by more than 0.3 V at either input of the amplifier. If a higher input voltage is applied, series resistors should be used to limit the current flowing into the inputs. The input current should be limited to less than 5 mA.
PAGE 17
AD8655/AD8656 Data Sheet 1.0 THD Readings vs. Common-Mode Voltage 0.5 Total harmonic distortion of the AD8655/AD8656 is well below 0.0007% with a load of 1 kΩ. This distortion is a function of the circuit configuration, the voltage applied, and the layout, in addition to other factors. 0.2 0.1 % 0.02 0.01 0.005 0.002 VOUT AD8655 0.001 RL SWEEP 1 0.0002 0.0001 Figure 59. THD + N Test Circuit 05304-055 –2.5V SWEEP 2 0.0005 05304-054 VIN SWEEP 2: VIN = 2V p-p RL = 1kW 0.05 +2.
PAGE 18
AD8655/AD8656 Data Sheet LAYOUT, GROUNDING, AND BYPASSING CONSIDERATIONS POWER SUPPLY BYPASSING LEAKAGE CURRENTS Power supply pins can act as inputs for noise, so care must be taken to apply a noise-free, stable dc voltage. The purpose of bypass capacitors is to create low impedances from the supply to ground at all frequencies, thereby shunting or filtering most of the noise.
PAGE 19
AD8655/AD8656 Data Sheet OUTLINE DIMENSIONS 5.00 (0.1968) 4.80 (0.1890) 5 4 1.27 (0.0500) BSC 0.25 (0.0098) 0.10 (0.0040) COPLANARITY 0.10 SEATING PLANE 6.20 (0.2441) 5.80 (0.2284) 1.75 (0.0688) 1.35 (0.0532) 0.51 (0.0201) 0.31 (0.0122) 8 3.20 3.00 2.80 0.50 (0.0196) 0.25 (0.0099) 45° 5.15 4.90 4.65 4 PIN 1 IDENTIFIER 8° 0° 0.25 (0.0098) 0.17 (0.0067) 1 5 0.65 BSC 1.27 (0.0500) 0.40 (0.
PAGE 20
AD8655/AD8656 Data Sheet NOTES ©2005–2013 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D05304-0-6/13(D) Rev. D | Page 20 of 20 Downloaded from Arrow.com.