7.0 Reference Buffer for A-to-D Converters

The LMC7111 can be used as a voltage reference buffer for

analog-to-digital converters. This works best for A-to-D con-

verters whose reference input is a static load, such as dual

slope integrating A-to-Ds. Converters whose reference input

is a dynamic load (the reference current changes with time)

may need a faster device, such as the LMC7101 or the

LMC7131.

The small size of the LMC7111 allows it to be placed close to

the reference input. The low supply current (25 µA typical)

saves power.

For A-to-D reference inputs which require higher accuracy

and lower offset voltage, please see the LMC6462

datasheet. The LMC6462 has performance similar to the

LMC7111. The LMC6462 is available in two grades with re-

duced input voltage offset.

8.0 Dual and Quad Devices with Similar Performance

The LMC6462 and LMC6464 are dual and quad devices with

performance similar to the LMC7111. They are available in

both conventional through-hole and surface mount packag-

ing. Please see the LMC6462/4 datasheet for details.

9.0 SPICE Macromodel

A SPICE macromodel is available for the LMC7111. This

model includes simulation of:

•

Input common-mode voltage range

•

Frequency and transient response

•

Quiescent and dynamic supply current

•

Output swing dependence on loading conditions and

many more characteristics as listed on the macro model

disk. Contact your local National Semiconductor sales of-

fice to obtain an operational amplifier spice model library

disk.

10.0 Additional SOT23-5 Tiny

Devices

National Semiconductor has additional parts available in the

space saving SOT23 Tiny package, including amplifiers,

voltage references, and voltage regulators. These devices

include —

LMC7101 1 MHz gain-bandwidth rail-to-rail input and out-

put amplifier — high input impedance and high

gain, 700 µA typical current 2.7V, 3V, 5V and 15V

specifications.

LM7131

Tiny Video amp with 70 MHz gain bandwidth.

LMC7211 Comparator in a tiny package with rail-to-rail in-

put and push-pull output. Typical supply current

of 7 µA. Typical propagation delay of 7 µs. Speci-

fied at 2.7V, 5V and 15V supplies.

LMC7221 Comparator with an open drain output for use in

mixed voltage systems. Similar to the LMC7211,

DS012352-17

FIGURE 4. Stable Negative Bias

DS012352-18

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