LTC2485 LINER [Linear Technology], LTC2485 Datasheet
LTC2485
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LTC2485 Summary of contents
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... The LTC2485 allows a wide common mode input range ( reference can be as low as 100mV or can be tied directly to V ...
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... Digital Input Voltage to GND ........ – 0. Digital Output Voltage to GND ..... – 0. Operating Temperature Range LTC2485C ................................................... 0°C to 70°C LTC2485I ................................................ – 40°C to 85°C Storage Temperature Range ................ – 65°C to 125°C ELECTRICAL CHARACTERISTICS ( OR AL SPEED) apply over the full operating temperature range, otherwise specifications are at T ...
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... A CONDITIONS + Voltage – Voltage + – – – – – – REF ) LTC2485 ● denotes the specifications which apply over the MIN TYP MAX ● 24 ● ● 0.5 2 100 ● 25 0.1 ● ...
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... LTC2485 ALOG I PUT A D REFERE CE temperature range, otherwise specifications are at T SYMBOL PARAMETER + + C ( Sampling Capacitance S – – Sampling Capacitance Sampling Capacitance S REF REF + + I ( Leakage Current DC_LEAK – – Leakage Current DC_LEAK + – ...
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... Note 11: The converter uses the internal oscillator. Note 12: The output noise includes the contribution of the internal calibration operations. Note 13: Guaranteed by design and test correlation. Note 14 Note 15: All values refer to V LTC2485 MIN TYP MAX ● 10 4000 ● ...
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... LTC2485 W U TYPICAL PERFOR A CE CHARACTERISTICS Integral Nonlinearity ( 5V) CC REF REF 2.5V IN(CM) 1 –45°C 25°C 0 85°C –1 –2 –3 –2.5 –2 –1.5 –1 –0.5 0 0.5 1 1.5 2 2.5 INPUT VOLTAGE (V) 2485 G01 Total Unadjusted Error ( 5V) CC REF ...
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... Offset Error 0.3 + REF = 2.5V – REF = GND 0 GND IN(CM 25°C A 0.1 0 –0.1 –0.2 –0.3 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 V (V) CC 2485 G17 LTC2485 RMS Noise vs Temperature ( 1 REF 0 GND IN(CM) 0.8 0.7 0.6 0.5 0.4 – –30 –15 15 TEMPERATURE (°C) 2485 G12 Offset Error vs V IN(CM) ...
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... LTC2485 W U TYPICAL PERFOR A CE CHARACTERISTICS Temperature Sensor vs Temperature 0. 1.4V REF 0.35 0.30 0.25 0.20 –60 – 120 TEMPERATURE (°C) 2485 G19 On-Chip Oscillator Frequency 310 V = 2.5V REF GND IN(CM) 308 306 304 302 300 2.5 3.0 3.5 4.0 4.5 5.0 5.5 V (V) CC 2485 G22 PSRR vs Frequency 4.1V DC ± ...
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... OUTPUT READING (µV) IN(CM) 240 230 220 210 200 190 180 170 160 (V) 2485 G34 LTC2485 Integral Nonlinearity (2x Speed Mode 5V 2.5V) CC REF 2.5V REF 1.25V IN(CM) 1 90°C 0 –1 –45°C, 25°C –2 – ...
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... LTC2485 W U TYPICAL PERFOR A CE CHARACTERISTICS Offset Error (2x Speed Mode) 250 V = 2.5V REF GND IN(CM) 200 T = 25°C A 150 100 50 0 2.7 3 3 (V) CC 2485 G36 PSRR vs Frequency at V (2x Speed Mode 4.1V DC ±1. REF = 2.5V –20 – REF = GND ...
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... SCL (Pin 6): Serial Clock Pin of the I LTC2485 can only act as a slave and the SCL pin only accepts external serial clock. Data is shifted into the SDA pin on the rising edges of the SCL clock and output through the SDA pin on the falling edges of the SCL clock ...
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... At the same time any device addressed is considered a slave. The LTC2485 can only be addressed as a slave. Once addressed, it can receive configuration bits or transmit the last conversion result. Therefore the serial clock line SCL is an input only and the data line SDA is bidirectional ...
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... Acknowledge (ACK) by pulling SDA LOW or leaves SDA HIGH to indicate a Not Acknowledge (NAK) condition. Change of data state can only happen while SCL is LOW. t SU;DAT SU;STA t Sr HIGH LTC2485 2 C bus is busy and data groups of nine bits (one byte HD;STA SP r BUF t SU ...
