LTC2430IGN datasheet(37/40 Pages) LINER

37 / 40 page

LTC2430/LTC2431

24301f

temperature) will produce a worst-case error of –180ppm

at a noise gain of 3, such as would be encountered in an

inverting gain of 2, to produce –10V from a 5V reference.

The error associated with the 10V excitation would be

–80ppm. Hence, overall reference error could be as high

as 130ppm, the average of the two.

Figure 45 shows a similar scheme to provide excitation

using resistor arrays to produce precise gain. The circuit

is configured to provide 10V and –5V excitation to the

bridge, producing a common mode voltage at the input to

the LTC2430/LTC2431 of 2.5V, maximizing the AC input

range for applications where induced 60Hz could reach

amplitudes up to 2VRMS.

The circuits in Figures 43 and 45 could be used where

multiple bridge circuits are involved and bridge output can

be multiplexed onto a single LTC2430/LTC2431, via an

inexpensive multiplexer such as the 74HC4052.

Figure 44 shows the use of an LTC2430/LTC2431 with a

differential multiplexer. This is an inexpensive multiplexer

that will contribute some error due to leakage if used

directly with the output from the bridge, or if resistors are

inserted as a protection mechanism from overvoltage.

Although the bridge output may be within the input range

of the A/D and multiplexer in normal operation, some

thought should be given to fault conditions that could

result in full excitation voltage at the inputs to the multi-

plexer or ADC. The use of amplification prior to the

multiplexer will largely eliminate errors associated with

channel leakage developing error voltages in the source

impedance.

Complete 20-Bit Data Acquistion System in 0.1 Inch2

The LTC2430/LTC2431 provide 20-bit accuracy while

consuming a maximum of 300

µA. The MS package of the

LTC2431 makes it especially attractive in applications

where very limited space is available. A complete 20-bit

data acquisition system in 0.1 inch2 is shown in Figure 46

where the LTC2431 is powered by the LT1790 reference

family in an S6 package. A supply voltage from 0.25V

above the LT1790 output level to 20V enables the LT1790

to source up to 1mA and ensure the solid performance of

the LT2431.

The 3V, 3.3V, 4.096V and 5V versions of the LT1790 can

power the LTC2430/LTC2431 directly. Lower voltage ver-

sions will require a separate VCC supply of 2.7V to 5.5V for

the LTC2430/LTC2431.

2431 F44

REF+

REF–

IN+

IN–

VCC

GND

µF

TO OTHER

DEVICES

74HC4052

LTC2430/

LTC2431

Figure 44. Use a Differential Mulitplexer to Expand Channel Capability

APPLICATIO S I FOR ATIO

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