LT1795
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
+
and SHDNREF to ground.
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 200µA, or to control the quiescent current in
normal operation.
V
+
R
SHDN
10 SHDN
11 SHDNREF
1795 F01
Figure 1. R
SHDN
Connected Between V
+
and SHDN (Pin 10);
SHDNREF (Pin 11) = GND. See Figure 2
80
70
AMPLIFIER SUPPLY CURRENT,
I
SY
– mA (BOTH AMPLIFIERS)
T
A
= 25°C
V
S
=
±15V
AMPLIFIER SUPPLY CURRENT,
I
SY
– mA (BOTH AMPLIFIERS)
60
50
40
30
20
10
0
0
25
50
75 100 125 150 175 200 225
R
SHDN
(kΩ)
1795 F02
Figure 2. LT1795 Amplifier Supply Current vs R
SHDN
. R
SHDN
Connected Between V
+
and SHDN, SHDNREF = GND (See
Figure 1)
U
When V
SHDN
= V
SHDNREF
, the device is shut down. The
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 1.5µs.
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
+
– 1.5V. For
example, a 50k resistor between V
+
and SHDN will set the
V
+
10 SHDN
11 SHDNREF
R
SHDNREF
1795 F03
W
U
U
Figure 3. R
SHDNREF
Connected Between SHDNREF (Pin 11)
and GND; SHDN (Pin 10) = V
+
. See Figure 4
80
70
60
50
40
30
20
10
0
50 100 150 200 250 300 350 400 450 500
R
SHDNREF
(kΩ)
1795 F04
T
A
= 25°C
V
S
=
±15V
Figure 4. LT1795 Amplifier Supply Current vs R
SHDNREF
.
R
SHDNREF
Connected Between SHDNREF and GND,
SHDN = V
+
(See Figure 3)
7
LINER [ LINEAR TECHNOLOGY ]