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... These special features are selected through a single 8-bit serial input word during the data input/out- put cycle (see Figure 3). The LTC2485 powers default mode commonly used for most measurements. The device will remain in this mode until a valid write cycle is performed. In this ...
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... When the LTC2485 is addressed for a Read operation, it acknowledges (by pulling SDA LOW) and acts as a transmitter. The master and receiver can read up to four bytes from the LTC2485. After a complete Read operation (4 bytes), the output register is emptied, a new conversion is initiated, and a following Read request in the same output phase will be NAKed ...
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... ACK/NAK cycle). LTC2485 Address – and IN pins is main- The LTC2485 has two address pins, enabling one in 6 possible addresses, as shown in Table 4. to Table 4. LTC2485 Address Assignment REF CA1 ...
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... At the conclusion of the conversion cycle, the next result may be read using the method described above. If the conversion cycle is not con- cluded and a valid address selects the device, the LTC2485 generates a NAK signal indicating the conversion cycle is in progress. Continuous Read/Write ...
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... Figure 8. Start a New Conversion without Reading Old Conversion Result SCL SDA LTC2485 S GLOBAL ADDRESS ALL LTC2485s IN SLEEP Figure 9. Synchronize the LTC2485s with the Global Address Call Easy Drive Input Current Cancellation The LTC2485 combines a high precision delta-sigma ADC with an automatic differential input current cancellation front end ...
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... CA0/F may be tied HIGH or left floating in order to set the 0 ) chip address. The LTC2485 operation will not be dis- 0 turbed if the change of conversion clock source occurs during the sleep state or during the data output state while the converter uses an external serial clock. If the change ...
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... The POR signal clears all internal registers. Following the POR signal, the LTC2485 starts a normal conversion cycle and follows the succession of states described in Figure 1. The first conversion result following POR is accurate within the specifications of the device if the power supply voltage is restored within the operating range (2 ...
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... Driving the Input and Reference + – and IN input pins The input and reference pins of the LTC2485 converter are + 0.3V. Outside CC directly connected to a network of sampling capacitors. Depending upon the relation between the differential input voltage and the differential reference voltage, these capaci- – ...
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... For the case of balanced input impedances, the common mode input current effects are rejected by the large CMRR of the LTC2485 leading to little degradation in accuracy. Mismatches in source impedances lead to gain errors proportional to the difference between the common mode input voltage and the common mode reference voltage. 1% mismatches in 1kΩ ...
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... U U APPLICATIO S I FOR ATIO voltage). Table 6 summarizes the effects of mismatched source impedance and differences in reference/input com- mon mode voltages. Table 6. Suggested Input Configuration for LTC2485 BALANCED INPUT RESISTANCES Constant C > 1nF at Both EXT + – V – and IN . Can Take IN(CM) REF(CM) Large Source Resistance Source Resistance ...
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... LTC2485 U U APPLICATIO S I FOR ATIO Reference Current In a similar fashion, the LTC2485 samples the differential + – reference pins REF and REF transferring 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 ...
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... When oper- ated with an external conversion clock (CA0 external oscillator), the LTC2485 output data rate can be increased as desired. The duration of the conversion 10 0 – ...
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... OUTPUT DATA RATE (READINGS/SEC) Figure 21. Offset Error vs Output Data Rate and Temperature effect of the external source resistance upon the LTC2485 typical performance can be inferred from Figures 14, 15, 16 and 17 in which the horizontal axis is scaled by 307200/f Third, an increase in the frequency of the external oscillator ...
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... OUTPUT DATA RATE (READINGS/SEC) Figure 27. Resolution (Noise vs Output Data Rate and Reference Voltage 25° 100 2485 F23 90 100 80 2485 F25 ≤ 1LSB) MAX = 5V REF 90 100 80 2485 F27 ≤ 1LSB) RMS LTC2485 25° 85° IN(CM) REF(CM ...
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... When external amplifiers are driving the LTC2485, the ADC input referred system noise calculation can be simplified by Figure 30. The noise of an amplifier driving the LTC2485 input pin can be modeled as a band limited white noise source. Its bandwidth can be approximated by the bandwidth of a single pole lowpass filter with a corner frequency f ...
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... 2485 F31 EOSC/5120 2485 F33 Figure 34. Input Normal Mode Rejection at f LTC2485 100 60Hz MODE 10 50Hz MODE 1 0.1 0 100 1k 10k 100k INPUT NOISE SOURCE SINGLE POLE EQUIVALENT BANDWIDTH (Hz) 2485 F30 0 –10 –20 –30 –40 – ...
