Datasheet

LT1210
10
1210fb
For more information www.linear.com/LT1210
applicaTions inForMaTion
resistor speeds up the turn-off time and ensures that
the LT1210 is completely turned off. Because the pin is
referenced to the positive supply, the logic used should
have a breakdown voltage of greater than the positive
supply voltage. No other circuitry is necessary as the
internal circuit limits the Shutdown pin current to about
500µA. Figure 3 shows the resulting waveforms.
For applications where the full bandwidth of the amplifier
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 65
times the current in the Shutdown pin. The voltage across
the resistor in this condition is V
+
– 3V
BE
. For example, a
82k resistor will set the quiescent supply current to 9mA
with V
S
= ±15V.
The photos in Figures 4a and 4b show the effect of re-
ducing the quiescent supply current on the large-signal
response. The quiescent current can be reduced to 9mA
in the inverting configuration 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 amplifier is not independent of the amplifier gain
configuration. 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
Figure 2. Shutdown Interface
–
+
LT1210
SD
15V
–15V
R
F
R
G
V
IN
5V
24k
ENABLE
V
OUT
1210 F02
15V
74C906
Figure 3. Shutdown Operation
A
V
= 1
R
F
= 825Ω
R
L
= 50Ω
R
PULL-UP
= 24k
V
IN
= 1V
P-P
V
S
= ±15V
1210 F03
V
OUT
ENABLE
Figure 4a. Large-Signal Response vs I
Q
, A
V
= –1
Figure 4b. Large-Signal Response vs I
Q
, A
V
= 2
R
F
= 750Ω
R
L
= 10Ω
I
Q
= 9mA, 18mA, 36mA
V
S
= ±15V
1210 F04a
R
F
= 750Ω
R
L
= 10Ω
I
Q
= 9mA, 18mA, 36mA
V
S
= ±15V
1210 F04b
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