Datasheet

ManualsBrandsANALOG DEVICES ManualsLinear ICsLinear IC - In-amp InAmp MSOP 8

40 μA Micropower Instrumentation

Amplifier with Zero Crossover Distortion

AD8236

Rev. 0

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 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.

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.

Tel: 781.329.4700 www.analog.com

FEATURES

Low power: 40 μA supply current (maximum)

Low input currents

1 pA input bias current

0.5 pA input offset current

High CMRR: 110 dB CMRR, G = 100

Space-saving MSOP

Zero input crossover distortion

Rail-to-rail input and output

Gain set with single resistor

Operates from 1.8 V to 5.5 V

APPLICATIONS

Medical instrumentation

Low-side current sense

Portable devices

CONNECTION DIAGRAM

–IN

+IN

OUT

REF

–V

AD8236

TOP VIEW

(Not to Scale)

08000-001

Figure 1.

1.0

2.0

4.0

3.0

5.0

0.5

1.5

3.5

2.5

4.5

OUTPUT VOLTAGE (V)

INPUT COMMON-MODE VOLTAGE (V)

08000-002

5.55.00.5–0.5 1.5 2.0 3.0 4.0 4.50 1.0 2.5 3.5

G = 5

= 5V

REF

= 2.5V

G = 5

= 1.8V

REF

= 0.9V

Figure 2. Wide Common-Mode Voltage Range vs. Output Voltage

GENERAL DESCRIPTION

The AD8236 is the lowest power instrumentation amplifier

in the industry. It has rail-to-rail outputs and can operate on

voltages as low as 1.8 V. Its 40 µA maximum supply current

makes it an excellent choice in battery-powered applications.

The AD8236’s high input impedance, low input bias current of

1 pA, high CMRR of 110 dB (G = 100), small size, and low power

offer tremendous value. It has a wider common-mode voltage

range than typical three-op-amp instrumentation amplifiers,

making this a great solution for applications that operate on a

single 1.8 V or 3 V supply. An innovative input stage allows for

a wide rail-to-rail input voltage range without the crossover

distortion common in other designs.

The AD8236 is available in an 8-lead MSOP and is specified

over the industrial temperature range of −40°C to +125°C.

Table 1. Instrumentation Amplifiers by Category

General

Purpose Zero Drift

Military

Grade

Low

Power

High Speed

PGA

AD8220 AD8230 AD620 AD8236 AD8250

AD8221 AD8231 AD621 AD627 AD8251

AD8222 AD8290 AD624 AD623 AD8253

AD8228 AD8293G80 AD524 AD8223

AD8295 AD8293G160 AD526 AD8226

AD8553

AD8556

AD8557

See www.analog.com/inamps for the latest instrumentation amplifiers.

Summary of content (20 pages)

