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ISL55002

High Supply Voltage 200MHz Unity-Gain Stable Operational Amplifier


FN7497 Rev 4.00

July 27, 2006


The ISL55002 is a high speed, low power, low cost monolithic operational amplifier. The ISL55002 is unity-gain stable and features a 300V/µs slew rate and 200MHz bandwidth while requiring only 8.5mA of supply current per amplifier.

The power supply operating range of the ISL55002 is from

±15V down to ±2.5V. For single-supply operation, the ISL55002 operates from 30V down to 5V.

The ISL55002 also features an extremely wide output voltage swing of -12.75V/+13.4V with VS = ±15V and RL = 1k.

At a gain of +1, the ISL55002 has a -3dB bandwidth of 200MHz with a phase margin of 55°. Because of its conventional voltage-feedback topology, the ISL55002 allow the use of reactive or non-linear elements in its feedback network. This versatility combined with low cost and 140mA of output-current drive makes the ISL55002 an ideal choice for price-sensitive applications requiring low power and high speed.

The ISL55002 is available in an 8 Ld SO package and is specified for operation over the full -40°C to +85°C temperature range.

Ordering Information

Features

By setting the two PDMAX equations equal to each other, we can solve the output current and RLOAD to avoid the device overheat.

Power Supply Bypassing Printed Circuit Board Layout

As with any high frequency device, a good printed circuit board layout is necessary for optimum performance. Lead lengths should be as short as possible. The power supply pin must be well bypassed to reduce the risk of oscillation. For normal single supply operation, where the VS- pin is connected to the ground plane, a single 4.7µF tantalum capacitor in parallel with a 0.1µF ceramic capacitor from VS+ to GND will suffice. This same capacitor combination should be placed at each supply

pin to ground if split supplies are to be used. In this case, the VS- pin becomes the negative supply rail.

Printed Circuit Board Layout

For good AC performance, parasitic capacitance should be kept to minimum. Use of wire wound resistors should be avoided because of their additional series inductance. Use of sockets should also be avoided if possible. Sockets add parasitic inductance and capacitance that can result in compromised performance. Minimizing parasitic capacitance at the amplifier's inverting input pin is very important. The feedback resistor should be placed very close to the inverting input pin. Strip line design techniques are recommended for the signal traces.

Application Circuits

Sallen Key Low Pass Filter

A common and easy to implement filter taking advantage of the wide bandwidth, low offset and low power demands of the ISL55002. A derivation of the transfer function is provided for convenience (See Figure 28).

Sallen Key High Pass Filter

Again this useful filter benefits from the characteristics of the ISL55002. The transfer function is very similar to the low pass so only the results are presented (See Figure 29).


V2 K 1 RB

5V RA

C5 Vo K 1 V1


1nF

C1

R2C2s 1

Vo

V1 Vi 1 K V1 Vo Vi 0


R1

1k


R2

1k C


1nF


+ V+


VOUT

R1


H(s)

R2 1

C1s

K

2

V1 2

1nF

- V-

R7

1k

R1C1R2C2s ((1 K)R1C1 R1C2 R21C2)s 1

1

H( jw ) 1 w 2R C R C

RB

1k

RA C5

1 1 2 2

Holp K

wo 1

1 1 1 2 2 2

1k

1nF

R1C1R2C2

Q 1

V3 (1 K)

5V

R1C1

R2C2

R1C2

R2C1

R2C2 R1C1

Holp K

Equations simplify if we let all

FIGURE 28. SALLEN-KEY LOW PASS FILTER

wo 1 RC

Q 1

components be equal R=C

3 K

5V

V2 Holp K

C5 wo 1

1nF

C1

R1C1R2C2

Q 1

R1

V1 1k


R2

1k C2

1nF


1nF


+ V+


- V-


VOUT

R7

(1 K)

R1C1

R2C2

R1C2

R2C1

R2C2 R1C1


RB

1k

RA C5

1k


Holp


wo


K

4 K

2


Equations simplify if we let

1k


1nF


V3 5V

RC

Q 2

4 K

all components be equal R=C


FIGURE 29. SALLEN-KEY HIGH PASS FILTER


Differential Output Instrumentation Amplifier

The addition of a third amplifier to the conventional three amplifier instrumentation amplifier introduces the benefits of

eo3 = –1 + 2R2 RGe1 e2 eo = –21 + 2R2 RGe1 e2


eo4 = 1 + 2R2 RGe1 e2

differential signal realization, specifically the advantage of using common-mode rejection to remove coupled noise and ground potential errors inherent in remote transmission. This configuration also provides enhanced bandwidth, wider output

2f

C1 2

BW = ------------------

ADi

Strain Gauge

ADi

= –21 + 2R2

RG

swing and faster slew rate than conventional three amplifier solutions with only the cost of an additional amplifier and few resistors.

The strain gauge is an ideal application to take advantage of the moderate bandwidth and high accuracy of the ISL55002. The operation of the circuit is very straightforward. As the strain variable component resistor in the balanced bridge is

A1

e1 +

-


R2

R3 R3


A3

-

+


R3 R3


eo3

+

subjected to increasing strain, its resistance changes, resulting in an imbalance in the bridge. A voltage variation from the referenced high accuracy source is generated and translated to the difference amplifier through the buffer stage. This voltage difference as a function of the strain is converted into an output voltage.


RG

R3 R3


R2 A4

+

-

REF

eo


-


eo4

A2

- R3 R3

e2 +


FIGURE 30. DIFFERENTIAL OUTPUT AMPLIFIER



VARIABLE SUBJECT TO STRAIN


5

V

R

R

+ 1k

15 16

+ V2

- 5V C6


1nF


R17 1k

+ V+

0V -

1k

1k 1k

R18

1k


-


RF

1k


V-


C12


1nF

+ V4

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