LTC2431 Linear Technology, LTC2431 Datasheet
LTC2431
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LTC2431 Summary of contents
Page 1
... INL and 0.56ppm RMS noise. They use delta-sigma technology and provide single cycle settling time for multiplexed applications. Through a single pin, the LTC2430/LTC2431 can be configured for better than 110dB differential mode rejection at 50Hz or 60Hz 2%, or they can be driven by an external oscillator for a user-defined rejection frequency ...
Page 2
... V CC – GND (Notes 1, 2) Digital Output Voltage to GND ..... – 0. Operating Temperature Range + 0.3V) LTC2430C/LTC2431C .............................. LTC2430I/LTC2431I ........................... – 0.3V) Storage Temperature Range ................. – 150 0.3V) Lead Temperature (Soldering, 10 sec).................. 300 LTC2430CGN LTC2430IGN ...
Page 3
... Voltage – Voltage + Voltage – Voltage + GND CC – REF = – REF = GND CC LTC2430/LTC2431 MIN TYP MAX UNITS 110 120 dB 140 dB 140 dB 110 140 dB 110 140 dB 130 140 dB 110 dB 120 dB 120 dB MIN TYP MAX UNITS GND – ...
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... LTC2430/LTC2431 U U DIGITAL I PUTS A D DIGITAL OUTPUTS operating temperature range, otherwise specifications are at T SYMBOL PARAMETER V High Level Input Voltage IH CS Low Level Input Voltage IL CS High Level Input Voltage IH SCK V Low Level Input Voltage IL SCK I Digital Input Current ...
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... Note 11: The external oscillator is connected to the F oscillator frequency, f Note 12: The converter uses the internal oscillator Note 13: The output noise includes the contribution of the internal calibration operations. Note 14: Guaranteed by design and test correlation. = 153600Hz 2% = 128000Hz 2% LTC2430/LTC2431 MIN TYP MAX 5 2000 0.25 200 0.25 200 130.86 133 ...
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... LTC2430/LTC2431 W U TYPICAL PERFOR A CE CHARACTERISTICS Total Unadjusted Error ( 5V) CC REF REF 2.5V INCM INCM GND –1 –45 C –2 –3 –4 –5 –2 –1.5 0.5 1 1.5 2 –2.5 –1 – 0.5 0 2.5 INPUT VOLTAGE (V) 24301 G01 ...
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... – –2 REF = GND – GND INCM F = GND – – (V) REF 24301 G18 LTC2430/LTC2431 RMS Noise 3.4 + REF = 2.5V – REF = GND 3 GND INCM F = GND 3.0 2.8 2.6 2.4 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 V (V) CC ...
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... LTC2430/LTC2431 W U TYPICAL PERFOR A CE CHARACTERISTICS Full-Scale Error vs V REF – REF = GND GND 0.5V 10 INCM REF +FS ERROR 5 0 –5 –FS ERROR –10 –15 –20 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 V (V) REF 24301 G20 PSRR vs Frequency 4.1V CC ...
Page 9
... Sleep mode and remains in this low power state as long HIGH. A LOW-to-HIGH transition on CS during the Data Output transfer aborts the data transfer + – – extends and starts a new conversion. LTC2430/LTC2431 ) the SDO pin pin is connected pin is connected ...
Page 10
... LTC2430/LTC2431 CTIO S (LTC2431) SDO (Pin 8): Three-State Digital Output. During the Data Output period, this pin is used as the serial data output. When the chip select CS is HIGH ( high impedance state. During the Conversion and Sleep periods, this pin is used as the conversion status output ...
Page 11
... The LTC2430/LTC2431 incorporate a highly accurate on-chip oscillator. This eliminates the need for external frequency setting components such as crystals or oscillators. Clocked by the on-chip oscillator, the LTC2430/ LTC2431 achieve a minimum of 110dB rejection at the line frequency (50Hz or 60Hz 2%). Ease of Use The LTC2430/LTC2431 data output has no latency, filter settling delay or redundant data associated with the conversion cycle ...
Page 12
... CC ESD protection devices begin to turn on and the errors due input leakage current increase rapidly. Within these lim- its, the LTC2430 or LTC2431 converts the bipolar differen- tial input signal, V drops CC to +FS = 0.5 • V range the converter indicates the overrange or the underrange condition using distinct output codes. ...
Page 13
... Figure 3. Whenever CS is HIGH, SDO remains high impedance and any externally generated SCK clock pulses are ignored by the internal data out shift register. CS SDO Hi-Z SCK SLEEP Table 2. LTC2430/LTC2431 Output Data Format Differential Input Voltage 0.5 • REF 0.5 • ...
