LT1795 Linear Technology, LT1795 Datasheet - Page 7

• Manufacturer Part Number: LT1795
• Description: Dual 500mA/50MHz Current Feedback Line Driver Amplifier
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
The LT1795 is a dual current feedback amplifier with high
output current drive capability. The amplifier is designed
to drive low impedance loads such as twisted-pair trans-
mission lines with excellent linearity.
SHUTDOWN/CURRENT SET
If the shutdown/current set feature is not used, connect
SHDN to V
The SHDN and SHDNREF pins control the biasing of the
two amplifiers. The pins can be used to either turn off the
amplifiers completely, reducing the quiescent current to
less then 200 A, or to control the quiescent current in
normal operation.
Figure 1. R
SHDNREF (Pin 11) = GND. See Figure 2
Figure 2. LT1795 Amplifier Supply Current vs R
Connected Between V
Figure 1)
+
SHDN
and SHDNREF to ground.
80
70
60
50
40
30
20
10
0
0
Connected Between V
R
25
SHDN
U
+
50
and SHDN, SHDNREF = GND (See
V
+
75 100 125 150 175 200 225
U
R
SHDN
10 SHDN
11 SHDNREF
(k )
1795 F01
W
+
and SHDN (Pin 10);
T
V
A
S
= 25 C
= 15V
1795 F02
SHDN
U
. R
SHDN
When V
device will interface directly with 3V or 5V CMOS logic
when SHDNREF is grounded and the control signal is
applied to the SHDN pin. Switching time between the
active and shutdown states is about 1.5 s.
Figures 1 to 4 illustrate how the SHDN and SHDNREF pins
can be used to reduce the amplifier quiescent current. In
both cases, an external resistor is used to set the current.
The two approaches are equivalent, however the required
resistor values are different. The quiescent current will be
approximately 115 times the current in the SHDN pin and
230 times the current in the SHDNREF pin. The voltage
across the resistor in either condition is V
example, a 50k resistor between V
Figure 3. R
and GND; SHDN (Pin 10) = V
Figure 4. LT1795 Amplifier Supply Current vs R
R
SHDN = V
SHDNREF
SHDN
80
70
60
50
40
30
20
10
0
SHDNREF
+
Connected Between SHDNREF and GND,
50 100 150 200 250 300 350 400 450 500
= V
(See Figure 3)
SHDNREF
R
SHDNREF
Connected Between SHDNREF (Pin 11)
R
SHDNREF
V
, the device is shut down. The
+
+
. See Figure 4
10 SHDN
11 SHDNREF
(k )
+
T
V
and SHDN will set the
1795 F03
A
S
= 25 C
= 15V
1795 F04
LT1795
+
– 1.5V. For
SHDNREF
.
7