LINEAR dn426f handbook
Contents
1. DESIGN NOTES 6 Channel SAR ADCs for Industrial Monitoring and Portable Instruments Design Note 426 Guy Hoover and Steve Logan The 14 bit LTC2351 14 is a 1 5Msps low power SAR ADC with six simultaneously sampled differential input channels Itoperates from a single 3V supply and features six independent sample and hold amplifiers and a single ADC The single ADC with multiple S HAs enables excellent range match 1mV between channels and channel to channel skew 200ps The versatile LTC2351 14 is ideally suited for industrial monitoring applications such as 3 phase power line monitoring to ensure line voltage compliance portable power line instrumentation power factor correction mo tor control and data acquisition These applications may be battery powered and it is here that the LTC2351 14 s LT1790 1 25 3V IN OUT 4 TURNS CR i CR8348 2500 N 120VAC LINE low power and small size are desirable Power consump tion is a mere 16 5mW which extends battery life The 3 wire serial interface means fewer pins than parallel output devices allowing the LTC2351 14 to fit in a32 pin 5mm x 5mm QFN package Power Line Monitoring Application Figure 1 shows atypical powerline monitoring application Current is sensed by a CR Magnetics CR8348 2500 N current transformer An LT1790 1 25 biases the output of the transformer to the middle of the LTC2351 14 input range giving2. ion With PCB real estate getting tighter and designers always searching for lower power ICs fast data acquisition can be a challenge The LTC2351 14 and other low power SAR converters make it possible to optimize solution size power and cost En ain a oH AE ALE A Ea Ae A CURRENT A 1 0 0 10 20 30 40 50 60 70 80 TIME ms dn426 F03 Figure 3 50W Incandescent Bulb Current 1 0 0 10 20 30 40 50 60 70 80 TIME ms dn426 F05 Figure 5 4W LED Bulb Current For applications help call 408 432 1900 Ext 2602 iy Ae Corporation 1630 McCarthy Blvd Milpitas CA 95035 7417 408 432 1900 FAX 408 434 0507 www linear com dn426f LT TP 1007 305K PRINTED IN THE USA TECHNOLOGY LINEAR TECHNOLOGY CORPORATION 2007
3. the inputs maximum swing A 6 1 trans former and 41 1 attenuator scale the line voltage and the transformer output is similarly biased SY LT LTC and LTM are registered trademarks of Linear Technology Corporation All other trademarks are the property of their respective owners Vcc Vpp OVpp CHO LTC2351 14 VREF 10uF f cow 14 BIT ADC F4 SCK SDO TO PROCESSOR CHANNELS 2 5 TO MEASURE TWO OTHER VI PAIRS DN426 F01 Figure 1 Typical Power Line Monitoring Application 10 07 426 Figure 2 shows the AC line voltage in Linear Technology s Mixed Signal lab The flattened peaks are typical of the voltage in an office building where many of the loads are nonlinear such as computer power supplies Figure 3 shows the current through a 50W incandescent bulb Figure 4 shows the current through a 15W compact fluorescent bulb and Figure 5 is the current through a 4W LED based bulb The SMHz full linear bandwidth of the LTC2351 14 allows analysis of high frequency components ital tal p ta Uy PAT I Ly Tt P UT A Ay A WEA NT At AT PE A Ay Ng UAW TT ee Py tt 250 0 10 20 30 40 50 60 70 80 TIME ms dn426 F02 Figure 2 Line Voltage 1 0 0 10 20 30 40 50 60 70 80 TIME ms dn426 F04 Figure 4 15W Compact Fluorescent Bulb Current Data Sheet Download www linear com of the line voltage and current limited in this case by the bandwidth of the sense transformers Conclus
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LINEAR dn426f handbook