Page 14
... When a fundamental rejection frequency different from 50Hz or 60Hz is required or when the converter must be synchronized with an outside source, the LTC2430 or LTC2431 can operate with an external conversion clock. The converter automatically detects the presence of an external clock signal at the F pin and turns off the internal O oscillator ...
Page 15
... Grounding CS will force the ADC to continuously convert at the maximum output rate selected by F SERIAL INTERFACE TIMING MODES The LTC2430/LTC2431’s 3-wire interface is SPI and MICROWIRE compatible. This interface offers several flexible modes of operation. These include internal/exter- nal serial clock 3-wire I/O, single cycle conversion. ...
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... LTC2430/LTC2431 U U APPLICATIO S I FOR ATIO Table 4. LTC2430/LTC2431 Interface Timing Modes Configuration External SCK, Single Cycle Conversion External SCK, 2-Wire I/O Internal SCK, Single Cycle Conversion Internal SCK, 2-Wire I/O, Continuous Conversion CS TEST EOC TEST EOC SDO Hi-Z Hi-Z SCK (EXTERNAL) CONVERSION SLEEP SLEEP TEST EOC The serial clock mode is selected on the falling edge of CS ...
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... SCK is driven LOW on the falling edge of CS. An internal weak pull-up resistor is active on the SCK pin during the falling edge of CS; therefore, the internal serial clock timing mode is auto- matically selected if SCK is not externally driven. LTC2430/LTC2431 50Hz REJECTION = EXTERNAL OSCILLATOR ...
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... REF – GND BIT 23 BIT 22 BIT 21 BIT 20 EOC SIG MSB DATA OUTPUT Figure 7. External Serial Clock Operation 2. LTC2430/ LTC2431 + REFERENCE REF SCK VOLTAGE – REF 0. ANALOG INPUT RANGE + IN SDO –0.5V TO 0.5V REF REF – GND < ...
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... TO 0.5V REF REF – GND <t EOCtest BIT 23 BIT 22 BIT 21 BIT 20 EOC SIG MSB Hi-Z DATA OUTPUT SLEEP LTC2430/LTC2431 , the first rising EOCtest 50Hz REJECTION = EXTERNAL OSCILLATOR 10k = 60Hz REJECTION 3-WIRE SPI INTERFACE TEST EOC BIT 19 BIT 18 BIT 8 Hi-Z CONVERSION 2431 F09 ...
Page 20
... SCK pin or by never pulling CS HIGH when SCK is LOW. Whenever SCK is LOW, the LTC2430/LTC2431’s internal pull-up at pin SCK is disabled. Normally, SCK is not exter- nally driven if the device is in the internal SCK timing mode. ...
Page 21
... Parallel termination near the LTC2430/LTC2431 pin will eliminate this problem but will increase the driver power dissipation. A series resistor between 27 placed near the driver or near the LTC2431 pin will also eliminate this problem without additional power dissipa- tion. The actual resistor value depends upon the trace impedance and connection topology ...
Page 22
... Driving the Input and Reference The input and reference pins of the converter (LTC2430 or LTC2431) are directly connected to a network of sampling capacitors. Depending upon the relation between the dif- ferential input voltage and the differential reference volt- age, these capacitors are switching between these four pins transfering small amounts of charge in the process ...
Page 23
... C are unavoidably present as IN parasitics of input multiplexers, wires, connectors or sensors, the LTC2430 or LTC2431 can maintain its excep- tional accuracy while operating with relative large values of source resistance as shown in Figures 13 and 14. These measured results may be slightly different from the first ...
Page 24
... LTC2430/LTC2431 U U APPLICATIO S I FOR ATIO The typical +FS and –FS errors as a function of the sum of + the source resistance seen by IN and are shown in Figure 15 addition to this gain error, an offset error term may also appear. The offset error is proportional with the mismatch ...
Page 25
... This current, nominally 1nA ( 10nA max), results in a small offset shift. A 100 source resistance will create a 0.1 V typical and 1 V maximum offset voltage. Reference Current In a similar fashion, the LTC2430 or LTC2431 samples the + differential reference pins REF and REF amount of charge to and from the external driving circuits thus producing a dynamic reference current ...
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... LTC2430/LTC2431 U U APPLICATIO S I FOR ATIO 0 C REF –10 – REF REF – REF –40 V – = GND REF 3.75V IN V – = 1.25V – GND –60 0 100 200 300 400 500 600 700 SOURCE Figure 18a ...
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... IN pins. 3dB frequency. When the internal oscillator is used, the shape of the LTC2430/LTC2431 input bandwidth is shown in Figure 28. When an external oscillator of frequency f is used, the shape of the LTC2430/LTC2431 input EOSC , C ) are used, the ...
Page 28
... LTC2430/LTC2431 U U APPLICATIO S I FOR ATIO INCM REFCM REF EXT OSC OUTPUT DATA RATE (READINGS/SEC) Figure 20. Offset Error vs Output Data Rate and Temperature INCM REFCM ...
Page 29
... noise (referred to the LTC2430/LTC2431 input) can now be obtained by summing as square root of sum of squares the three ADC input referred noise sources: the LTC2430/ LTC2431 internal noise (2.8 V), the noise of the IN driving amplifier and the noise of the IN LTC2430/LTC2431 22 21 ...
Page 30
... LTC2430/LTC2431. If passive RC components are S placed in front of the LTC2430/LTC2431, the input dy- namic current should be considered (see Input Current section). In cases where large effective RC time constants are used, an external buffer amplifier may be required to minimize the effects of dynamic input current. ...
Page 31
... Figure 35. Input Normal Mode Rejection vs Input Frequency LTC2430/LTC2431 have a full-scale differential input range of 5V peak-to-peak. Figures 36 and 37 show measure- ment results for the LTC2430/LTC2431 normal mode re- jection ratio with a 7.5V peak-to-peak (150% of full scale) input signal superimposed over the more traditional nor- mal mode rejection ratio results obtained with a 5V peak- to-peak (full scale) input signal ...
Page 32
... BRIDGE APPLICATIONS Typical strain gauge based bridges deliver only 2mV/Volt of excitation. As the maximum reference voltage of the LTC2430/LTC2431 is 5V, remote sensing of applied exci- tation without additional circuitry requires that excitation be limited to 5V. This gives only 10mV full scale, which can be resolved to 1 part in 3500 without averaging. For many solid state sensors, this is comparable to the sensor ...
Page 33
... The use of a true three amplifier instrumentation amplifier is not necessary, as the LTC2430/ LTC2431 have common mode rejection far beyond that of most amplifiers. The LTC1051 is a dual autozero amplifier that can be used to produce a gain of 10 before its input referred noise dominates the LTC2430/LTC2431 noise ...
Page 34
... U U APPLICATIO S I FOR ATIO practice in earlier generations of load-cell interfaces, how- ever the accuracy of the LTC2430/LTC2431 changes the rationale. Achieving high gain accuracy and linearity at higher gains may prove difficult, while providing little benefit in terms of noise reduction gain of 100, the gain error that could result from typical open-loop gain of 160dB is – ...
Page 35
... APPLICATIO S I FOR ATIO single variable element bridges, the nonlinearity of the half bridge output can be eliminated completely; if the refer- ence arm of the bridge is used as the reference to the ADC, as shown in Figure 41. The LTC2430/LTC2431 can accept inputs Hence, the reference resistor R1 REF must be at least 2 the highest value of the variable resistor ...
Page 36
... LTC1043 FILM 12 200 14 –10V 15V LT1236 0 0 LTC2430/ LTC2431 + REF – REF + IN – IN GND *FLYING CAPACITORS ARE FILM (MKP OR EQUIVALENT) 4 SEE LTC1043 DATA SHEET FOR 7 DETAILS ON UNUSED HALF 2431 F43 17 –10V ...
Page 37
... LTC2430/LTC2431, via an inexpensive multiplexer such as the 74HC4052. Figure 44 shows the use of an LTC2430/LTC2431 with a differential multiplexer. This is an inexpensive multiplexer that will contribute some error due to leakage if used directly with the output from the bridge resistors are inserted as a protection mechanism from overvoltage ...
Page 38
... RN1 10k 10V RN1 10k 4 –5V 8 RN1 10k 15V – 20 1/2 7 LT1112 –15V –15V 5V LT1236 0 LTC2430/ LTC2431 + REF – REF + IN – IN RN1 GND 10k RN1 IS CADDOCK T914 10K-010-02 2431 F45 24301f ...
Page 39
... TYP 0.53 0.01 (.021 .006) 1.10 (.043) DETAIL “A” MAX SEATING PLANE 0.17 – 0.27 (.007 – .011) TYP LTC2430/LTC2431 .189 – .196* (4.801 – 4.978) .009 (0.229 REF .150 – .157** (3.810 – 3.988 .004 – ...
Page 40
... REF – IN GND THE LT1790 IS AVAILABLE WITH 1.25V, 2.048V, 2.5V, 3V, 3.3V, 4.096V AND 5V OUTPUTS THE LTC2431 MAY BE POWERED BY THE LT1790 3V, 3.3V, 4.096V AND 5V VERSIONS COMMENTS 3ppm/ C Drift, 0.05% Max Initial Accuracy 80 A Supply Current, 0.5 C Initial Accuracy No External Components 5 V Offset, 1.6 V 0.05% Max Initial Accuracy, 5ppm/ C Drift ...