LTC1968 Precision Wide Bandwidth, RMS-to-DC Converter FEATURES DESCRIPTIO High Linearity: The LTC 1968 is a true RMS-to-DC converter that uses an 0.02% Linearity Allows Simple System Calibration innovative delta-sigma computational technique. The ben- Wide Input Bandwidth: efits of the LTC1968 proprietary architecture, when com- Bandwidth to 1% Additional Gain Error: 500kHz pared to conventional log-antilog RMS-to-DC converters, Bandwidth to 0.1% Additional Gain Error: 150kHz are higher linearity and accuracy, bandwidth independent 3dB Bandwidth Independent of Input Voltage of amplitude and improved temperature behavior. Amplitude The LTC1968 operates with single-ended or differential in- No-Hassle Simplicity: put signals and accurately supports crest factors up to 4. True RMS-DC Conversion with Only One External Common mode input range is rail-to-rail. Differential in- Capacitor put range is 1V , and offers unprecedented linearity. The PEAK Delta Sigma Conversion Technology LTC1968 allows hassle-free system calibration at any in- Ultralow Shutdown Current: put voltage. 0.1A The LTC1968 has a rail-to-rail output with a separate out- Flexible Inputs: put reference pin providing flexible level shifting it oper- Differential or Single Ended ates on a single power supply from 4.5V to 5.5V. A low power Rail-to-Rail Common Mode Voltage Range shutdown mode reduces supply current to 0.1A. Up to 1V Differential Voltage PEAK Flexible Output: The LTC1968 is packaged in the space-saving MSOP pack- Rail-to-Rail Output age, which is ideal for portable applications. Separate Output Reference Pin Allows Level Shifting , LTC and LT are registered trademarks of Linear Technology Corporation. Small Size: Protected under U.S. Patent Numbers 6,359,576, 6,362,677 and 6,516,291 Space Saving 8-Pin MSOP Package U APPLICATIO S True RMS Digital Multimeters and Panel Meters True RMS AC + DC Measurements TYPICAL APPLICATIO Linearity Performance 0.2 Single Supply RMS-to-DC Converter LTC1968, 0 4.5V TO 5.5V 0.2 + V IN1 OUTPUT 0.4 DIFFERENTIAL C + AVE LTC1968 V OUT INPUT 10F IN2 OUT RTN 0.6 CONVENTIONAL EN GND 0.1F LOG/ANTILOG OPT. AC 0.8 COUPLING 1968 TA01 60Hz SINEWAVE 1.0 0 100 200 300 400 500 1968 TA01b V (mV AC ) IN RMS 1968f 1 LINEARITY ERROR (V mV DC V mV AC ) OUT IN RMS U ULTC1968 UUW ABSOLUTE AXI U RATI GS PACKAGE/ORDER I FOR ATIO (Note 1) Supply Voltage ORDER PART + NUMBER V to GND ............................................................. 6V TOP VIEW Input Currents (Note 2) ..................................... 10mA LTC1968CMS8 GND 1 8 ENABLE + Output Current (Note 3) ..................................... 10mA IN1 2 7 V LTC1968IMS8 IN2 3 6 OUT RTN ENABLE Voltage ......................................... 0.3V to 6V NC 4 5 V OUT + OUT RTN Voltage........................................ 0.3V to V MS8 PACKAGE MS8 PART MARKING 8-LEAD PLASTIC MSOP Operating Temperature Range (Note 4) T = 150C, = 220C/ W JMAX JA LTC1968C/LTC1968I ......................... 40C to 85C LTAFG Specified Temperature Range (Note 5) LTC1968C/LTC1968I ......................... 40C to 85C Maximum Junction Temperature ......................... 150C Consult LTC Marketing for parts specified with wider operating temperature ranges. The temperature grade (I or C) is indicated on the shipping container. Storage Temperature Range ................ 65C to 150C Lead Temperature (Soldering, 10 sec)................. 300C ELECTRICAL CHARACTERISTICS The denotes specifications which apply over the full operating + temperature range, otherwise specifications are T = 25C. V = 5V, V = 2.5V, C = 10F, V = 200mV , V = 0.5V A OUTRTN AVE IN RMS ENABLE unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Conversion Accuracy G Low Frequency Gain Error 50Hz to 20kHz Input (Notes 6, 7) 0.1 0.3 % ERR 0.4 % V Output Offset Voltage (Notes 6, 7) 0.2 0.75 mV OOS V / T Output Offset Voltage Drift (Note 11) 210 V/C OOS LIN Linearity Error 50mV to 350mV (Notes 7, 8) 0.02 0.15 % ERR PSRRG Power Supply Rejection (Note 9) 0.02 0.20 %/V 0.25 %/V V Input Offset Voltage (Notes 6, 7, 10) 0.4 1.5 mV IOS V / T Input Offset Voltage Drift (Note 11) 210 V/C IOS Additional Error vs Crest Factor (CF) CF = 3 60Hz Fundamental, 200mV 0.2 mV RMS CF = 5 60Hz Fundamental, 200mV 5mV RMS Input Characteristics V Maximum Peak Input Swing Accuracy = 1% (Note 14) 1 1.05 V IMAX + I Input Voltage Range 0V V VR Z Input Impedance Average, Differential (Note 12) 1.2 M IN Average, Common Mode (Note 12) 100 M CMRRI Input Common Mode Rejection (Note 13) 50 400 V/V V Minimum RMS Input 5mV IMIN PSRRI Power Supply Rejection (Note 9) 250 700 V/V 1968f 2 U WWW