LT1367 Linear Technology Corporation, LT1367 Datasheet - Page 13

• Manufacturer Part Number: LT1367
• Description: Dual And Quad Precision Rail-to-rail Input And Output Op Amps
• Manufacturer: Linear Technology Corporation

APPLICATIONS
TYPICAL APPLICATIONS
Improved Supply Rejection in the LT1368/LT1369
The LT1368/LT1369 are variations of the LT1366/LT1367
offering greater supply rejection and lower high frequency
output impedance. The LT1368/LT1369 require a 0.1 F
load capacitance for compensation. The output capaci-
tance forms a filter, which reduces pickup from the supply
and lowers the output impedance. This additional filtering
is helpful in mixed analog/digital systems with common
supplies, or systems employing switching supplies. Filter-
ing also reduces high frequency noise, which may be
beneficial when driving A/D converters.
Buffering A/D Converters
Figure 5 shows the LT1368 driving an LTC
2-channel micropower A/D Converter (ADC). The LTC1288
can accommodate voltage references and input signals
equal to the supply rails. The sampling nature of this ADC
eliminates the need for an external sample-and-hold, but
may call for a drive amplifier because of the ADC’s 12 s
settling requirement. The LT1368’s rail-to-rail operation
and low input offset voltage make it well-suited for low
power, low frequency A/D applications. Either the LT1366
or LT1368 could be used for this application. However, for
low frequencies (f < 1kHz) the LT1368 provides better
supply rejection.
V
(AC)
OUT
V
+
Figure 4a. LT1366 Power Supply Rejection Test
U
INFORMATION
2 s/DIV
U
U
W
LT1366 F04a
U
®
1288
Figure 4 shows the outputs of the LT1366/LT1368 per-
turbed by a 200mV
positive supply. The LT1368’s power supply rejection is
about ten times greater than that of the LT1366 at 50kHz.
Note the 5-to-1 scale change in the output voltage traces.
The tolerance of the external compensation capacitor is
not critical. The plots of Overshoot vs Load Current in the
Typical Performance Characteristics section illustrate the
effect of a capacitive load.
V
V
0
1
V
(AC)
+
–
+
–
1/2 LT1368
1/2 LT1368
OUT
V
+
Figure 4b. LT1368 Power Supply Rejection Test
Figure 5. 2-Channel Low Power A/D Converter
P-P
0.1 F
0.1 F
0.1 F
50kHz square wave added to the
2 s/DIV
V
CC
CS/SHDN
CH0
CH1
GND
LT1366/LT1367
LT1368/LT1369
LTC1288
V
CC
(REF)
D
CLK
OUT
D
IN
LT1366 F04b
1 F
13
TO P
LT1366 FO5