Datasheet

ManualsBrandsANALOG DEVICES ManualsLinear ICsLinear IC - Op-amp, differential amplifier Differential MSOP 8

Low Power, Wide Supply Range,

Low Cost Difference Amplifiers, G = ½, 2

AD8278/AD8279

Rev. C

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

Wide input range beyond supplies

Rugged input overvoltage protection

Low supply current: 200 µA maximum (per amplifier)

Low power dissipation: 0.5 mW at V

= 2.5 V

Bandwidth: 1 MHz (G = ½)

CMRR: 80 dB minimum, dc to 20 kHz (G = ½, B Grade)

Low offset voltage drift: ±1 V/°C maximum (B Grade)

Low gain drift: 1 ppm/°C maximum (B Grade)

Enhanced slew rate: 1.4 V/µs

Wide power supply range

Single supply: 2 V to 36 V

Dual supplies: ±2 V to ±18 V

8-lead SOIC, 14-lead SOIC, and 8-lead MSOP packages

APPLICATIONS

Voltage measurement and monitoring

Current measurement and monitoring

Instrumentation amplifier building block

Portable, battery-powered equipment

Test and measurement

GENERAL DESCRIPTION

The AD8278 and AD8279 are general-purpose difference

amplifiers intended for precision signal conditioning in power

critical applications that require both high performance and low

power. The AD8278 and AD8279 provide exceptional common-

mode rejection ratio (80 dB) and high bandwidth while amplifying

input signals that are well beyond the supply rails. The on-chip

resistors are laser trimmed for excellent gain accuracy and high

CMRR. They also have extremely low gain drift vs. temperature.

The common-mode range of the amplifier extends to almost

triple the supply voltage (for G = ½), making the amplifer ideal

for single-supply applications that require a high common-

mode voltage range. The internal resistors and ESD circuitry at

the inputs also provide overvoltage protection to the op amp.

The AD8278 and AD8279 can be used as difference amplifiers with

G = ½ or G = 2. They can also be connected in a high precision,

single-ended configuration for non inverting and inverting gains of

−½, −2, +3, +2, +1½, +1, or +½. The AD8278 and AD8279

provide an integrated precision solution that has a smaller size,

lower cost, and better performance than a discrete alternative.

The AD8278 and AD8279 operate on single supplies (2.0 V to 36 V)

or dual supplies (±2 V to ±18 V). The maximum quiescent supply

current is 200 A, which is ideal for battery-operated and portable

systems. For unity-gain difference amplifiers with similar

performance, refer to the AD8276 and AD8277 data sheets.

FUNCTIONAL BLOCK DIAGRAMS

3 1

40k 20k

40k

–VS

+VS

–IN

+IN

SENSE

OUT

REF

20k

AD8278

08308-001

Figure 1. AD8278

3 14

40k 20k

40k

+VS

–INA

+INA

SENSEA

OUTA

REFA

20k

5 8

40k 20k

40k

–INB

+INB

SENSEB

OUTB

REFB

20k

AD8279

–VS

08308-058

Figure 2. AD8279

Table 1. Difference Amplifiers by Category

Low

Distortion High Voltage Current Sensing

Low Power

AD8270 AD628 AD8202 (U) AD8276

AD8271 AD629 AD8203 (U) AD8277

AD8273 AD8205 (B)

AD8274 AD8206 (B)

AMP03 AD8216 (B)

U = unidirectional, B = bidirectional.

The AD8278 is available in the space-saving 8-lead MSOP and

SOIC packages, and the AD8279 is offered in a 14-lead SOIC

package. Both are specified for performance over the industrial

temperature range of −40°C to +85°C and are fully RoHS

compliant.

