LT1399 Linear Technology Corporation, LT1399 Datasheet - Page 11

• Manufacturer Part Number: LT1399
• Description: Low Cost Dual And Triple 300mhz Current Feedback Amplifiers With Shutdown
• Manufacturer: Linear Technology Corporation

A
The enable/disable times are very fast when driven from
standard 5V CMOS logic. Each amplifier enables in about
30ns (50% point to 50% point) while operating on 5V
supplies (Figure 2). Likewise, the disable time is approxi-
mately 40ns (50% point to 50% point) (Figure 3).
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. In the
disabled mode however, the differential swing can be the
same as the input swing, and there is a risk of device
breakdown if input voltage range has not been properly
considered.
3-Input Video MUX Cable Driver
The application on the first page of this data sheet shows
a low cost, 3-input video MUX cable driver. The scope
photo below (Figure 4) displays the cable output of a
30MHz square wave driving 150 . In this circuit the
active amplifier is loaded by the sum of R
disabled amplifier. Resistor values have been chosen to
keep the total back termination at 75 while maintaining
a gain of 1 at the 75 load. The switching time between
any two channels is approximately 32ns when both
enable pins are driven.
When building the board, care was taken to minimize
trace lengths at the inverting input. The ground plane was
also pulled away from R
board to minimize stray capacitance.
PPLICATI
200mV/DIV
OUTPUT
R
R
f = 10MHz
L
F
= 150
= R
Figure 4. Square Wave Response
G
= 324
O
U
S
F
I FOR ATIO
5ns/DIV
U
and R
G
on both sides of the
W
F
1398/99 F04
and R
U
G
of each
Using the LT1399 to Drive LCD Displays
Driving the current crop of XGA and UXGA LCD displays
can be a difficult problem because they require drive
voltages of up to 12V, are usually a capacitive load of over
300pF, and require fast settling. The LT1399HV is par-
ticularly well suited for driving these LCD displays be-
cause it is capable of swinging more than 6V on 7.5V
supplies, and it can drive large capacitive loads with a
small series resistor at the output, minimizing settling
time. As seen in Figures 6 and 7, at a gain of +3 with a
16.9
LT1399HV is capable of settling to 0.1% in 30ns for a 6V
step. Similarly, a 12V output step settles in 70ns.
Figure 5. 3-Input Video MUX Switching Response (A
Figure 6. LT1399/LT1399HV Large-Signal Pulse Response
V
OUT
V
output series resistor and a 330pF load, the
IN
LT1398/LT1399/LT1399HV
V
V
at 3.58MHz
V
R
R
R
C
S
INA
S
F
G
S
L
= 5V
= 324
= 330pF
= 5V
= 162
= 16.9
= V
INB
= 2V
P-P
20ns/DIV
20ns/DIV
1398/99 AI06
1398/99 F05
sn13989 13989fas
EN A
EN B
OUTPUT
V
11
= 2)