LTC1966 Linear Technology, LTC1966 Datasheet
LTC1966
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LTC1966 Summary of contents
Page 1
... The LTC1966 also has a rail-to-rail output with a separate output reference pin providing flexible level shifting. The LTC1966 operates on a single power supply from 2.7V to 5.5V or dual supplies up to 5.5V. A low power shutdown mode reduces supply current to 0.5 A. ...
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... Output Current (Note 3) ..................................... 10mA ENABLE Voltage ..................... V SS OUT RTN Voltage .............................. V Operating Temperature Range (Note 4) LTC1966C/LTC1966I ......................... – Specified Temperature Range (Note 5) LTC1966C/LTC1966I ......................... – Maximum Junction Temperature ......................... 150 C Storage Temperature Range ................ – 150 C Lead Temperature (Soldering, 10 sec)................. 300 C ...
Page 3
... Note 4: The LTC1966C/LTC1966I are guaranteed functional over the operating temperature range of – Note 5: The LTC1966C is guaranteed to meet specified performance from The LTC1966C is designed, characterized and expected to meet specified performance from – but is not tested nor QA sampled at these temperatures. The LTC1966I is guaranteed to meet specified performance from – ...
Page 4
... These specifications apply with and constitute a 3-sigma variation of the output rumble. AVE 350mV and Note 16: The LTC1966 can operate down to 2.7V single supply but cannot SS SS – V – 350mV. The operate at 2.7V. This additional constraint ...
Page 5
... V 0.8 0.4 V IOS 0.6 0.3 0.4 0.2 GAIN ERROR 0.2 0 –0.2 –0.1 –0.4 –0.2 –0.6 –0.3 –0.8 –0.4 –1.0 –0 100 125 –6 1966 G07 LTC1966 0 0.4 = –5V SS 0.3 0.2 V OOS 0 IOS –0.1 –0.2 –0.3 –0.4 –0.5 – 100 125 TEMPERATURE ( C) 1966 G09 1 ...
Page 6
... LTC1966 W U TYPICAL PERFOR A CE CHARACTERISTICS www.DataSheet4U.com Gain and Offset vs V Supply DD 0 GND SS 0.4 0.3 V IOS 0.2 0.1 GAIN ERROR 0 –0.1 V OOS –0.2 –0.3 –0.4 –0.5 2.5 3.0 3.5 4.0 4.5 5.0 5.5 V (V) DD 1966 G10 AC Linearity 0.20 60HZ SINEWAVES 0.15 AVE V = GND IN2 0.10 0.05 0 –0.05 –0.10 –0.15 –0. 100 150 ...
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... INPUT FREQUENCY (kHz) Output Accuracy vs Signal Amplitude 10 1% ERROR 5 0 –5 –1% ERROR –10 –15 –20 10k 100k 1M 0 1966 G23 LTC1966 DC Transfer Function Near Zero GND IN2 THREE REPRESENTITIVE UNITS –5 –10 –20 –15 –10 –5 ...
Page 8
... V (V – Max Output). Best results are obtained when DD OUT RTN = GND. V (Pin 7): Positive Voltage Supply. 2.7V to 5.5V. DD ENABLE (Pin 8): An Active-Low Enable Input. LTC1966 is debiased if open circuited or driven to V operation, pull to GND, a logic low or even – ...
Page 9
... CONTACT LTC AND PLACE YOUR ORDER W U START NOT DO YOU SURE NEED TRUE RMS-TO-DC CONVERSION? YES DO YOU NO HAVE ANY LTC1966s YET? YES DID DO YOU WANT TO NO YOU ALREADY TRY OUT KNOW HOW TO USE THE THE LTC1966? LTC1966 FIRST? YES DID NO YOUR CIRCUIT ...
Page 10
... For the purposes of this data sheet, “SCR Waveforms” refers to the ideal chopped sine wave, though the LTC1966 will do faithful RMS-to-DC conversion with real SCR waveforms as well. The case shown is for = 90 , which corresponds to 50% ...
Page 11
... OUT ments, this filter is simply too large to implement on-chip, 1966 F03 but the LTC1966 needs only one capacitor on the output to implement the lowpass filter. The user can select this capacitor depending on frequency range and settling time requirements, as will be covered in the Design Cookbook section to follow ...
Page 12
... The LTC1966 performs very well with crest factors less and will respond with reduced accuracy to signals with higher crest factors. The high performance with crest factors less than 4 is directly attributable to the high linearity throughout the LTC1966 ...
Page 13
... The typical values shown, 5% peak ripple with 0.05% DC error, occur with C If the application calls for the output of the LTC1966 to feed a sampling or Nyquist A/D converter (or other circuitry that will not average out this double frequency ripple) a larger averaging capacitor can be used ...
Page 14
... If the leakage is a constant current leak, the I • R drop of the leak multiplied by the output impedance of the LTC1966 will create a constant offset of the output voltage. If the leak is Ohmic, the resistor divider formed with the LTC1966 output impedance will cause a gain error. For ...
Page 15
... This will remove the DC voltage difference from the input to the LTC1966, and it will therefore not be part of the resulting output voltage. Again, this connection will work well with dual supply configurations, but in single ...
Page 16
... To convince oneself of this necessity, consider a pulse train of 50% duty cycle between 0mV and 100mV. At very low frequencies, the LTC1966 will essentially track the input. But as the input frequency is increased, the average result will converge to the RMS value of the input. If the rise and 5 5 ...