Summary of content (24 pages)

PAGE 1
Low Power, Wide Supply Range, Low Cost Difference Amplifiers, G = ½, 2 AD8278/AD8279 FEATURES FUNCTIONAL BLOCK DIAGRAMS +VS Wide input range beyond supplies Rugged input overvoltage protection Low supply current: 200 μA maximum (per amplifier) Low power dissipation: 0.5 mW at VS = 2.5 V Bandwidth: 1 MHz (G = ½) CMRR: 80 dB minimum, dc to 20 kHz (G = ½, B Grade) Low offset voltage drift: ±1 μV/°C maximum (B Grade) Low gain drift: 1 ppm/°C maximum (B Grade) Enhanced slew rate: 1.
PAGE 2
AD8278/AD8279 TABLE OF CONTENTS Features .............................................................................................. 1 Typical Performance Characteristics ..............................................9 Applications....................................................................................... 1 Theory of Operation ...................................................................... 16 General Description ......................................................................
PAGE 3
AD8278/AD8279 SPECIFICATIONS VS = ±5 V to ±15 V, VREF = 0 V, TA = 25°C, RL = 10 kΩ connected to ground, G = ½ difference amplifier configuration, unless otherwise noted. Table 2. G=½ Parameter INPUT CHARACTERISTICS System Offset 1 Over Temperature vs. Power Supply Average Temperature Coefficient Common-Mode Rejection Ratio (RTI) Input Voltage Range 2 Impedance 3 Differential Common Mode DYNAMIC PERFORMANCE Bandwidth Slew Rate Channel Separation Settling Time to 0.01% Settling Time to 0.
PAGE 4
AD8278/AD8279 VS = ±5 V to ±15 V, VREF = 0 V, TA = 25°C, RL = 10 kΩ connected to ground, G = 2 difference amplifier configuration, unless otherwise noted. Table 3. G=2 Parameter INPUT CHARACTERISTICS System Offset 1 Over Temperature vs. Power Supply Average Temperature Coefficient Common-Mode Rejection Ratio (RTI) Input Voltage Range 2 Impedance 3 Differential Common Mode DYNAMIC PERFORMANCE Bandwidth Slew Rate Channel Separation Settling Time to 0.01% Settling Time to 0.
PAGE 5
AD8278/AD8279 VS = +2.7 V to <±5 V, VREF = midsupply, TA = 25°C, RL = 10 kΩ connected to midsupply, G = ½ difference amplifier configuration, unless otherwise noted. Table 4. G=½ Parameter INPUT CHARACTERISTICS System Offset 1 Over Temperature vs. Power Supply Average Temperature Coefficient Common-Mode Rejection Ratio (RTI) Input Voltage Range 2 Impedance 3 Differential Common Mode DYNAMIC PERFORMANCE Bandwidth Slew Rate Channel Separation Settling Time to 0.
PAGE 6
AD8278/AD8279 VS = +2.7 V to <±5 V, VREF = midsupply, TA = 25°C, RL = 10 kΩ connected to midsupply, G = 2 difference amplifier configuration, unless otherwise noted. Table 5. G=2 Parameter INPUT CHARACTERISTICS System Offset 1 Over Temperature vs. Power Supply Average Temperature Coefficient Common-Mode Rejection Ratio (RTI) Input Voltage Range 2 Impedance 3 Differential Common Mode DYNAMIC PERFORMANCE Bandwidth Slew Rate Channel Separation Settling Time to 0.
PAGE 7
