LT1187 Linear Technology, LT1187 Datasheet - Page 10

• Manufacturer Part Number: LT1187
• Description: Low Power Video Difference Amplifier
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
LT1187
Using the Shutdown Feature
The LT1187 has a unique feature that allows the amplifier
to be shutdown 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 20k in parallel with the feedback resistors.
For MUX applications, the amplifiers may be configured
inverting, noninverting, or differential. When the output is
loaded with as little 1k from the amplifier’s feedback
resistors, the amplifier shuts off in 600ns. This shutoff can
be under the control of HC CMOS operating between 0V
and –5V.
The ability to maintain shutoff is shown on the curve
Shutdown Supply Current vs Temperature in the Typical
10
SHUTDOWN
V
B
OUT
A
C
(A) STANDARD INPUTS, PINS 2 TO 3, V
(B) EXTENDED INPUTS, PINS 2 TO 2, V
(C) EXTENDED INPUTS, PINS 1 TO 2, V
1MHz Sine Wave Gated Off with Shutdown Pin
A
V
= 2, R
FB
= R
G
LT1187 in Unity Gain
U U
= 1k
–
. In shutdown, the amplifier
IN
IN
IN
= 1.0V
= 2.0V
= 1.0V
W
P-P
P-P
P-P
LT1187 • AI06
LT1187 • AI07
U
Performance Characteristics section. At very high el-
evated temperature it is important to hold the shutdown
pin close to the negative supply to keep the supply current
from increasing.
Send Color Video Over Twisted-Pair
With an LT1187 it is possible to send and receive color
composite video signals more than 1000 feet on a low cost
twisted-pair. A bidirectional “video bus” consists of the
LT1195 op amp and the LT1187 video difference amplifier.
A pair of LT1195s at TRANSMIT 1, is used to generate
differential signals to drive the line which is back-termi-
nated in its characteristic impedance. The LT1187, twisted-
pair receiver, converts signals from differential to single-
ended. Topology of the LT1187 provides for cable com-
pensation at the amplifier’s feedback node as shown. In
this case, 1000 feet of twisted-pair is compensated with
1000pF and 50
system from 750kHz to 4MHz. This bandwidth is adequate
to pass a 3.58MHz chroma subcarrier, and the 4.5MHz
sound subcarrier. Attenuation in the cable can be compen-
sated by lowering the gain set resistor R
2, another pair of LT1195s serve the dual function to
provide cable termination via low output impedance, and
generate differential signals for TRANSMIT 2. Cable termi-
nation is made up of a 15 and 33 attenuator to reduce
the differential input signal to the LT1187. Maximum input
signal for the LT1187 is 760mV
1.5MHz Square Wave Input and Unequalized Response Through
1000 Feet of Twisted-Pair
to boost the 3dB bandwidth of the
P-P
.
G
. At TRANSMIT
LT1187 • AI08