AD8541(2004) データシートの表示（PDF） - Analog Devices

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AD8541
(Rev.:2004)

General-Purpose CMOS Rail-to-Rail Amplifiers

Analog Devices 

55

50

VS = 5V

45

40

VS = 2.7V

35

30

25

20

؊55 ؊35؊15 5 25 45 65 85 105 125 145

TEMPERATURE – ؇C

TPC 28. Supply Current per

Amplifier vs. Temperature

AD8541/AD8542/AD8544

1,000

900

800

VS = 2.7V AND 5V

AV = 1

TA = 25؇C

700

600

500

400

300

200

100

0

1k

10k 100k 1M

10M

FREQUENCY – Hz

100M

TPC 29. Closed-Loop Output

Impedance vs. Frequency

VS = 5V

AV = 1

MARKER SET @ 10kHz

MARKER READING: 37.6␮V/ Hz

TA = 25؇C

0

5

10

15

20

25

FREQUENCY – kHz

TPC 30. Voltage Noise

NOTES ON THE AD854x AMPLIFIERS

The AD8541/AD8542/AD8544 amplifiers are improved perfor-

mance general-purpose operational amplifiers. Performance has

been improved over previous amplifiers in several ways.

Lower Supply Current for 1 MHz Gain Bandwidth

The AD854x series typically uses 45 mA of current per amplifier.

This is much less than the 200 mA to 700 mA used in earlier

generation parts with similar performance. This makes the

AD854x series a good choice for upgrading portable designs for

longer battery life. Alternatively, additional functions and per-

formance can be added at the same current drain.

Higher Output Current

At 5 V single supply, the short-circuit current is typically 60 mA.

Even 1 V from the supply rail, the AD854x amplifiers can provide

30 mA, sourcing or sinking.

Sourcing and sinking are strong at lower voltages, with 15 mA

available at 2.7 V and 18 mA at 3.0 V. For even higher output

currents, please see the Analog Devices AD8531/AD8532/AD8534

parts, with output currents to 250 mA. Information on these

parts is available from your Analog Devices representative,

and data sheets are available at the Analog Devices website at

www.analog.com.

Better Performance at Lower Voltages

The AD854x family of parts has been designed to provide better

ac performance, at 3.0 V and 2.7 V, than previously available

parts. Typical gain-bandwidth product is close to 1 MHz at 2.7 V.

Voltage gain at 2.7 V and 3.0 V is typically 500,000. Phase margin

is typically over 60∞C, making the part easy to use.

APPLICATIONS

Notch Filter

The AD8542 has very high open-loop gain (especially with a

supply voltage below 4 V), which makes it useful for active filters

of all types. For example, Figure 1 illustrates the AD8542 in the

classic Twin-T Notch Filter design. The Twin-T Notch is desired

for simplicity, low output impedance, and minimal use of op

amps. In fact, this notch filter may be designed with only one op

amp if Q adjustment is not required. Simply remove U2 as illus-

trated in Figure 2. However, a major drawback to this circuit

topology is ensuring that all the Rs and Cs closely match. The

components must closely match or notch frequency offset and

drift will cause the circuit to no longer attenuate at the ideal

notch frequency. To achieve desired performance, 1% or

better component tolerances or special component screens

are usually required. One method to desensitize the circuit-

to-component mismatch is to increase R2 with respect to

R1, which lowers Q. A lower Q increases attenuation over a

wider frequency range but reduces attenuation at the peak

notch frequency.

R

100k⍀

R

100k⍀

C2

53.6␮F

5.0V

3 8 1/2 AD8542

U1

2

1

4

V OUT

R/2

50k⍀

2.5VREF

C

26.7nF

1

f0 = 2pRC

1

[ ] f0 =

R1

4 1؊

R1+R2

C

26.7nF

1/2 AD8542

5

7

U2 6

R2

2.5k⍀

R1

97.5k⍀

2.5VREF

Figure 1. 60 Hz Twin-T Notch Filter, Q = 10

5.0V

R

R

3 7 AD8541

VIN

2C

2

6

4

V OUT

2.5VREF

R/2

C

C

Figure 2. 60 Hz Twin-T Notch Filter, Q = • (Ideal)

Figure 3 shows another example of the AD8542 in a notch

filter circuit. The FNDR notch filter has fewer critical

matching requirements than the Twin-T Notch and for the

FNDR Q is directly proportional to a single resistor R1.

While matching component values is still important, it is also

REV. D

–9–

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