PAGE 1
40 μA Micropower Instrumentation Amplifier with Zero Crossover Distortion AD8236 FEATURES CONNECTION DIAGRAM Low power: 40 μA supply current (maximum) Low input currents 1 pA input bias current 0.5 pA input offset current High CMRR: 110 dB CMRR, G = 100 Space-saving MSOP Zero input crossover distortion Rail-to-rail input and output Gain set with single resistor Operates from 1.8 V to 5.5 V –IN 1 8 +VS RG 2 7 VOUT RG 3 6 REF +IN 4 5 –VS 08000-001 AD8236 TOP VIEW (Not to Scale) Figure 1.
PAGE 2
AD8236 TABLE OF CONTENTS Features .............................................................................................. 1 Layout .......................................................................................... 15 Applications ....................................................................................... 1 Reference Terminal .................................................................... 15 Connection Diagram ...............................................................
PAGE 3
AD8236 SPECIFICATIONS +VS = 5 V, −VS = 0 V (GND), VREF = 2.5 V, TA = 25°C, G = 5, RL = 100 kΩ to GND, unless otherwise noted. Table 2. Parameter COMMON-MODE REJECTION RATIO (CMRR) CMRR DC G=5 G = 10 G = 100 G = 200 NOISE Voltage Noise Spectral Density, RTI RTI, 0.1 Hz to 10 Hz G=5 G = 200 Current Noise VOLTAGE OFFSET Input Offset, VOS Average Temperature Coefficient (TC) Offset RTI vs.
PAGE 4
AD8236 Parameter GAIN Gain Range Gain Error G=5 G = 10 G = 100 G = 200 Nonlinearity G=5 G = 10 G = 100 G = 200 Gain vs. Temperature G=5 G > 10 INPUT Differential Impedance Common-Mode Impedance Input Voltage Range OUTPUT Output Voltage High, VOH Output Voltage Low, VOL Short-Circuit Limit, ISC REFERENCE INPUT RIN IIN Voltage Range Gain to Output POWER SUPPLY Operating Range Quiescent Current Overtemperature TEMPERATURE RANGE For Specified Performance 1 Test Conditions Min G = 5 + 420 kΩ/RG VS = ±2.
PAGE 5
AD8236 +VS = 1.8 V, −VS = 0 V (GND), VREF = 0.9 V, TA = 25°C, G = 5, RL = 100 kΩ to GND, unless otherwise noted. Table 3. Parameter COMMON-MODE REJECTION RATIO (CMRR) CMRR DC G=5 G = 10 G = 100 G = 200 NOISE Voltage Noise Spectral Density, RTI RTI, 0.1 Hz to 10 Hz G=5 G = 200 Current Noise VOLTAGE OFFSET Input Offset, VOS Average Temperature Coefficient (TC) Offset RTI vs.
PAGE 6
AD8236 Parameter Nonlinearity G=5 G = 10 G = 100 G = 200 Gain vs. Temperature G=5 G > 10 INPUT Differential Impedance Common-Mode Impedance Input Voltage Range OUTPUT Output Voltage High, VOH Output Voltage Low, VOL Short-Circuit Limit, ISC REFERENCE INPUT RIN IIN Voltage Range Gain to Output POWER SUPPLY Operating Range Quiescent Current Overtemperature TEMPERATURE RANGE For Specified Performance 1 Test Conditions RL = 10 kΩ or 100 kΩ Min Typ Max Unit 1 1 0.5 0.4 10 10 10 10 ppm ppm ppm ppm 0.
PAGE 7
AD8236 ABSOLUTE MAXIMUM RATINGS Table 4. Rating 6V See Figure 3 55 mA ±VS ±VS −65°C to +125°C −40°C to +125°C 300°C 140°C The difference between the total drive power and the load power is the drive power dissipated in the package. PD = Quiescent Power + (Total Drive Power – Load Power) ⎛V V PD = (VS × I S ) + ⎜⎜ S × OUT RL ⎝ 2 ⎞ VOUT 2 ⎟– ⎟ RL ⎠ RMS output voltages should be considered. If RL is referenced to −VS, as in single-supply operation, the total drive power is VS × IOUT.
PAGE 8
AD8236 –IN 1 RG 2 RG 3 +IN 4 8 AD8236 +VS 7 TOP VIEW (Not to Scale) VOUT 6 REF 5 –VS 08000-004 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS Figure 4. Pin Configuration Table 5. Pin Function Descriptions Pin No.
PAGE 9
AD8236 TYPICAL PERFORMANCE CHARACTERISTICS G = 5, +VS = 5 V, VREF = 2.5 V, RL = 100 kΩ tied to GND, TA = 25°C, unless otherwise noted. GAIN = 5 700 NUMBER OF UNITS 600 500 400 300 100 –40 –20 0 20 1s/DIV 08000-060 5µV/DIV 0 08000-024 200 40 CMRR (µV/V) Figure 8. 0.1 Hz to 10 Hz RTI Voltage Noise Figure 5.
PAGE 10
AD8236 120 15 GAIN = 100 100 10 CMRR (µV/V) 5 60 0 40 –5 20 –10 0.1 1 10 100 1k 10k –15 –40 100k –20 0 FREQUENCY (Hz) Figure 11. Negative PSRR vs. Frequency, RTI, VS = ±0.9 V, ±2.5 V, VREF = 0 V 50 GAIN = 100 30 60 GAIN = 200 GAIN = 100 40 GAIN = 10 20 GAIN (dB) CMRR (dB) 120 GAIN = 200 40 80 10 GAIN = 5 0 –10 GAIN = 10 –20 08000-023 20 GAIN = 5 1 10 100 1k –30 –40 100k 10k 10 100 10k 100k 1M Figure 15. Gain vs. Frequency, VS = 1.8 V, 5 V Figure 12.
