ANALOG DEVICES AD8278, AD8279 Service Manual

Low Power, Wide Supply Range,

Low Cost Difference Amplifiers, G = ½, 2

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 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 commonmode 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 commonmode 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.

Rev. B

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.

= 2.5 V

S

AD8278/AD8279

FUNCTIONAL BLOCK DIAGRAMS

+VS

7

40k 20k

2

–IN

40k

3 1

+IN

40k 20k

2

–INA

3 14

+INA

–INB

+INB

40k

40k 20k

6

5 8

40k

Table 1. Difference Amplifiers by Category

Low Distortion

High Voltage Current Sens ing

AD8270 AD628 AD8202 (U) AD8276 AD8271 AD629 AD8203 (U) AD8277 AD8273 AD8205 (B) AD8274 AD8206 (B) AMP03 AD8216 (B)

1

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.

AD8278

20k

4

–VS

Figure 1. AD8278

+VS

11

AD8279

20k

4

–VS

Figure 2. AD8279

5

SENSE

6

OUT

REF

12

SENSEA

13

OUTA

REFA

10

SENSEB

9

OUTB

REFB

1

Low Power

08308-001

08308-058

AD8278/AD8279

REVISION HISTORY

4/10—Rev. A to Rev. B

Changed Supply Current Parameters to AD8278 Supply Current

Parameter and AD8279 Supply Current Parameter, Table 5 ...... 6

Updated Outline Dimensions ....................................................... 20

10/09—Rev. 0 to Rev. A

Added AD8279 and 14-Lead SOIC Model ..................... Universal

Changes to Features .......................................................................... 1

Changes to General Description .................................................... 1

Change to Table 2 ............................................................................. 3

Change to Table 3 ............................................................................. 4

Change to Table 4 ............................................................................. 5

Typical Performance Characteristics ..............................................9

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

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

Driving the AD8278 and AD8279 ........................................... 16

Input Voltage Range ................................................................... 16

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

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

Configurations ............................................................................ 18 

Differential Output .................................................................... 19

Instrumentation Amplifier........................................................ 19

Outline Dimensions ....................................................................... 20

Ordering Guide .......................................................................... 21

Change to Table 5 .............................................................................. 6

Added Figure 6 and Table 9 ............................................................. 8

Changes to Figure 31 and Figure 32............................................. 13

Changes to Figure 40, Figure 41, and Figure 42 ......................... 14

Added Figure 47; Renumbered Sequentially .............................. 15

Changes to Figure 51 to Figure 57 ................................................ 18

Added Differential Output Section .............................................. 19

Changes to Figure 59 ...................................................................... 19

Updated Outline Dimensions ....................................................... 21

Changes to Ordering Guide .......................................................... 21

7/09—Revision 0: Initial Version

Rev. B | Page 2 of 24

AD8278/AD8279

SPECIFICATIONS

VS = ±5 V to ±15 V, V otherwise noted.

Table 2.

Parameter Conditions

INPUT CHARACTERISTICS

System Offset1 50 100 50 250 µV

Over Temperature TA = −40°C to +85°C 100 250 µV vs. Power Supply VS = ±5 V to ±18 V 2.5 5 µV/V Average Temperature

Coefficient T

Common-Mode Rejection

Ratio (RTI) Input Voltage Range2 −3 (VS + 0.1) +3 (VS − 1.5) −3 (VS + 0.1) +3 (VS − 1.5) V Impedance3

Differential 120 120 kΩ Common Mode 30 30 kΩ

DYNAMIC PERFORMANCE

Bandwidth 1 1 MHz Slew Rate 1.1 1.4 1.1 1.4 V/µs Channel Separation f = 1 kHz 130 130 dB Settling Time to 0.01% 10 V step on output,

Settling Time to 0.001% 10 10 µs

GAIN

Gain Error 0.005 0.02 0.01 0.05 % Gain Drift TA = −40°C to +85°C 1 5 ppm/°C Gain Nonlinearity V

OUTPUT CHARACTERISTICS

Output Voltage Swing4 V

Short-Circuit Current Limit ±15 ±15 mA Capacitive Load Drive 200 200 pF

NOISE5

Output Voltage Noise f = 0.1 Hz to 10 Hz 1.4 1.4 V p-p f = 1 kHz 47 50 47 50 nV/√Hz

POWER SUPPLY6

AD8278 Supply Current 200 200 A

Over Temperature TA = −40°C to +85°C 250 250 A

AD8279 Supply Current 300 350 300 350 A

Over Temperature TA = −40°C to +85°C 400 400 A

Operating Voltage Range7

TEMPERATURE RANGE

Operating Range −40 +125 −40 +125 °C

1

Includes input bias and offset current errors, RTO (referred to output).

