LT1366/LT1367
LT1368/LT1369
applicaTions inForMaTion
Improved Supply Rejection in the LT1368/LT1369
Figure4showstheoutputsoftheLT1366/LT1368perturbed
by a 200mV 50kHz square wave added to the positive
P-P
The LT1368/LT1369 are variations of the LT1366/LT1367
offering greater supply rejection and lower high frequency
outputimpedance.TheLT1368/LT1369requirea0.1µFload
capacitance for compensation. The output capacitance
forms a filter, which reduces pickup from the supply and
lowers the output impedance. This additional filtering is
helpfulinmixedanalog/digitalsystemswithcommonsup-
plies, or systems employing switching supplies. Filtering
alsoreduceshighfrequencynoise,whichmaybebeneficial
when driving A/D converters.
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
(AC)
V
(AC)
100mV/DIV
100mV/DIV
V
V
OUT
OUT
20mV/DIV
100mV/DIV
LT1366 F04b
LT1366 F04a
2µs/DIV
2µs/DIV
Figure 4a. LT1366 Power Supply Rejection Test
Figure 4b. LT1368 Power Supply Rejection Test
Typical applicaTions
Buffering A/D Converters
V
CC
Figure 5 shows the LT1368 driving an LTC®1288 2-chan-
nel 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 12µs
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.
1µF
0.1µF
0.1µF
+
V
0
1/2 LT1368
CS/SHDN
V
(REF)
CC
–
TO µP
CH0
CLK
LTC1288
CH1
GND
D
OUT
D
+
IN
V
1
LT1366 FO5
1/2 LT1368
0.1µF
–
Figure 5. 2-Channel Low Power A/D Converter
1366fb
ꢀꢂ
Linear [ Linear ]
