LT1218L Linear Technology Corporation, LT1218L Datasheet - Page 13

• Manufacturer Part Number: LT1218L
• Description: Precision Rail-to-rail Input And Output Op Amp
• Manufacturer: Linear Technology Corporation

APPLICATIONS
Shutdown
The biasing of the LT1218/LT1219 is controlled by the
SHDN pin. When the SHDN pin is low, the part is shut
down. In the shutdown mode, the output looks like a 40pF
capacitor and the supply current is less than 30 A. The
SHDN pin is referenced to the positive supply through an
internal bias circuit (see Figure 1). The SHDN pin current
with the pin low is typically 3 A.
The switching time between the shutdown and active
states is about 20 s, however, the total time to settle will
be greater by the slew time of the amplifier. For example,
if the DC voltage at the amplifier output is 0V in shutdown
and –2V in the active mode, an additional 20 s is required.
Figures 4a and 4b show the switching waveforms for a
sinusoidal and a –2V DC input to the LT1218.
SHDN
SHDN
V
V
OUT
OUT
R
V
R
V
L
S
L
S
= 10V
= 2.5V
= 10V
= 2.5V
U
Figure 4a
Figure 4b
INFORMATION
U
W
LT1218/19 • F04a
LT1218/19 • F04a
0V
0V
0V
0V
U
The SHDN pin can be driven directly from CMOS logic if the
logic and the LT1218/LT1219 are operated from the same
supplies. For higher supply operation, an interface is
required. An easy way to interface between supplies is to
use open-drain logic, an example is shown in Figure 5.
Because the SHDN pin is referenced to the positive supply,
the logic used should have a breakdown voltage greater
than the positive supply.
Trim Pins
Trim pins are provided for compatibility with other single
op amps. Input offset voltage can be adjusted over a
Improved Supply Rejection in the LT1219
The LT1219 is a variation of the LT1218 offering greater
supply rejection and lower high frequency output imped-
ance. The LT1219 requires a 0.1 F load capacitance for
2.3mV range with a 10k potentiometer.
Figure 6. Optional Offset Nulling
Figure 5. Shutdown Interface
SHDN
2
3
–
+
V
LT1218/
LT1219
1
–
4
10k
+
–
5V
–15V
15V
8
74C906
SHDN
7
LT1218/
LT1219
LT1218/LT1219
LT1218/19 • F05
LT1218/19 • F06
V
OUT
+
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