13
LT1218/LT1219
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 30µA. 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 3µA.
The switching time between the shutdown and active
states is about 20µs, 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 20µs is required.
Figures 4a and 4b show the switching waveforms for a
sinusoidal and a –2V DC input to the LT1218.
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.
APPLICATIONS INFORMATION
WUU
U
V
OUT
SHDN
R
L
= 10V
V
S
= ±2.5V LT1218/19 • F04a
Figure 4a
V
OUT
SHDN
R
L
= 10V
V
S
= ±2.5V LT1218/19 • F04a
Figure 4b
0V
0V
0V
0V
+
–
–15V
15V
LT1218/
LT1219
LT1218/19 • F05
SHDN
5V
SHDN
74C906
Figure 5. Shutdown Interface
Trim Pins
Trim pins are provided for compatibility with other single
op amps. Input offset voltage can be adjusted over a
±2.3mV range with a 10k potentiometer.
–
+
2
3
4
1
8
7
10k
V
–
OUT
V
+
LT1218/
LT1219
LT1218/19 • F06
Figure 6. Optional Offset Nulling
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 0.1µF load capacitance for
