LT1195 データシートの表示（PDF） - Linear Technology

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LT1195

Low Power, High Speed Operational Amplifier

Linear Technology 

LT1195

APPLICATIO S I FOR ATIO

Power Supply Bypassing

The LT1195 is quite tolerant of power supply bypassing.

In some applications a 0.1µF ceramic disc capacitor

placed 0.5 inches from the ampifier is all that is required.

In applications requiring good settling time, it is important

to use multiple bypass capacitors. A 0.1µF ceramic disc in

parallel with a 4.7µF tantalum is recommended.

Cable Terminations

The LT1195 operational amplifier has been optimized as a

low cost video cable driver. The ±20mA guaranteed output

current enables the LT1195 to easily deliver 6VP-P into

150Ω, while operating on ±5V supplies.

Double-Terminated Cable Driver

5V

3+ 7

LT1195

2–

4

RG

– 5V

6

75Ω CABLE

RFB

75Ω

1195 AI01

Cable Driver Voltage Gain vs Frequency

8

6

4

AV = 2

2

RFB = 1k

RG = 330Ω

0

–2

AV = 1

RFB = 1k

–4

RG = 1k

–6

–8

–10

VS = ±5V

TA = 25°C

–12

100k

1M

10M

FREQUENCY (Hz)

100M

1195 AI02

receiving end (75Ω to ground) to absorb unwanted en-

ergy. The best performance can be obtained by double

termination (75Ω in series with the output of the amplifier,

and 75Ω to ground at the other end of the cable). This

termination is preferred because reflected energy is ab-

sorbed at each end of the cable. When using the double

termination technique it is important to note that the signal

is attenuated by a factor of 2, or 6dB. This can be compen-

sated for by taking a gain of 2, or 6dB in the amplifier.

Using the Shutdown Feature

The LT1195 has a unique feature that allows the amplifier

to be shut down for conserving power, or for multiplexing

several amplifiers onto a common cable. The amplifier will

shutdown by taking Pin 5 to V –. In shutdown, the amplifier

dissipates 15mW while maintaining a true high impedance

output state of 15k in parallel with the feedback resistors.

The amplifiers must be used in a noninverting configura-

tion for MUX applications. In inverting configurations the

input signal is fed to the output through the feedback

components. The following scope photos show that with

very high RL, the output is truly high impedance; the

output slowly decays toward ground. Additionally, when

the output is loaded with as little as 1k the amplifier shuts

off in 700ns. This shutoff can be under the control of HC

CMOS operating between 0V and –5V.

Output Shutdown

When driving a cable it is important to terminate the cable

to avoid unwanted reflections. This can be done in one of

two ways: single termination or double termination. With

single termination, the cable must be terminated at the

1MHz SINE WAVE GATED OFF WITH SHUTDOWN PIN

AV = 1, RL = SCOPE PROBE

1195 AI03

1195fa

8

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