LT1366/LT1367
LT1368/LT1369
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APPLICATIONS INFORMATION
Improved Supply Rejection in the LT1368/LT1369
Figure 4 shows the outputs of the LT1366/LT1368 per-
turbed by a 200mVP-P 50kHz square wave added to the
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 LT1368/LT1369 are variations of the LT1366/LT1367
offering greater supply rejection and lower high frequency
output impedance. The LT1368/LT1369 require a 0.1µF
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,orsystemsemployingswitchingsupplies.Filter-
ing also reduces high frequency noise, which may be
beneficial when driving A/D converters.
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)
VOUT
VOUT
2µs/DIV
LT1366 F04a
2µs/DIV
LT1366 F04b
Figure 4a. LT1366 Power Supply Rejection Test
Figure 4b. LT1368 Power Supply Rejection Test
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TYPICAL APPLICATIONS
Buffering A/D Converters
V
CC
Figure 5 shows the LT1368 driving an LTC®1288
2-channelmicropowerA/DConverter(ADC).TheLTC1288
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
orLT1368couldbeusedforthisapplication. However, for
low frequencies (f < 1kHz) the LT1368 provides better
supply rejection.
1µF
0.1µF
0.1µF
+
V
0
1/2 LT1368
CS/SHDN
CH0
V
(REF)
CC
–
TO µP
CLK
LTC1288
CH1
GND
D
OUT
D
+
IN
V
1
1/2 LT1368
–
0.1µF
LT1366 FO5
Figure 5. 2-Channel Low Power A/D Converter
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Linear [ Linear ]
