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LT1193I

Video Difference Amplifier

Linear Technology 

LT1193

APPLICATIO S I FOR ATIO

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. The cable driver has

a – 3dB bandwidth of 80MHz while driving a 150Ω load.

Using the Shutdown Feature

The LT1193 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

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

dissipates 15mW while maintaining a true high impedance

output state of 15kΩ in parallel with the feedback resis-

tors. The amplifiers may be connected inverting, nonin-

verting or differential for MUX applications. When the

output is loaded with as little as 1kΩ from the amplifier’s

feedback resistors, the amplifier shuts off in 200ns. This

shutoff can be under the control of HC CMOS operating

between 0V and – 5V.

Output Shutdown

isolating the capacitance with 10Ω can be helpful. Precau-

tions primarily have to do with driving large

capacitive loads.

Other precautions include:

1. Use a ground plane (see Design Note 50, High Fre-

quency Amplifier Evaluation Board).

2. Do not use high source impedances. The input capaci-

tance of 2pF, and RS = 10k for instance, will give an

8MHz – 3dB bandwidth.

3. PC board socket may reduce stability.

4. A feedback resistor of 1k or lower reduces the effects of

stray capacitance at the inverting input. (For instance,

closed-loop gain of ±2 can use RFB = 300Ω and

RG = 300Ω.)

Driving Capacitive Load

tON = 300ns

tOFF = 200ns

LT1193 • TA12

1MHz SINE WAVE GATED OFF WITH

SHUTDOWN PIN, AV = 3, RFB = 1k, RG = 500Ω

The ability to maintain shutoff is shown on the curve

Shutdown Supply Current vs Temperature in the Typical

Performance Characteristics section. At very high el-

evated temperatures it is important to hold the SHDN pin

close to the negative supply to keep the supply current

from increasing.

Murphy Circuits

There are several precautions the user should take when

using the LT1193 in order to realize its full capability.

Although the LT1193 can drive a 30pF in gains as low as␣ 2,

10

LT1193 • TA14

AV = 2, IN DEMO BOARD, CL = 30pF, RFB = 1k, RG = 1k

Driving Capacitive Load

AV = 2, IN DEMO BOARD, CL = 30pF

WITH 10Ω ISOLATING RESISTOR

LT1193 • TA15

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