LT1195 LINER [Linear Technology], LT1195 Datasheet - Page 8

• Manufacturer Part Number: LT1195
• Description: Low Power, High Speed Operational Amplifier
• Manufacturer: LINER [Linear Technology]

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
LT1195
Power Supply Bypassing
The LT1195 is quite tolerant of power supply bypassing.
In some applications a 0.1 F 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 0.1 F ceramic disc in
parallel with a 4.7 F 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 6V
150 , while operating on 5V supplies.
8
A
PPLICATI
–10
–12
Cable Driver Voltage Gain vs Frequency
R
–6
–8
–2
–4
G
8
6
4
2
0
100k
Double-Terminated Cable Driver
V
T
A
S
O
3
2
= 25°C
= ±5V
+
–
U
LT1195
–5V
1M
S
5V
FREQUENCY (Hz)
7
4
I FOR ATIO
U
A
R
R
V
FB
G
6
= 1
= 1k
= 1k
10M
R
FB
75
A
R
R
V
FB
G
= 2
= 330
W
= 1k
CABLE
100M
1195 AI02
75
1195 AI01
U
P-P
into
receiving end (75 to ground) to absorb unwanted en-
ergy. The best performance can be obtained by double
termination (75 in series with the output of the amplifier,
and 75 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
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 R
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.
1MHz SINE WAVE GATED OFF WITH SHUTDOWN PIN
A
V
= 1, R
L
, the output is truly high impedance; the
L
= SCOPE PROBE
Output Shutdown
–
. In shutdown, the amplifier
1195 AI03