2

The input voltage range may also be limited by absolute maximum input voltage or by the output swing. See the for details. Input Voltage Range

3

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

4

Output voltage swing varies with supply voltage and temperature. See Figur through for details. e 22 Figure 25

5

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

6

Supply current varies with supply voltage and temperature. See Figure and for details. 26 Figure 28

7

Unbalanced dual supplies can be used, such as −VS = −0.5 V and +VS = +2 V. The positive supply rail must be at least 2 V above the negative supply and reference

voltage.

= 0 V, TA = 25°C, RL = 10 k connected to ground, G = ½ difference amplifier configuration, unless

REF

G = ½

Grade B Grade A

Min Typ Max Min Typ Max

= −40°C to +85°C 0.3 1 2 5 µV/°C

A

VS = ±15 V, VCM = ±27 V,

= 0 Ω 80 74 dB

R

S

= 100 pF

C

L

= 20 V p-p 7 12 ppm

OUT

= ±15 V, RL = 10 kΩ

S

= −40°C to +85°C −VS + 0.2 +VS − 0.2 −VS + 0.2 +VS − 0.2 V

T

A

9 9 µs

±2 ±18 ±2 ±18 V

Unit

Rev. B | Page 3 of 24

AD8278/AD8279

VS = ±5 V to ±15 V, V otherwise noted.

Table 3.

Parameter Conditions

INPUT CHARACTERISTICS

System Offset1 100 200 100 500 µV

Over Temperature TA = −40°C to +85°C 200 500 µV vs. Power Supply VS = ±5 V to ±18 V 5 10 µV/V Average Temperature

Coefficient

Common-Mode

Rejection Ratio (RTI) Input Voltage Range2 −1.5 (VS + 0.1) +1.5 (VS − 1.5) −1.5 (VS + 0.1) +1.5 (VS − 1.5) V Impedance3

Differential 120 120 kΩ

Common Mode 30 30 kΩ

DYNAMIC PERFORMANCE

Bandwidth 550 550 kHz Slew Rate 1.1 1.4 1.1 1.4 V/µs Channel Separation f = 1 kHz 130 130 dB Settling Time to 0.01% 10 V step on output,

Settling Time to 0.001% 11 11 µs

GAIN

Gain Error 0.005 0.02 0.01 0.05 % Gain Drift TA = −40°C to +85°C 1 5 ppm/°C Gain Nonlinearity V

OUTPUT CHARACTERISTICS

Output Voltage Swing4 VS = ±15 V, RL = 10 kΩ,

Short-Circuit Current

Limit Capacitive Load Drive 350 350 pF

NOISE5

Output Voltage Noise f = 0.1 Hz to 10 Hz 2.8 2.8 V p-p f = 1 kHz 90 95 90 95 nV/√Hz

POWER SUPPLY6

AD8278 Supply Current 200 200 A

Over Temperature TA = −40°C to +85°C 250 250 A AD8279 Supply Current 300 350 300 350 A

Over Temperature TA = −40°C to +85°C 400 400 A Operating Voltage Range7

TEMPERATURE RANGE

Operating Range −40 +125 −40 +125 °C

1

Includes input bias and offset current errors, RTO (referred to output).

2

The input voltage range may also be limited by absolute maximum input voltage or by the output swing. See the section for details. Input Voltage Range

3

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

4

Output voltage swing varies with supply voltage and temperature. See Figur through for details. e 22 Figure 25

5

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

6

Supply current varies with supply voltage and temperature. See Figure and for details. 26 Figure 28

7

Unbalanced dual supplies can be used, such as −VS = −0.5 V and +VS = +2 V. The positive supply rail must be at least 2 V above the negative supply and reference

voltage.

= 0 V, TA = 25°C, RL = 10 k connected to ground, G = 2 difference amplifier configuration, unless

REF

G = 2

Grade B Grade A

Min Typ Max Min Typ Max

= −40°C to +85°C 0.6 2 2 5 µV/°C

T

A

VS = ±15 V, VCM = ±27 V,

= 0 Ω 86 80 dB

R

S

= 100 pF

C

L

= 20 V p-p 7 12 ppm

OUT

= −40°C to +85°C

T

A

−V

+ 0.2 +VS − 0.2 −VS + 0.2 +VS − 0.2 V

S

10 10 µs

±15 ±15 mA

±2 ±18 ±2 ±18 V

Unit

Rev. B | Page 4 of 24

AD8278/AD8279

VS = +2.7 V to <±5 V, V

otherwise noted.

Table 4.

