LTC1968 Linear Integrated Systems, LTC1968 Datasheet
LTC1968
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LTC1968 Summary of contents
Page 1
... LTC1968 allows hassle-free system calibration at any in- put voltage. The LTC1968 has a rail-to-rail output with a separate out- put reference pin providing flexible level shifting; it oper- ates on a single power supply from 4.5V to 5.5V. A low power shutdown mode reduces supply current to 0.1µA. ...
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... Output Current (Note 3) ..................................... ±10mA ENABLE Voltage ......................................... –0. OUT RTN Voltage ........................................ –0. Operating Temperature Range (Note 4) LTC1968C/LTC1968I ......................... – 40°C to 85°C Specified Temperature Range (Note 5) LTC1968C/LTC1968I ......................... – 40°C to 85°C Maximum Junction Temperature ......................... 150°C Storage Temperature Range ................ – 65°C to 150°C Lead Temperature (Soldering, 10 sec)................. 300° ...
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... Note 6: High speed automatic testing cannot be performed with C = 10µF. The LTC1968 is 100% tested with C AVE Note 7: The LTC1968 is 100% tested with DC and 10kHz input signals. Measurements with DC inputs from 50mV to 350mV are used to calculate the four parameters and linearity error ...
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... LTC1968 W U TYPICAL PERFOR A CE CHARACTERISTICS www.DataSheet4U.com Gain and Offset vs Input Common Mode Voltage 0.5 50mV ≤ V ≤ 350mV IN 0.4 0.3 0.2 0.1 GAIN ERROR 0 V OOS –0.1 V IOS –0.2 –0.3 –0.4 –0.5 0 0.5 1.0 1.5 2.0 2.5 INPUT COMMON MODE VOLTAGE (V) Gain and Offset vs Supply Voltage 0.5 50mV ≤ V ≤ 350mV IN 0 ...
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... SUPPLY VOLTAGE (V) Input Signal Bandwidth vs RMS Value 1000 300 –3dB 200 100 1% ERROR 0 100 –100 1% ERROR –200 –300 –400 10k 100k 1M INPUT SIGNAL FREQUENCY (Hz) LTC1968 AC Linearity 0.20 SINEWAVES C = 10µF 0.15 AVE V = MIDSUPPLY IN2 0.10 1kHz 0.05 0 –0.05 –0.10 –0.15 –0. 100 200 ...
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... TO DC OUTPUT 0 10 100 10k 100k 1M 10M 1k INPUT FREQUENCY (Hz) 1967 G16 Output Noise vs Device 1 LTC1966 C = 1µF AVE 0.1 LTC1967 LTC1968 C = 1.5µ 6.8µF AVE AVE 0.01 1k 10k 100k 1M INPUT FREQUENCY (Hz) 1968 G19 AVE CAPACITOR CHOSEN FOR EACH DEVICE TO GIVE A 1 SECOND, 0.1% SETTLING TIME 1968f ...
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... AC and DC. Although Pin 6 is often tied to GND, it can also be tied to any arbitrary voltage: GND < OUT RTN < (Pin 7): Positive Voltage Supply. 4.5V to 5.5V. ENABLE (Pin 8): An Active-Low Enable Input. LTC1968 is debiased if open circuited or driven to V operation, pull to GND. 2 ⎡ ⎤ ( ...
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... For the purposes of this data sheet, “SCR Waveforms” refers to the ideal chopped sine wave, though the LTC1968 will do faithful RMS-to-DC conversion with real SCR waveforms as well. The case shown is for Θ = 90°, which corresponds to 50% of available power being delivered to the load. As noted in Table 1, when Θ ...
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... This topology is inherently more stable and linear than log/ antilog implementations primarily because all of the signal processing occurs in circuits with high gain op amps operating closed loop. More detail of the LTC1968 inner workings is shown in the Simplified Schematic towards the end of this data sheet. INPUT CIRCUITRY INPUT • ...
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... RMS value, the peak is necessarily present for at most 6.25% (1/16) of the time. The LTC1968 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 LTC1968 ...
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... C = 10µF and f AVE INPUT If the application calls for the output of the LTC1968 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. This trade-off is depicted in Figure 8. The peak ripple error can also be ...
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... The first one, shown in Figure 9a uses a coupling capacitor to one input while the other is grounded. This will remove the DC voltage difference from the input to the LTC1968, and it will therefore not be part of the resulting output voltage. Again, this connection will + ...
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... To convince oneself of this necessity, consider a pulse train of 50% duty cycle between 0mV and 100mV. At very low frequencies, the LTC1968 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 fall characteristics were symmetrical, the output would converge to 50mV ...