PAGE 11
AD8236 08000-026 RLOAD = 10kΩ TIED TO GND VS = 5V 0.5 1.0 1.5 2.0 2.5 3.0 OUTPUT VOLTAGE (V) 3.5 4.0 4.5 (4.98V, 4.737V) (0.01V, 4.24V) 4.0 3.5 3.0 2.5 2.0 1.5 1.0 (4.98V, 0.767V) (0.01V, 0.27V) 0.5 0 –0.5 4.5 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 OUTPUT VOLTAGE (V) Figure 17. Gain Nonlinearity, G = 5 08000-036 RLOAD = 100kΩ TIED TO GND INPUT COMMON-MODE VOLTAGE (V) NONLINEARITY (5ppm/DIV) 5.0 Figure 20. Input Common-Mode Voltage Range vs.
PAGE 12
AD8236 1.6 (1.75V, 1.705V) (0.03V, 1.533V) 1.4 1.2 2V/DIV 1.0 0.8 444μs TO 0.01% 0.6 0.4 (1.75V, 0.275V) 0 –0.2 0 0.2 0.4 08000-047 (0.03V, 0.103V) 0.2 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 OUTPUT VOLTAGE (V) 08000-039 INPUT COMMON-MODE VOLTAGE (V) 1.8 1ms/DIV Figure 26. Large Signal Pulse Response and Settling Time, VS = ±2.5 V, VREF = 0 V, RL = 10 kΩ to VREF Figure 23. Input Common-Mode Voltage Range vs. Output Voltage, G = 200, VS = 1.8 V, VREF = 0.9 V +VS –0.002 –0.
PAGE 13
AD8236 500 20mV/DIV SETTLING TIME (µs) 400 300 200 0 100µs/DIV 0 1 2 08000-043 08000-017 100 4 3 OUTPUT VOLTAGE STEP SIZE (V) Figure 29. Small Signal Pulse Response, G = 5, CL = 100 pF, VS = ±0.9 V, VREF = 0 V, RL = 100 kΩ to VREF Figure 32. Settling Time vs. Output Voltage Step Size, VS = ±2.5 V, VREF = 0 V, RL = 10 kΩ Tied to VREF 40 38 20mV/DIV SUPPLY CURRENT (µA) 36 1.
PAGE 14
AD8236 THEORY OF OPERATION RG ESD PROTECTION ESD PROTECTION REF 6 210kΩ 52.5kΩ RG RG 3 +VS –VS 8 5 ESD PROTECTION 52.5kΩ 210kΩ OP AMP A OP AMP B ESD PROTECTION ESD PROTECTION 1 4 ESD PROTECTION 7 VOUT 08000-006 2 AD8236 +IN –IN Figure 34. Simplified Schematic The AD8236 is a monolithic, 2-op-amp instrumentation amplifier. It was designed for low power, portable applications where size and low quiescent current are paramount.
PAGE 15
AD8236 INCORRECT LAYOUT Careful board layout maximizes system performance. In applications that need to take advantage of the low input bias current of the AD8236, avoid placing metal under the input path to minimize leakage current. CORRECT AD8236 AD8236 REF REF V V Grounding + REFERENCE TERMINAL The reference terminal, REF, is at one end of a 210 kΩ resistor (see Figure 34).
PAGE 16
AD8236 +VS +VS AD8236 AD8236 REF REF –VS –VS TRANSFORMER TRANSFORMER +VS +VS C C 1 fHIGH-PASS = 2πRC AD8236 R AD8236 REF REF R –VS AC-COUPLED 08000-139 –VS AC-COUPLED Figure 38. Creating an IBIAS Path INPUT BIAS CURRENT RETURN PATH RF INTERFERENCE The AD8236 input bias current is extremely small at less than 10 pA. Nonetheless, the input bias current must have a return path to common.
PAGE 17
AD8236 To eliminate high frequency common-mode signals while using smaller source resistors, a low-pass RC network can be placed at the input of the instrumentation amplifier (see Figure 40). The filter limits the input signal bandwidth according to the following relationship: FilterFreqDIFF = FilterFreqCM = 1 2πR(2 CD + CC + CG ) COMMON-MODE INPUT VOLTAGE RANGE The common-mode input voltage range is a function of the input voltages, reference voltage, supplies, and the output of Internal Op Amp A.
PAGE 18
AD8236 APPLICATIONS INFORMATION +VS AC-COUPLED INSTRUMENTATION AMPLIFIER When a signal exceeds fHIGH-PASS, the AD8236 outputs the highpass filtered input signal. 0.1µF +IN fHIGH-PASS = 1 2πRC AD8236 R REF –IN C +VS 0.1µF AD8603 +VS VREF 10µF Figure 41. AC-Coupled Circuit Rev. 0 | Page 18 of 20 08000-142 An integrator can be tied to the AD8236 in feedback to create a high-pass filter as shown in Figure 41. This circuit can be used to reject dc voltages and offsets.
PAGE 19
AD8236 This circuit was designed and tested using the AD8609, low power, quad op amp. The fourth op amp is configured as a Schmitt trigger to indicate if the right arm or left arm electrodes fall off the body. Used in conjunction with the 953 kΩ resistors at the inputs of the AD8236, the resistors pull the inputs apart when the electrodes fall off the body. The Schmitt trigger sends an active low signal to indicate a leads off condition.
PAGE 20
AD8236 OUTLINE DIMENSIONS 3.20 3.00 2.80 8 3.20 3.00 2.80 1 5 5.15 4.90 4.65 4 PIN 1 0.65 BSC 0.95 0.85 0.75 1.10 MAX 0.15 0.00 0.38 0.22 COPLANARITY 0.10 0.23 0.08 8° 0° 0.80 0.60 0.40 SEATING PLANE COMPLIANT TO JEDEC STANDARDS MO-187-AA Figure 43.