Page 17
... 0.1 0.01 0.1 Figure 12. LTC1966 Settling Time with One Cap Averaging prior generation log/antilog RMS-to-DC converters, whose averaging time constants are dependent on the signal level, resulting in excruciatingly long waits for the output zero. The shape of the rising and falling edges will be dependent ...
Page 18
... First of all, the op amp can be operated split supply if a negative supply is available. Just the op amp would need to do so; the LTC1966 can remain single sup- ply. A second way to address this issue is to create a signal reference voltage a half volt or so above ground. This is most ...
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... The step responses of the LTC1966 with 1 F-only and with the two post filters are shown in Figure 15. This is the rising edge RMS output response to a 10Hz input starting ...
Page 20
... The filter designs presented here have minimal overshoot and ringing, but are somewhat sensitive to component mis- matches. Even the 12% tolerance of the LTC1966 output impedance can be enough to cause some ringing. The dashed lines indicate what can happen when 5% capaci- tors and 1% resistors are used ...
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... So for example, a 10% duty cycle pulse train from PEAK AVE input is effectively only 30Hz due to the DC asymmetry and is effectively only: f DESIGN for the purposes of Figures and 18. LTC1966 100 100 F ...
Page 22
... With DC inputs, the error caused by V positive or negative depending if the two have the same or as AVE opposing polarity. The total conversion error with a sine wave input using the typical values of the LTC1966 static errors is computed as follows (500mV AC) OUT = 500.600mV = 500mV + 0.120 and GAIN ...
Page 23
... Cookbook for a discussion of the DC conversion error with low frequency AC inputs. The LTC1966 bandwidth limita- tions cause additional errors with high frequency inputs. Another dynamic error is due to crest factor. The LTC1966 performance versus crest factor is shown in the Typical Performance Characteristics. Output Errors Versus Frequency ...
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... LTC2420. Its input impedance is 6.5M , but only when it is sampling. Since this occurs only half the time at most directly loads the LTC1966, a gain error of – 0.54% to – 0.73% results. In fact, the LTC2420 DC input current is not zero at 0V, but rather at one half its reference, so both ...
Page 25
... F22b Figure 22b. Interfacing to LTC2420 an output offset and a gain error will result. These errors will vary from part to part, but with a specific LTC1966 and LTC2420 combination, the errors will be fixed, varying less than 0.05% over temperature system that has digital calibration can be quite accurate despite the nomi- nal gain and offset error ...
Page 26
... Gain = Input Offset = Note: Calculation of and correction for input offset voltage are the only way in which the two LTC1966 inputs (IN1, IN2) are distinguishable from each other. The calculation above assumes the standard definition of offset; that a positive offset is the case of a positive voltage error inside the device that must be corrected by applying a like negative voltage outside ...
Page 27
... TROUBLESHOOTING GUIDE Top Ten LTC1966 Application Mistakes 1. Circuit won’t work–Dead On Arrival–no power drawn. – Probably forgot to enable the LTC1966 by pulling Pin 8 low. Solution: Tie Pin 8 to Pin 1. 2. Circuit won’t work, but draws power. Zero or very little output, single-ended input application. – ...
Page 28
... Output is noisy with >10kHz inputs. – This is a fundamental characteristic of this topol- ogy. The LTC1966 is designed to work very well with inputs of 1kHz or less. It works okay as high as 1MHz, but it is limited by aliased Solution: Bandwidth limit the input or digitally filter the resulting output ...
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... LTC1966 OUT C AVE IN2 OUT RTN 1 F 100k V GND EN SS 1966 TA08 100k 0.1 F T1: CR MAGNETICS CR8348-2500-N www.crmagnetics.com LTC1966 RMS-to-DC Converter LTC1966 IN1 V DC OUTPUT OUT C AVE PEAK IN2 OUT RTN GND 0.1 F 1966 TA05 DC OUTPUT V = 4mV /A OUT DC ...
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... LTC1966 PLIFIED SCHE ATIC www.DataSheet4U.com V DD GND IN1 2nd ORDER IN2 BIAS CONTROL MODULATOR – – C12 C9 OUTPUT C11 OUT RTN C10 CLOSED DURING SHUTDOWN 30k BLEED RESISTOR FOR C AVE C AVE 1966 SS ...
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... BSC 4.90 0.15 DETAIL “A” (1.93 .006) 0 – 6 TYP 0.53 0.015 1.10 (.021 .006) (.043) DETAIL “A” MAX SEATING PLANE 0.22 – 0.38 (.009 – .015) TYP LTC1966 0.52 (.206 REF 3.00 0.102 (.118 .004) NOTE 0.86 (.034) REF 0.13 0.076 (.005 .003) 0.65 MSOP (MS8) 0802 ( ...
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... LTC1966 10k 1/2 IN1 V OUT IN2 OUT RTN V GND EN SS –5V 0.1 F –5V 1966 TA10 100k BW 1kHz TO 100kHz INPUT SENSITIVITY = 1 V 75A Current Measurement 5V IN1 LTC1966 OUT C AVE IN2 OUT RTN GND EN SS –5V , 450pA I OS(MAX) OS(MAX) , 100pA I OS(MAX) , 2nA I OS(MAX) ...