AD8278/AD8279 ABSOLUTE MAXIMUM RATINGS 2.0 Table 6. THERMAL RESISTANCE SOIC θJA = 121°C/W 1.2 0.8 MSOP θJA = 135°C/W 0.4 0 –50 –25 0 25 50 75 100 125 AMBIENT TEMERATURE (°C) Figure 3. Maximum Power Dissipation vs. Ambient Temperature SHORT-CIRCUIT CURRENT The AD8278 and AD8279 have built-in, short-circuit protection that limits the output current (see Figure 29 for more information).
PAGE 8
AD8278/AD8279 8 NC REF 1 AD8278 7 –IN 2 TOP VIEW (Not to Scale) +VS 6 OUT 5 SENSE –IN 2 +IN 3 –VS 4 NC = NO CONNECT Description Reference Voltage Input. Inverting Input. Noninverting Input. Negative Supply. Sense Terminal. Output. Positive Supply. No Connect. NC 1 14 REFA –INA 2 +INA 3 13 OUTA AD8279 12 SENSEA –VS 4 11 +VS TOP VIEW 10 SENSEB (Not to Scale) 9 OUTB –INB 6 NC 7 8 REFB NC = NO CONNECT 08308-059 +INB 5 Figure 6. 14-Lead SOIC Pin Configuration Table 9.
PAGE 9
AD8278/AD8279 TYPICAL PERFORMANCE CHARACTERISTICS VS = ±15 V, TA = 25°C, RL = 10 kΩ connected to ground, G = ½ difference amplifier configuration, unless otherwise noted. 600 80 N = 3840 MEAN = –16.8 SD = 41.7673 60 500 SYSTEM OFFSET (µV) NUMBER OF HITS 40 400 300 200 20 0 –20 –40 –60 100 –150 –100 –50 0 50 100 REPRESENTATIVE DATA –100 –50 –35 –20 –5 10 08308-005 0 150 SYSTEM OFFSET VOLTAGE (µV) Figure 7.
PAGE 10
AD8278/AD8279 10 5 VREF = MIDSUPPLY VS = 5V VS = 5V 6 4 2 0 VS = 2.7V –2 –4 –6 2.5 3.5 4.5 5.5 1 12 –1 1.5 2.5 3.5 4.5 5.5 Figure 16. Input Common-Mode Voltage vs. Output Voltage, 5 V and 2.7 V Supplies, VREF = Midsupply, G = 2 6 VREF = 0V VS = 5V 5 COMMON-MODE VOLTAGE (V) VS = 5V 8 6 4 2 VS = 2.7V 0 0.5 OUTPUT VOLTAGE (V) VREF = 0V 10 –2 4 3 2 1 VS = 2.7V 0 1.5 2.5 3.5 4.5 5.5 OUTPUT VOLTAGE (V) –2 –0.5 08308-012 0.5 0.5 1.5 2.5 3.5 4.5 5.
PAGE 11
AD8278/AD8279 18 +VS –0.1 OUTPUT VOLTAGE SWING (V) REFERRED TO SUPPLY VOLTAGES 12 GAIN = 2 6 GAIN = ½ –6 –12 –18 –24 –30 TA = –40°C TA = +25°C TA = +85°C TA = +125°C +0.4 +0.3 +0.2 100k 1M 10M –VS 2 4 6 8 10 12 14 18 16 SUPPLY VOLTAGE (±VS) 08308-020 10k 08308-017 1k FREQUENCY (Hz) Figure 22. Output Voltage Swing vs. Supply Voltage and Temperature, RL = 10 kΩ Figure 19. Gain vs. Frequency, +2.7 V Single Supply 120 +VS –0.
PAGE 12
AD8278/AD8279 +VS 250 VREF = MIDSUPPLY 200 –1.0 SUPPLY CURRENT (µA) OUTPUT VOLTAGE SWING (V) REFERRED TO SUPPLY VOLTAGES –0.5 –1.5 –2.0 TA = –40°C TA = +25°C TA = +85°C TA = +125°C +2.0 +1.5 150 VS = ±15V 100 VS = +2.7V 50 +1.0 0 1 2 3 4 5 6 7 8 9 10 OUTPUT CURRENT (mA) 0 –50 08308-023 –VS –30 –10 10 30 50 70 90 110 130 TEMPERATURE (°C) Figure 25. Output Voltage Swing vs. IOUT and Temperature, VS = ±15 V 08308-026 +0.5 Figure 28. Supply Current per Channel vs.
PAGE 13
AD8278/AD8279 10 8 NONLINEARITY (2ppm/DIV) 6 4 1V/DIV 2 3.64µs TO 0.01% 4.12µs TO 0.001% 0 –2 0.002%/DIV –4 –8 4µs/DIV –4 –3 –2 –1 0 1 2 3 4 5 OUTPUT VOLTAGE (V) TIME (µs) 08308-029 –10 –5 Figure 31. Gain Nonlinearity, VS = ±15 V, RL ≥ 2 kΩ, G = ½ 08308-032 –6 Figure 34. Large Signal Pulse Response and Settling Time, 2 V Step, VS = 2.7 V, G = ½ 20 16 NONLINEARITY (2ppm/DIV) 12 8 5V/DIV 4 7.6µs TO 0.01% 9.68µs TO 0.001% 0 –4 0.
PAGE 14
