LT1396 Linear Technology Corporation, LT1396 Datasheet - Page 11

• Manufacturer Part Number: LT1396
• Description: Dual 400mhz Current Feedback Amplifier
• Manufacturer: Linear Technology Corporation

it is important to keep the EN pin at least 3V below the V
supply. If a V
will remain enabled at all times, then the EN pin should be
tied to the V
mately 30µA when activated. If using CMOS open-drain
logic, an external 1k pull-up resistor is recommended to
ensure that the LT1395CS6 remains disabled in spite of
any CMOS drain leakage currents.
The enable/disable times are very fast when driven from
standard 5V CMOS logic. The LT1395CS6 enables in
about 30ns (50% point to 50% point) while operating on
±5V supplies (Figure 2). Likewise, the disable time is
approximately 40ns (50% point to 50% point) (Figure 3).
A
PPLICATI
V
V
V
V
Figure 3. Amplifier Disable Time, A
S
IN
S
IN
Figure 2. Amplifier Enable Time, A
= ±5V
–
= ±5V
= 1V
+
= 1V
supply. The enable pin current is approxi-
of less than 3V is desired, and the amplifier
O
R
R
R
R
F
G
F
G
U
= 255Ω
= 255Ω
= 255Ω
= 255Ω
S
I FOR ATIO
U
R
R
L
L
= 100Ω
= 100Ω
W
1395/6/7 F02
1395/6/7 F03
V
V
= 2
= 2
OUTPUT
EN
OUTPUT
EN
U
+
Differential Input Signal Swing
To avoid any breakdown condition on the input transis-
tors, the differential input swing must be limited to ±5V. In
normal operation, the differential voltage between the
input pins is small, so the ±5V limit is not an issue.
Buffered RGB to Color-Difference Matrix
An LT1397 can be used to create buffered color-differ-
ence signals from RGB inputs (Figure 4). In this applica-
tion, the R input arrives via 75Ω coax. It is routed to the
noninverting input of LT1397 amplifier A1 and to a 845Ω
resistor R8. There is also an 82.5Ω termination resistor
R11, which yields a 75Ω input impedance at the R input
when considered in parallel with R8. R8 connects to the
inverting input of a second LT1397 amplifier (A2), which
also sums the weighted G and B inputs to create a
–0.5 • Y output. LT1397 amplifier A3 then takes the
–0.5 • Y output and amplifies it by a gain of –2, resulting
in the Y output. Amplifier A1 is configured in a noninvert-
ing gain of 2 with the bottom of the gain resistor R2 tied
to the Y output. The output of amplifier A1 thus results in
the color-difference output R-Y.
The B input is similar to the R input. It arrives via 75Ω
coax, and is routed to the noninverting input of LT1397
amplifier A4, and to a 2320Ω resistor R10. There is also
a 76.8Ω termination resistor R13, which yields a 75Ω
SOURCES
R
G
B
75Ω
Figure 4. Buffered RGB to Color-Difference Matrix
ALL RESISTORS 1%
V
R11
82.5Ω
R12
90.9Ω
R13
76.8Ω
S
= ±5V
2320Ω
845Ω
432Ω
R10
R8
R9
LT1395/LT1396/LT1397
1/4 LT1397
–
+
A2
255Ω
R7
127Ω
R6
1/4 LT1397
–
–
1/4 LT1397
–
+
1/4 LT1397
+
+
A3
A4
A1
255Ω
R5
11
1395/6/7 F04
R1
255Ω
R2
255Ω
R4
255Ω
R3
255Ω
139567fc
R-Y
Y
B-Y