Parameter Conditions

INPUT CHARACTERISTICS

System Offset1 75 150 75 250 µV

Over Temperature TA = −40°C to +85°C 150 250 µV vs. Power Supply VS = ±5 V to ±18 V 2.5 5 µV/V Average Temperature

Coefficient

Common-Mode Rejection

Ratio (RTI)

V

Input Voltage Range2 −3 (VS + 0.1) +3 (VS − 1.5) −3 (VS + 0.1) +3 (VS − 1.5) V Impedance3

Differential 120 120 kΩ Common Mode 30 30 kΩ

DYNAMIC PERFORMANCE

Bandwidth 870 870 kHz Slew Rate 1.3 1.3 V/µs Channel Separation f = 1 kHz 130 130 dB Settling Time to 0.01% 2 V step on output,

GAIN

Gain Error 0.005 0.02 0.01 0.05 % Gain Drift TA = −40°C to +85°C 1 5 ppm/°C

OUTPUT CHARACTERISTICS

Output Swing4 R

Short-Circuit Current Limit ±10 ±10 mA Capacitive Load Drive 200 200 pF

NOISE5

Output Voltage Noise f = 0.1 Hz to 10 Hz 1.4 1.4 V p-p f = 1 kHz 47 50 47 50 nV/√Hz

POWER SUPPLY6

AD8278 Supply Current TA = −40°C to +85°C 200 200 A AD8279 Supply Current TA = −40°C to +85°C 375 375 A Operating Voltage Range 2.0 36 2.0 36 V

TEMPERATURE RANGE

Operating Range −40 +125 −40 +125 °C

1

Includes input bias and offset current errors, RTO (referred to output).

2

The input voltage range may also be limited by absolute maximum input voltage or by the output swing. See the section for details. Input Voltage Range

3

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

4

Output voltage swing varies with supply voltage and temperature. See Figur through for details. e 22 Figure 25

5

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

6

Supply current varies with supply voltage and temperature. See Figure and for details. 27 Figure 28

= midsupply, TA = 25°C, RL = 10 k connected to midsupply, G = ½ difference amplifier configuration, unless

REF

G = ½

Grade B Grade A

Min Typ Max Min Typ Max

= −40°C to +85°C 0.3 1 2 5 µV/°C

T

A

VS = 2.7 V, VCM = 0 V to

= 0 Ω 80 74 dB

2.4 V, R

S

= ±5 V, VCM = −10 V

S

to +7 V, R

= 0 Ω 80 74 dB

S

= 100 pF, VS = 2.7 V

C

L

= 10 kΩ,

L

= −40°C to +85°C −VS + 0.1 +VS − 0.15 −VS + 0.1 +VS − 0.15 V

T

A

7 7 µs

Unit

Rev. B | Page 5 of 24

AD8278/AD8279

VS = +2.7 V to <±5 V, V otherwise noted.

Table 5.

Parameter Conditions

INPUT CHARACTERISTICS

System Offset1 150 300 150 500 µV

Over Temperature TA = −40°C to +85°C 300 500 µV

vs. Power Supply VS = ±5 V to ±18 V 5 10 µV/V

Average Temperature

Coefficient

Common-Mode Rejection

Ratio (RTI) V

Input Voltage Range2 −1.5 (VS + 0.1) +1.5 (VS − 1.5) −1.5 (VS + 0.1) +1.5 (VS − 1.5) V Impedance3

Differential 120 120 kΩ

Common Mode 30 30 kΩ

DYNAMIC PERFORMANCE

Bandwidth 450 450 kHz Slew Rate 1.3 1.3 V/µs Channel Separation f = 1 kHz 130 130 dB Settling Time to 0.01% 2 V step on output,

GAIN

Gain Error 0.005 0.02 0.01 0.05 % Gain Drift TA = −40°C to +85°C 1 5 ppm/°C

OUTPUT CHARACTERISTICS

Output Swing4 R

Short-Circuit Current Limit ±10 ±10 mA Capacitive Load Drive 200 200 pF

NOISE5

Output Voltage Noise f = 0.1 Hz to 10 Hz 2.8 2.8 V p-p f = 1 kHz 94 100 94 100 nV/√Hz

POWER SUPPLY6

AD8278 Supply Current TA = −40°C to +85°C 200 200 A AD8279 Supply Current TA = −40°C to +85°C 375 375 A Operating Voltage Range 2.0 36 2.0 36 V

TEMPERATURE RANGE

Operating Range −40 +125 −40 +125 °C

1

Includes input bias and offset current errors, RTO (referred to output).