AD8278/AD8279 5.0 4.5 VS = 5V 2V/DIV OUTPUT VOLTAGE (V p-p) 4.0 3.5 3.0 VS = 2.7V 2.5 2.0 1.5 1.0 10µs/DIV 0 100 1k 10k 100k 1M FREQUENCY (Hz) 08308-038 08308-035 0.5 Figure 40. Maximum Output Voltage vs. Frequency, VS = 5 V, 2.7 V 5V/DIV 20mV/DIV Figure 37. Large Signal Step Response, G = ½ 08308-036 CL = 100pF CL = 147pF CL = 247pF 10µs/DIV 40µs/DIV Figure 38. Large Signal Step Response, G = 2 08308-039 NO LOAD Figure 41.
PAGE 15
AD8278/AD8279 50 GAIN = 2 45 40 ±2V ±5V 30 1µV/DIV OVERSHOOT (%) 35 25 ±15V 20 GAIN = ½ ±18V 15 10 0 50 100 150 200 250 CAPACITIVE LOAD (pF) 1s/DIV 08308-041 0 Figure 46. 0.1 Hz to 10 Hz Voltage Noise Figure 43. Small Signal Overshoot vs. Capacitive Load, RL ≥ 2 kΩ, G = ½ 160 35 140 CHANNEL SEPARATION (dB) 30 ±2V 20 15 ±5V ±15V 10 ±18V 5 2kΩ LOAD 120 100 80 60 40 0 0 50 100 150 200 250 300 350 CAPACITIVE LOAD (pF) 08308-042 20 Figure 44. Small Signal Overshoot vs.
PAGE 16
AD8278/AD8279 THEORY OF OPERATION CIRCUIT INFORMATION AC Performance Each channel of the AD8278 and AD8279 consists of a low power, low noise op amp and four laser-trimmed on-chip resistors. These resistors can be externally connected to make a variety of amplifier configurations, including difference, noninverting, and inverting configurations.
PAGE 17
AD8278/AD8279 The AD8278 and AD8279 are typically specified at single and dual supplies, but they can be used with unbalanced supplies as well; for example, −VS = −5 V, +VS = +20 V. The difference between the two supplies must be kept below 36 V. The positive supply rail must be at least 2 V above the negative supply. The AD8278 and AD8279 operate extremely well over a very wide range of supply voltages.
PAGE 18
AD8278/AD8279 APPLICATIONS INFORMATION –IN The AD8278 and AD8279 can be configured in several ways (see Figure 51 to Figure 57). These configurations have excellent gain accuracy and gain drift because they rely on the internal matched resistors. Note that Figure 53 shows the AD8278 and AD8279 as difference amplifiers with a midsupply reference voltage at the noninverting input.
PAGE 19
AD8278/AD8279 The reference must be driven with a low impedance source to maintain the internal resistor ratio. An example using the low power, low noise OP1177 as a reference is shown in Figure 58. INCORRECT CORRECT AD8278 AD8278 REF REF V INSTRUMENTATION AMPLIFIER The AD8278 and AD8279 can be used as building blocks for a low power, low cost instrumentation amplifier. An instrumentation amplifier provides high impedance inputs and delivers high common-mode rejection.
PAGE 20
AD8278/AD8279 OUTLINE DIMENSIONS 5.00 (0.1968) 4.80 (0.1890) 8 4.00 (0.1574) 3.80 (0.1497) 5 1 4 1.27 (0.0500) BSC 0.25 (0.0098) 0.10 (0.0040) 6.20 (0.2441) 5.80 (0.2284) 1.75 (0.0688) 1.35 (0.0532) 0.51 (0.0201) 0.31 (0.0122) COPLANARITY 0.10 SEATING PLANE 0.50 (0.0196) 0.25 (0.0099) 45° 8° 0° 0.25 (0.0098) 0.17 (0.0067) 1.27 (0.0500) 0.40 (0.
PAGE 21
AD8278/AD8279 8.75 (0.3445) 8.55 (0.3366) 8 14 1 7 1.27 (0.0500) BSC 0.25 (0.0098) 0.10 (0.0039) COPLANARITY 0.10 0.51 (0.0201) 0.31 (0.0122) 6.20 (0.2441) 5.80 (0.2283) 0.50 (0.0197) 0.25 (0.0098) 1.75 (0.0689) 1.35 (0.0531) SEATING PLANE 45° 8° 0° 0.25 (0.0098) 0.17 (0.0067) 1.27 (0.0500) 0.40 (0.
PAGE 22
AD8278/AD8279 NOTES Rev.
PAGE 23
AD8278/AD8279 NOTES Rev.