10
LT1193
1193fb
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.
APPLICATIO S I FOR ATIO
WUUU
LT1193 • TA12
1MHz SINE WAVE GATED OFF WITH
SHUTDOWN PIN, A
V
= 3, R
FB
= 1k, R
G
= 500Ω
t
OFF
= 200ns
t
ON
= 300ns
Driving Capacitive Load
Driving Capacitive Load
LT1193 • TA14
A
V
= 2, IN DEMO BOARD, C
L
= 30pF, R
FB
= 1k, R
G
= 1k
LT1193 • TA15
A
V
= 2, IN DEMO BOARD, C
L
= 30pF
WITH 10Ω ISOLATING RESISTOR
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 R
S
= 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 R
FB
= 300Ω and
R
G
= 300Ω.)
Output Shutdown
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,