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... As a result of these remarkable normal mode specifica- tions, minimal (if any) antialias filtering is required in front of the LTC2485. If passive RC components are placed in front of the LTC2485, the input dynamic current should be considered (see Input Current section). In this case, the differential input current cancellation feature of the LTC2485 allows external RC networks without significant degrada- tion in DC performance ...
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... IN(P-P) (150% OF FULL SCALE) 0 12.5 25 37.5 50 62.5 75 87.5 100 112.5 125 137.5 150 162.5 175 187.5 200 INPUT FREQUENCY (Hz) Figure 39. Measured Input Normal Mode Rejection vs Input Frequency with Input Perturbation of 150% Full Scale (50Hz Notch) LTC2485 MEASURED DATA CALCULATED DATA INPUT FREQUENCY (Hz IN(P- 7.5V ...
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... Typical measured values of the normal mode rejection of the LTC2485 operating with the internal oscil- lator and 2x speed mode is shown in Figure 42. When the LTC2485 is configured in 2x speed mode, by performing a running average, a SINC 4 with the SINC digital filter, yielding the normal mode rejection identical as that for the 1x speed mode ...
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... REF LTC2485 R8 – REF TYPE K THERMOCOUPLE JACK (OMEGA MPJ-K-F) 26.3C Figure 44. Calibration Setup LTC2485 0 –20 –40 –60 –80 –100 –120 248 250 252 254 256 258 260 262 264 INPUT SIGNAL FREQUENCY ( 2485 F41 –70 –80 NO AVERAGE –90 WITH – ...
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... READ 0x01 #define WRITE 0x00 #define LTC248XADDR 0b01001000 // Useful defines for the LTC2481 and LTC2485 - OR them together to make the // 8 bit config word. // These do NOT apply to the LTC2483. // Select gain - 1 to 256 (also depends on speed setting) // Does NOT apply to LTC2485. #define GAIN1 ...
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... Linear Technonlgy Corporation June 23, 2005 Written for CCS PCM compiler, Version 3.182 */ #include “LTC248X.h” /*** read_LTC2485() ************************************************************ This is the funciton that actually does all the work of talking to the LTC2485. Arguments: addr - device address config - configuration bits for next conversion Returns: zero if conversion is in progress, 32 bit signed integer LTC2485 output word ...
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... LTC2485 U U APPLICATIO S I FOR ATIO *******************************************************************************/ signed int32 read_LTC2485(char addr, char config) { struct fourbytes // Define structure of four consecutive bytes { // To allow byte access bit int or float. int8 te0; // int8 te1; // The make32() function in this compiler will int8 te2; // also work, but a union of 4 bytes and a 32 bit int int8 te3 ...
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... Pace the main loop to something more than This is a basic error detection scheme. The LTC2485 will never take more than // 163.5ms, 149.9ms, or 136.5ms to complete a conversion in the 50Hz, 55Hz, and 60Hz // rejection modes, respectively read_LTC2485() does not return non-zero within this time period, something // is wrong, such as an incorrect i2c address or bus conflict ...
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... LTC2485 PACKAGE DESCRIPTIO 3.50 ±0.05 1.65 ±0.05 2.15 ±0.05 (2 SIDES) 0.25 ± 0.05 RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS PIN 1 TOP MARK (SEE NOTE 6) 0.200 REF Package 10-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1698) 0.675 ±0.05 PACKAGE OUTLINE 0.50 BSC 2.38 ±0.05 (2 SIDES) 3.00 ±0.10 1.65 ± ...
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... REF × 16 CHARACTER D5 LCD DISPLAY D4 (OPTREX DMC162488 EN OR SIMILAR GND CALIBRATE 10k 2 1 DOWN Figure 45. Complete Type K Thermocouple Meter LTC2485 PIC16F73 20 18 RC7 RC6 16 1.7k 1.7k RC5 15 RC4 14 Y1 RC3 9 6MHz 13 OSC1 RC2 12 RC1 10 11 ...
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... Noise, 2ppm INL, 3ppm Total Unadjusted Errors 200µA 3.5kHz Output Rate, 200nV Noise, 24.6 ENOBs Pin Compatible with LTC2482/LTC2484 Pin Compatible with LTC2483/LTC2485 Pin Compatible with LTC2480/LTC2484 2 C Interface Pin Compatible with LTC2481/LTC2485 Pin Compatible with LTC2480/LTC2482 www.linear.com ● Noise, 2ppm INL Noise, 4ppm INL, RMS ...