LTC1968
Precision Wide Bandwidth,
RMS-to-DC Converter
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FEATURES
DESCRIPTIO
The LTC®1968 is a true RMS-to-DC converter that uses an
innovativedelta-sigmacomputationaltechnique.Theben-
efits of the LTC1968 proprietary architecture, when com-
pared to conventional log-antilog RMS-to-DC converters,
are higher linearity and accuracy, bandwidth independent
of amplitude and improved temperature behavior.
■
High Linearity:
0.02% Linearity Allows Simple System Calibration
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Wide Input Bandwidth:
Bandwidth to 1% Additional Gain Error: 500kHz
Bandwidth to 0.1% Additional Gain Error: 150kHz
3dB Bandwidth Independent of Input Voltage
Amplitude
TheLTC1968operateswithsingle-endedordifferentialin-
put signals and accurately supports crest factors up to 4.
Common mode input range is rail-to-rail. Differential in-
putrangeis1VPEAK,andoffersunprecedentedlinearity.The
LTC1968 allows hassle-free system calibration at any in-
put voltage.
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No-Hassle Simplicity:
True RMS-DC Conversion with Only One External
Capacitor
Delta Sigma Conversion Technology
Ultralow Shutdown Current:
0.1µA
Flexible Inputs:
Differential or Single Ended
Rail-to-Rail Common Mode Voltage Range
Up to 1VPEAK Differential Voltage
Flexible Output:
Rail-to-Rail Output
Separate Output Reference Pin Allows Level Shifting
Small Size:
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The LTC1968 has a rail-to-rail output with a separate out-
put reference pin providing flexible level shifting; it oper-
atesonasinglepowersupplyfrom4.5Vto5.5V.Alowpower
shutdown mode reduces supply current to 0.1µA.
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TheLTC1968ispackagedinthespace-savingMSOPpack-
age, which is ideal for portable applications.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Protected under U.S. Patent Numbers 6,359,576, 6,362,677 and 6,516,291
Space Saving 8-Pin MSOP Package
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APPLICATIO S
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True RMS Digital Multimeters and Panel Meters
True RMS AC + DC Measurements
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TYPICAL APPLICATIO
Linearity Performance
0.2
Single Supply RMS-to-DC Converter
LTC1968, ∆Σ
0
4.5V TO 5.5V
–0.2
–0.4
+
V
IN1
IN2
OUTPUT
LTC1968
C
AVE
10µF
DIFFERENTIAL
INPUT
+
–
V
OUT
OUT RTN
GND
–0.6
–0.8
–1.0
CONVENTIONAL
LOG/ANTILOG
EN
0.1µF
OPT. AC
COUPLING
1968 TA01
60Hz SINEWAVE
100 200
0
300
400
500
1968 TA01b
V
IN
(mV AC
)
RMS
1968f
1