Datasheet

LT1206
10
1206fa
APPLICATIONS INFORMATION
For applications where the full bandwidth of the amplifi er
is not required, the quiescent current of the device may be
reduced by connecting a resistor from the shutdown pin
to ground. The quiescent current will be approximately 40
times the current in the shutdown pin. The voltage across
the resistor in this condition is V
+
– 3V
BE
. For example, a
60k resistor will set the quiescent supply current to 10mA
with V
S
= ±15V.
The photos (Figures 4a and 4b) show the effect of reducing
the quiescent supply current on the large-signal response.
The quiescent current can be reduced to 5mA in the invert-
ing confi guration without much change in response. In
noninverting mode, however, the slew rate is reduced as
the quiescent current is reduced.
Slew Rate
Unlike a traditional op amp, the slew rate of a current
feedback amplifi er is not independent of the amplifi er gain
confi guration. There are slew rate limitations in both the
input stage and the output stage. In the inverting mode,
and for higher gains in the noninverting mode, the signal
amplitude on the input pins is small and the overall slew
rate is that of the output stage. The input stage slew rate
is related to the quiescent current and will be reduced as
the supply current is reduced. The output slew rate is set
by the value of the feedback resistors and the internal
capacitance. Larger feedback resistors will reduce the slew
rate as will lower supply voltages, similar to the way the
bandwidth is reduced. The photos (Figures 5a, 5b and 5c)
show the large-signal response of the LT1206 for various
gain confi gurations. The slew rate varies from 860V/µs
for a gain of 1, to 1400V/µs for a gain of –1.
R
F
= 750Ω
R
L
= 50Ω
I
Q
= 5mA, 10mA, 20mA
V
S
= ±15V
50ns/DIV
1206 F04a
R
F
= 750Ω
R
L
= 50Ω
I
Q
= 5mA, 10mA, 20mA
V
S
= ±15V
50ns/DIV
1206 F04b
R
F
= 825Ω
R
L
= 50Ω
V
S
= ±15V
20ns/DIV
1206 F05a
R
F
= R
G
= 750Ω
R
L
= 50Ω
V
S
= ±15V
20ns/DIV
1206 F05b
Figure 4a. Large-Signal Response vs I
Q
, A
V
= –1
Figure 4b. Large-Signal Response vs I
Q
, A
V
= 2
Figure 5a. Large-Signal Response, A
V
= 1
Figure 5a. Large-Signal Response, A
V
= –1