2

The input voltage range may also be limited by absolute maximum input voltage or by the output swing. See the section for details. Input Voltage Range

3

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

4

Output voltage swing varies with supply voltage and temperature. See Figur through for details. e 22 Figure 25

5

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

6

Supply current varies with supply voltage and temperature. See Figure and for details. 27 Figure 28

= midsupply, TA = 25°C, RL = 10 k connected to midsupply, G = 2 difference amplifier configuration, unless

REF

G = 2

Grade B Grade A

Min Typ Max Min Typ Max

= −40°C to +85°C 0.6 2 3 5 µV/°C

T

A

VS = 2.7 V, VCM = 0 V to 2.4 V, R

= ±5 V, VCM = −10 V

S

to +7 V, R

= 0 Ω 86 80 dB

S

= 0 Ω 86 80 dB

S

= 100 pF, VS = 2.7 V

C

L

= 10 kΩ,

L

= −40°C to +85°C −VS + 0.1 +VS − 0.15 −VS + 0.1 +VS − 0.15 V

T

A

9 9 µs

Unit

Rev. B | Page 6 of 24

AD8278/AD8279

ABSOLUTE MAXIMUM RATINGS

2.0

Table 6.

Parameter Rating

Supply Voltage ±18 V

Maximum Voltage at Any Input Pin −VS + 40 V

Minimum Voltage at Any Input Pin +VS − 40 V

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

Specified Temperature Range −40°C to +85°C

Package Glass Transition Temperature (TG) 150°C

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 Tabl e 7 assume a 4-layer JEDEC standard

board with zero airflow.

Table 7. Thermal Resistance

Package Type θJA Unit

8-Lead MSOP 135 °C/W

8-Lead SOIC 121 °C/W

14-Lead SOIC 105 °C/W

MAXIMUM POWER DISSIPATION

The maximum safe power dissipation for the AD8278 and

AD8279 are limited by the associated rise in junction tempera-

ture (T

) on the die. At approximately 150°C, which is the glass

J

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.

1.6

1.2

0.8

0.4

MAXIMUM POWER DISSIPATION (W)

0

–50 0–25 255075100125

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). While the short-circuit condition itself does not damage the part, the heat generated by the condition can cause the part to exceed its maximum junction temperature, with corresponding negative effects on reliability. Figure 3 and Figure 29, combined with knowledge of the supply voltages and ambient temperature of the part, can be used to determine whether a short circuit will cause the part to exceed its maximum junction temperature.

ESD CAUTION

TJ MAX = 150°C

SOIC

= 121°C/W



JA

MSOP



= 135°C/W

JA

AMBIENT TEMERATURE (°C)

08308-002

Rev. B | Page 7 of 24

AD8278/AD8279

PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS

REF

1

2

–IN

+IN

3

(Not to Scale)

–VS

4

NC = NO CONNECT

AD8278

TOP VIEW

8

7

6

5

NC

+VS

OUT

SENSE

8308-003

Figure 4. MSOP Pin Configuration

Table 8. AD8278 Pin Function Descriptions

Pin No. Mnemonic Description

1 REF Reference Voltage Input. 2 −IN Inverting Input. 3 +IN Noninverting Input. 4 −VS Negative Supply. 5 SENSE Sense Terminal. 6 OUT Output. 7 +VS Positive Supply. 8 NC No Connect.

1

AD8278

–IN

2

TOP VIEW

+IN

3

(Not to Scale)

4

–VS

NC = NO CONNECT

Figure 5. SOIC Pin Configuration

8

7

6

5

NC

+VS

OUT

SENSE

8308-004

1

NC

2

–INA

3

+INA

4

–VS

5 10

+INB

6 9

–INB

7 8

NC

NC = NO CONNECT

Figure 6. 14-Lead SOIC Pin Configuration

Table 9. AD8279 Pin Function Descriptions

Pin No. Mnemonic Description

1 NC No Connect. 2 −INA Channel A Inverting Input. 3 +INA Channel A Noninverting Input. 4 −VS Negative Supply. 5 +INB Channel B Noninverting Input. 6 −INB Channel B Inverting Input. 7 NC No Connect. 8 REFB Channel B Reference Voltage Input. 9 OUTB Channel B Output. 10 SENSEB Channel B Sense Terminal. 11 +VS Positive Supply. 12 SENSEA Channel A Sense Terminal. 13 OUTA Channel A Output. 14 REFA Channel A Reference Voltage Input.

AD8279

TOP VIEW

(Not to Scale)

14

13

12

11

REFA

OUTA

SENSEA

+VS

SENSEB

OUTB

REFB

08308-059

Rev. B | Page 8 of 24

ANALOG DEVICES AD8278, AD8279 Service Manual

FEATURES

APPLICATIONS

GENERAL DESCRIPTION

FUNCTIONAL BLOCK DIAGRAMS

TABLE OF CONTENTS

REVISION HISTORY

SPECIFICATIONS

ABSOLUTE MAXIMUM RATINGS

THERMAL RESISTANCE

MAXIMUM POWER DISSIPATION

SHORT-CIRCUIT CURRENT

ESD CAUTION

PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS