LTC2414 LINER [Linear Technology], LTC2414 Datasheet
LTC2414
Available stocks
Related parts for LTC2414
LTC2414 Summary of contents
Page 1
... INL and 0.2ppm RMS noise. They use delta-sigma technology and provide single cycle settling time for multiplexed applications. Through a single pin, the LTC2414/LTC2418 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
... Consult LTC Marketing for parts specified with wider operating temperature ranges (Notes 1, 2) Operating Temperature Range + 0.3V) LTC2414/LTC2418C ................................ 0°C to 70° 0.3V) LTC2414/LTC2418I ............................ – 40°C to 85° 0.3V) Storage Temperature Range ................. – 65°C to 150° 0.3V) Lead Temperature (Soldering, 10 sec).................. 300° ...
Page 3
... CC – GND (Note 5) – – GND GND – – GND GND (Note 7) – – GND GND (Note 8) LTC2414/LTC2418 MIN TYP MAX UNITS ● 24 Bits 1 ppm of V REF ● ppm of V REF 5 ppm of V REF µV ● 2 nV/° ...
Page 4
... LTC2414/LTC2418 ALOG I PUT A D REFERE CE temperature range, otherwise specifications are at T SYMBOL PARAMETER + IN Absolute/Common Mode IN – IN Absolute/Common Mode IN V Input Differential Voltage Range IN + – (IN – REF Absolute/Common Mode REF – REF Absolute/Common Mode REF V Reference Differential Voltage Range REF + – ...
Page 5
... External Oscillator (Note 11) Internal Oscillator (Note 10) External Oscillator (Notes 10, 11) (Note 10) (Note 9) (Note 9) (Note 9) Internal Oscillator (Notes 10, 12) External Oscillator (Notes 10, 11) LTC2414/LTC2418 ● denotes specifications which apply over the full MIN TYP MAX ● 0.4 ● V – 0.5 CC ● 0.4 ● ...
Page 6
... LTC2414/LTC2418 CHARACTERISTICS range, otherwise specifications are SYMBOL PARAMETER CS ↓ to SDO Low ↑ to SDO High ↓ to SCK ↓ ↓ to SCK ↑ t4 SCK ↓ to SDO Valid t KQMAX SDO Hold After SCK ↓ t KQMIN SCK Set-Up Before CS ↓ ...
Page 7
... V = 2.5V 10 DISTRIBUTION REF –0.48ppm IN σ = 0.375ppm V = 2.5V INCM –2.4 –1.2 –0.6 0 0.6 1.2 –1.8 OUTPUT CODE (ppm REF 241418 G08 LTC2414/LTC2418 Total Unadjusted Error (V = 2.7V 2.5V) CC REF GND –45° 2. 2.5V REF 1.25V INCM REFCM 85° ...
Page 8
... LTC2414/LTC2418 W U TYPICAL PERFOR A CE CHARACTERISTICS RMS Noise vs Input Differential Voltage 0 GND 25° 0 REF V = 2.5V INCM 0.3 0.2 0.1 0 –2.5 –2.0 –1.5 –1.0 –0.5 0 0.5 1.0 1.5 2.0 2.5 INPUT DIFFERENTIAL VOLTAGE (V) 241418 G10 RMS Noise 1.0 0.9 0.8 0 GND 25° 0 GND INCM + REF = 2.5V – ...
Page 9
... SDI = GND 600 T = 25° 500 REF CC 400 300 200 100 100 OUTPUT DATA RATE (READINGS/SEC) 241418 G26 LTC2414/LTC2418 Full-Scale Error vs V REF +FS ERROR 1 0 –1 –FS ERROR – GND 25°C A –3 V ...
Page 10
... PI FU CTIO S CH0 to CH15 (Pin 21 to Pin 28 and Pin 1 to Pin 8): Analog Inputs. May be programmed for single-ended or differen- tial mode. CH8 to CH15 (Pin 1 to Pin 8) not connected on the LTC2414. V (Pin 9): Positive Supply Voltage. Bypass to GND CC (Pin 15) with a 10µF tantalum capacitor in parallel with 0.1µ ...
Page 11
... Figure 2). The 4-wire interface consists of serial data input (SDI), serial data out- put (SDO), serial clock (SCK) and chip select (CS). Initially, the LTC2414 or LTC2418 performs a conversion. Once the conversion is complete, the device enters the sleep state. The part remains in the sleep state as long as ...
Page 12
... LTC2418 achieve a minimum of 110dB rejection at the line frequency (50Hz or 60Hz ±2%). Ease of Use The LTC2414/LTC2418 data output has no latency, filter settling delay or redundant data associated with the conversion cycle. There is a one-to-one correspondence between the conversion and the output data. Therefore, multiplexing multiple analog voltages is easy ...
Page 13
... LTC2414 or one of the 16 channels (CH0-CH15) for the LTC2418 is selected as the positive input and the COM pin is used as the negative input. For the LTC2414, the lower half channels (CH0-CH7) are used and the channel ad- dress bit A2 should be always 0, see Table 1. While for the ...
Page 14
... SIG MSB Hi-Z SCK SDI SGL SLEEP CONVERSION RESULT N – 1 SDO ADDRESS N – 1 SCK SDI ADDRESS N OUTPUT OPERATION N – 1 Table 1. Channel Selection for the LTC2414 (Bit A2 Should Always Be 0) MUX ADDRESS ODD/ SGL SIGN * ...
Page 15
... Output Data Format The LTC2414/LTC2418 serial output data stream is 32 bits long. The first 3 bits represent status information indicat- ing the sign and conversion state. The next 23 bits are the conversion result, MSB first. The next 5 bits (Bit 5 to Bit 1) ...
Page 16
... DMY SIG MSB Frequency Rejection Selection ( The LTC2414/LTC2418 internal oscillator provides better than 110dB normal mode rejection at the line frequency and all its harmonics for 50Hz ±2% or 60Hz ±2%. For 60Hz rejection, F 50Hz rejection the F ...
Page 17
... V When a fundamental rejection frequency different from 50Hz or 60Hz is required or when the converter must be synchronized with an outside source, the LTC2414/ LTC2418 can operate with an external conversion clock. The converter automatically detects the presence of an external clock signal at the F ...
Page 18
... SDI pin on the rising edge of the serial clock. In the Internal SCK mode of operation, the SCK pin is an output and the LTC2414/LTC2418 create their own serial clock by dividing the internal conversion clock the External SCK mode of operation, the SCK pin is used as input ...
Page 19
... Grounding CS will force the ADC to continuously convert at the maximum output rate selected by F SERIAL INTERFACE TIMING MODES The LTC2414/LTC2418’s 4-wire interface is SPI and MICROWIRE compatible. This interface offers several flexible modes of operation. These include internal/exter- Table 6. LTC2414/LTC2418 Interface Timing Modes ...
Page 20
... HIGH, the address information is discarded and the previ- ous address is kept. This is useful for systems not requir- ing all 32 bits of output data, aborting an invalid conversion cycle or synchronizing the start of a conversion. 2.7V TO 5.5V 1µ LTC2414/ LTC2418 REFERENCE REF SDI VOLTAGE 12 18 – ...
Page 21
... BIT 29 BIT 28 BIT 27 BIT 26 BIT 25 SIG MSB ODD/ (0) EN SGL A2 A1 SIGN DATA OUTPUT Figure 7. External Serial Clock Operation LTC2414/LTC2418 50Hz REJECTION = EXTERNAL OSCILLATOR = 60Hz REJECTION 3-WIRE SPI INTERFACE BIT 24 BIT 6 BIT 0 LSB PARITY A0 DON’T CARE CONVERSION 241418 F07 ...
Page 22
... SDO pin on each falling edge of SCK. The internally generated serial clock is output to the SCK pin. This signal may 2.7V TO 5.5V 1µ LTC2414/ LTC2418 REFERENCE REF SDI VOLTAGE 12 18 – REF SCK ...
Page 23
... SLEEP SLEEP Figure 9. Internal Serial Clock, Reduced Data Output Length Whenever SCK is LOW, the LTC2414/LTC2418’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. However, certain applications may require an external driver on SCK. If this driver goes Hi-Z after outputting a LOW signal, the LTC2414/LTC2418’ ...
Page 24
... SDO goes HIGH (EOC = 1) indicating a new conversion is in progress. SCK remains HIGH during the conversion. PRESERVING THE CONVERTER ACCURACY The LTC2414/LTC2418 are designed to reduce as much as possible the conversion result sensitivity to device decoupling, PCB layout, antialiasing circuits, line fre- 24 ...
Page 25
... Undershoot and overshoot can occur because of the impedance mismatch at the converter pin when the transition time of an external control signal is less than twice the propagation delay from the driver to LTC2414/ LTC2418. For reference regular FR-4 board, signal propagation velocity is approximately 183ps/inch for internal traces and 170ps/inch for surface traces ...
Page 26
... SWITCHING FREQUENCY f = 76800Hz INTERNAL OSCILLATOR ( 0.5 • f EXTERNAL OSCILLATOR SW EOSC Figure 11. LTC2414/LTC2418 Equivalent Analog Input Circuit source impedance result in only small errors. Such values for C will deteriorate the converter offset and gain IN performance without significant benefits of signal filtering and the user is advised to avoid them. Nevertheless, when ...
Page 27
... IN for common mode input signal into a differential mode input signal of 0.23ppm. When F oscillator with a frequency f source impedance transforms a full-scale common mode input signal into a differential mode input signal of LTC2414/LTC2418 + IN LTC2414/ LTC2418 – IN 2414/18 F12 – REF = 5V – ...
Page 28
... A 100Ω source resistance will create a 0.1µV typical and 1µV maximum offset voltage. Reference Current In a similar fashion, the LTC2414/LTC2418 samples the differential reference pins REF small amount of charge to and from the external driving circuits thus producing a dynamic reference current. This current does not change the converter offset, but it may degrade the gain and INL performance ...
Page 29
... REF (Small C ) Figure 19. –FS Error 0.01µF = 0.1µF 2414/18 F20 + – and REF (Large C ) Figure 21. –FS Error vs R REF LTC2414/LTC2418 + – or REF . When F is driven (external conver- EOSC Ω and each ohm of source 12 /f EOSC + – or REF will result in • ...
Page 30
... C REF mum full-scale error. Output Data Rate + When using its internal oscillator, the LTC2414/LTC2418 can produce up to 7.5 readings per second with a notch frequency of 60Hz (F – pins rather than to second with a notch frequency of 50Hz (F ...
Page 31
... If small external input and/ EOSC or reference capacitors ( are used, the effect of IN REF the external source resistance upon the LTC2414/LTC2418 typical performance can be inferred from Figures 12, 13, 18 and 19 in which the horizontal axis is scaled by 153600 EOSC Third, an increase in the frequency of the external oscilla- tor above 460800Hz (a more than 3× ...
Page 32
... Due to the complex filtering and calibration algorithms utilized, the converter input bandwidth is not modeled very accurately by a first order filter with the pole located at the 3dB frequency. When the internal oscillator is used, the shape of the LTC2414/LTC2418 input bandwidth is shown in Figure 31 for F = LOW and F = HIGH. When an external ...
Page 33
... noise (referred to the LTC2414/LTC2418 input) can now be obtained by summing as square root of sum of squares the three ADC input referred noise sources: the LTC2414/ LTC2418 internal noise (1µV), the noise of the IN – amplifier and the noise of the IN driving amplifier. ...
Page 34
... As a result of these remarkable normal mode specifica- represents the N tions, minimal (if any) antialias filtering is required in front of the LTC2414/LTC2418. If passive RC components are placed in front of the LTC2414/LTC2418, the input dy- value. N 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 35
... In Figure 39, the LTC2414/LTC2418 uses the internal oscillator with the notch set at 60Hz (F and in Figure 40 it uses the internal oscillator with the ...
Page 36
... ADC, or can be digitized via multiple ADC channels and summed mathematically. The mathematical summation of the output of multiple LTC2414/LTC2418’s provides the benefit of a root square reduction in noise. The low power consumption of the LTC2414/LTC2418 makes it attractive for multidrop communication schemes where the ADC is located within the load-cell housing ...
Page 37
... This example produces a differen- tial output with a common mode voltage of 2.5V, as determined by the bridge. The use of a true three amplifier instrumentation amplifier is not necessary, as the LTC2414/ LTC2418 has 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 15 before its input referred noise dominates the LTC2414/LTC2418 noise ...
Page 38
... ADC, as shown in Figure 44. The LTC2414/LTC2418 can accept inputs up to 1/2 V must be at least 2x the highest value of the variable resistor. ...
Page 39
... R2 10k + 0.1% R3 1µF R1 10k LTC1050 10k – LTC2414/LTC2418 REF 560Ω 12 – REF LTC2414/ LTC2418 10k 21 CH0 10k 22 CH1 GND 15 2410 F51 39 241418fa ...
Page 40
... Figure 46. LTC1043 Provides Precise 4X Reference for Excitation Voltages configured to provide 10V and –5V excitation to the bridge, producing a common mode voltage at the input to the LTC2414/LTC2418 of 2.5V, maximizing the AC input range for applications where induced 60Hz could reach amplitudes 15V U1 15V ...
Page 41
... Figure 47. Use Resistor Arrays to Provide Precise Matching in Excitation Amplifier MULTIPLE CHANNEL USAGE The LTC2414/LTC2418 have up to sixteen input channels and this feature provides a very flexible and efficient solution in applications where more than one variable need to be measured. Measurements of a Ladder of Sensors ...
Page 42
... LTC2414/LTC2418 and a PIC16F84 microcontroller. The sample program for CC5X compiler in Figure 50 can be used to program the PIC16F84 to control the LTC2414/ LTC2418. It uses PORT B to interface with the device. The program begins by declaring variables and allocating four memory locations to store the 32-bit conversion result ...
Page 43
... Conversion result LS byte // function prototype // no interrupts // all PORTA pins outputs // according to definitions above // next channel to send // CH0,1 DIFF. // activate ADC // test for end of conversion // read ADC, send next channel // deactivate ADC Figure 50. Sample Program in CC5X for PIC16F84 LTC2414/LTC2418 241418fa 43 ...
Page 44
... LTC2414/LTC2418 U U APPLICATIO S I FOR ATIO ////////// Bidirectional Shift Routine for ADC ////////// void shiftbidir(char nextch) { int i; for(i=0;i<2;i++) { sdi=nextch.7; nextch = rl(nextch); sck=1; sck=0; } for(i=0;i<8;i++) { sdi=nextch.7; nextch = rl(nextch); result_3 = rl(result_3);// get ready to load lsb result_3.0 = sdo; sck=1; sck=0; } for(i=0;i<8;i++) { result_2 = rl(result_2);// get ready to load lsb result_2.0 = sdo ...
Page 45
... CH12 CH13 CH14 NC CLK CH15 GND INH 1 V SH/LD CC COM 10 Figure 51. Demo Board Schematic LTC2414/LTC2418 D1 BAV74LT1 U2 LT1236ACN8-5 R1 10Ω OUT GND 100µF 16V U3E U3F R3 74HC14 51k U3B U3A R4 74HC14 51k U3C U3D R6 ...
Page 46
... LTC2414/LTC2418 U U APPLICATIO S I FOR ATIO Top Silkscreen Figure 52. LTC2418 Demo Program Display Top Layer Figure 53. PCB Layout and Film Bottom Layer 241418fa ...
Page 47
... TYP 0.008 – 0.012 (0.203 – 0.305) LTC2414/LTC2418 0.386 – 0.393* 0.033 (9.804 – 9.982) (0.838 ...
Page 48
... LTC2414/LTC2418 U TYPICAL APPLICATIO THERMISTOR Figure 54. Multichannel Bridge Digitizer and Digital Cold Junction Compensation RELATED PARTS PART NUMBER DESCRIPTION LT1019 Precision Bandgap Reference, 2.5V, 5V LT1025 Micropower Thermocouple Cold Junction Compensator LTC1050 Precision Chopper Stabilized Op Amp LT1236A-5 Precision Bandgap Reference, 5V LT1460 Micropower Series Reference 24-Bit, No Latency ∆ ...