This Converter High Accuracy, Very Offset Offset Drift, Rail-to-Rail I

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This Converter High Accuracy, Very Offset Offset Drift, Rail-to-Rail I

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Design Solutions 1999 LTC2400 Differential Single-Ended Converter Single Supply
This Converter High Accuracy, Very Offset Offset Drift, Rail-to-Rail Input Common Mode Range "Live Zero" Kevin Hoskins Derek Redmayne SPECIFICATIONS
VREF 1019-2.5; RSOURCE (Balanced)
PARAMETER Input Voltage Range Zero Error Input Current Nonlinearity Noise (without averaging) Noise (averaged readings) Resolution (with averaged readings) Overall Accuracy (uncalibrated**) Supply Voltage Supply Current CMRR Common Mode Range CIRCUIT TOTAL (MEASURED) LTC2400 (UNITS) Text 0.21* 0.026* 17.6 17.6 µVRMS µVRMS Bits Bits
circuit uses simple voltage reference (the Schottky diode transistor) bias single-ended signal approximately 270mV above ground. single supply applications, this bias voltage circuit's "live zero" operation allows LTC1050 LTC2400 amplify convert signals that include inputs below ground. LTC1043 achieves best differential single-ended conversion when internal switching frequency operates nominal 300Hz, 0.01µF capacitor when capacitors used should film type such mylar polypropylene. Conversion accuracy enhanced placing guard shield around connecting shield LTC1043. This minimizes nonlinearity that results from stray capacitance transfer errors associated with Consult LTC1043 data sheet more information. good practice high precision circuits, keep lead lengths short possible minimize stray capacitance noise pickup. stated above, LTC1043 highest transfer accuracy when using capacitors. Using other value will compromise accuracy. example, 0.1µF will typically increase circuit's overall nonlinearity tenfold. LTC1050's closed-loop gain accuracy affected tolerance ratio gain-setting resistors. cost considerations preclude using tolerance resistors (0.02% better), processor which LTC2400 connected used perform software correction. Operated follower, LTC1050's gain linearity error less than 0.001%.
registered trademarks Linear Technology Corporation.
*Input referred noise with gain **Does include gain setting resistors, offset gain error removed
OPERATION circuit Figure ideal level differential signals, typically 2mV/ single supply applications features "live zero" operation. circuit combines LTC®1043 LTC1050 differential single-ended amplifier that input common mode range that includes power supplies. uses LTC1043 sample differential input voltage, holds transfers ground-referred capacitor completing conversion single-ended. voltage applied LTC1050's noninverting input amplified gain resistors (101X values shown). amplifier's output then converted digital value LTC2400.
Information furnished Linear Technology Corporation believed accurate reliable. However, responsibility assumed use. Linear Technology Corporation makes representation that interconnection circuits described herein will infringe existing patent rights.
Design Solutions
circuit uses 2.5V excite 2mV/V bridge, producing level output. Best performance achieved using bandwidth limiting shown attenuator LTC2400's input reduce input-referred noise. LTC1050's noise gain allows adequate headroom expected signal magnitude. This followed attenuator that reduces signal overall gain 16.8. This gain typical point where input-referred noise minimized. source errors thermocouple effects that occur soldered connections. Their effects most pronounced circuit's level portion, before LTC1050's output. temperature changes level circuitry's connections will cause linearity perturbations final conversion result. There effects minimized balancing thermocouple connections with reversed redundant connections sealing circuit against moving air. circuit's input current dependent input signal's common mode voltage. input current approximately 100nA VIN(CM) dropping zero VIN(CM) values vary from part part. Figure input analogous capacitor parallel with connected ground. LTC1043's nominal switch resistance between source capacitance.
0.1µF
LT1019-2.5 0.1µF BRIDGE- TYPICAL INPUT DIFFERENTIAL INPUT (EXT) KEEP SHORT 0.1µF 0.1µF
0.1µF LTC2400 100k 0.1% BETTER, 10ppm/°C
5.1k CHIP SELECT
LTC1050
5.1k
VREF
SERIAL DATA 5.1k 'HC14 EQUIVALENT
DSOL6
0.1µF
2mV/V
SERIAL CLOCK
4.3k 0.01µF LTC1043
1N5711 SINGLE POINT "STAR" CONNECTION
2N5210
Figure Single Supply Differential Single-Ended Converter Level Inputs with "Live Zero" Operation
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, 95035-7417
(408)432-1900 FAX: (408) 434-0507 www.linear-tech.com
dsol6 LT/TP 0599 PRINTED
LINEAR TECHNOLOGY CORPORATION 1999

This Converter High Accuracy, Very Offset Offset Drift, Rail-to-Rail I

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