LT1367CS datasheet(13/20 Pages) LINER

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LT1366/LT1367

LT1368/LT1369

1366fb

applicaTions inForMaTion

Improved Supply Rejection in the LT1368/LT1369

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.

Figure4showstheoutputsoftheLT1366/LT1368perturbed

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 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.

2µs/DIV

VOUT

100mV/DIV

V+ (AC)

100mV/DIV

LT1366 F04a

2µs/DIV

VOUT

20mV/DIV

V+ (AC)

100mV/DIV

LT1366 F04b

Figure 4a. LT1366 Power Supply Rejection Test

Figure 4b. LT1368 Power Supply Rejection Test

Typical applicaTions

Buffering A/D Converters

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.

CS/SHDN

CH0

CH1

GND

VCC (REF)

CLK

DOUT

DIN

LTC1288

–

TO µP

1µF

0.1µF

VCC

1/2 LT1368

0.1µF

LT1366 FO5

Figure 5. 2-Channel Low Power A/D Converter

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