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... However, if the reason for choosing 220µ keep the peak error with a 10Hz input less than 0.2%, there is another way to achieve that result with a much improved settling time. 0.40 0.50 1968 F10a = 10µF Figure 10b. LTC1968 Falling Edge with C AVE C = 2.2µ 4.7µ 10µ 22µF 1 SETTLING TIME (SEC) ...
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... 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 LTC1968 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 initial rise of the LTC1968 will have enhanced slew rates with DC and very low frequency inputs due to saturation effects in the ∆Σ modulator. This is seen in Figure 14 in two ways. First, the 10µ ...
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... DC offset, the square of the input has frequency content at the input frequency and the filter must average out that lower frequency. So with waveforms, the re- quired value for C input frequency, using the same design curves presented in Figures and 17. LTC1968 C =1µ 0.47µ 0.22µF 100 C = 0.22µ 0.1µ ...
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... LTC1968 U U APPLICATIO S I FOR ATIO www.DataSheet4U.com 0.22µ 0.47µ 1µF 1 0.1 0.01 0 0.1µ 0.22µ 0.47µF 1 0.1 0.01 0.1 Crest factor, which is the peak to RMS ratio of a dynamic signal, also effects the required C AVE crest factor, more of the energy in the signal is concentrated into a smaller portion of the waveform, and the averaging has to ride out the long lull in signal activity ...
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... PEAK With C = 100µF, the droop is only – 0.37% to 249.1mV AVE and the peak/output ratio is just 4.015, which the LTC1968 has enough margin to handle without error. For crest factors less than 3.5, the selection of C previously described should be sufficient to avoid this droop and modulator saturation effect. But with crest factors above 3 ...
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... For instance 15.5k source resistance is used to drive the LTC1968, the sampling action of the input stage will drag down the voltage seen at the input pins with small spikes at every sample clock edge as the sample capacitor is connected to be charged ...
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... ADC such as the LTC2420. Its input impedance is 6.5MΩ, but only when it is sampling. Since this occurs only half the time at most directly loads the LTC1968, a gain error of –0.08% to –0.11% results. In fact, the LTC2420 DC input current is LTC1968 ...
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... These errors will vary from part to part, but with a specific LTC1968 and LTC2420 combination, the errors will be fixed, varying less than ±0.05% over temperature system that has digi- tal calibration can be quite accurate despite the nominal gain and offset error ...
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... DC-based calibration is preferable in many cases because a DC voltage of known, good accuracy is easier to gener- ate than such an AC calibration voltage. The only down side is that the LTC1968 input offset voltage plays a role therefore suggested that a DC-based calibration scheme check at least two points: ±full scale. Applying the ...
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... TROUBLESHOOTING GUIDE Top Ten LTC1968 Application Mistakes 1. Circuit won’t work–Dead On Arrival–no power drawn. – Probably forgot to enable the LTC1968 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. – ...
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... Output is noisy with >200kHz inputs. – This is a fundamental characteristic of this topol- ogy. The LTC1968 is designed to work very well with inputs of 100kHz or less. It works okay as high as 1MHz, but it is limited by aliased ∆Σ noise. Solution: Bandwidth limit the input or digitally filter the resulting output ...
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... T1 50Hz TO 400Hz AVE 0.1µF C12 C9 OUTPUT C11 A2 OUT RTN C10 CLOSED DURING SHUTDOWN 50k BLEED RESISTOR FOR C AVE + V IN1 LTC1968 V V 10Ω OUT OUT C AVE IN2 OUT RTN 10µF 10k GND EN 1968 TA03 10k T1: CR MAGNETICS CR8348-2500-N www.crmagnetics.com C AVE 1968 SS = 4mV ...
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... DETAIL “A” MAX SEATING PLANE 0.22 – 0.38 (.009 – .015) TYP LTC1968 RMS Noise Measurement 2.5V + 1mV OUT 1µV OF INPUT NOISE RMS LTC1968 1k IN1 V OUT IN2 OUT RTN GND EN 1968 TA05 0.1µF –2.5V BW ≈ 1kHz TO 100kHz INPUT SENSITIVITY = 1µV 0.52 (.0205 REF 3.00 ± ...
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... R4 2.49k – 5. R10 LTC1968 200k V OUT C4 OUT RTN 1µF GND EN COMMENTS 48µ 60µ 45µ Available in SO-8 or SOT-223 Q 375µV V OS(MAX) 40µ 800µ 1.2mA I , 150µ 150µ 3µ 14µ ...