Datasheet LTC2444, LTC2445, LTC2448, LTC2449 (Analog Devices) - 10

LTC2444/LTC2445/ LTC2448/LTC2449
applicaTions inForMaTion
clears all internal registers. The conversion immediately
Input Voltage Range
following a POR is performed on the input channel IN+ Refer to Figure 4. The analog input is truly differential with an = CH0, IN– = CH1 at an OSR = 256 in the 1X mode. Fol- absolute/common mode range for the CH0 to CH15 and COM lowing the POR signal, the LTC2444/LTC2445/LTC2448/ input pins extending from GND – 0.3V to V LTC2449 start a normal conversion cycle and follow the CC + 0.3V. Outside these limits, the ESD protection devices begin to turn on succession of states described above. The first conversion and the errors due to input leakage current increase rap- result following POR is accurate within the specifications idly. Within these limits, the LTC2444/LTC2445/LTC2448/ of the device if the power supply voltage is restored within LTC2449 convert the bipolar differential input signal, V the operating range (4.5V to 5.5V) before the end of the IN = IN+ – IN – (where IN+ and IN– are the selected input chan- POR time interval. nels), from –FS = –0.5 • VREF to +FS = 0.5 • VREF where V
Reference Voltage Range
REF = REF+ – REF–. Outside this range, the converter indicates the overrange or the underrange condition using These converters accept a truly differential external distinct output codes. reference voltage. The absolute/common mode voltage specification for the REF+ and REF– pins covers the entire
MUXOUT/ADCIN
range from GND to VCC. For correct converter operation, the There are two differences between the LTC2444/LTC2448 REF+ pin must always be more positive than the REF– pin. and the LTC2445/LTC2449. The first is the RMS noise The LTC2444/LTC2445/LTC2448/LTC2449 can accept a performance. For a given OSR, the LTC2445/LTC2449 differential reference voltage from 0.1V to V noise level is approximately √2 times lower (0.5 effective CC. The con- verter output noise is determined by the thermal noise of bits)than that of the LTC2444/LTC2448. the front-end circuits, and as such, its value in microvolts The second difference is the LTC2445/LTC2449 includes is nearly constant with reference voltage. A decrease in MUXOUT/ADCIN pins. These pins enable an external buf- reference voltage will not significantly improve the con- fer or gain block to be inserted between the output of the verter’s effective resolution. On the other hand, a reduced multiplexer and the input to the ADC. Since the buffer is reference voltage will improve the converter’s overall INL driven by the output of the multiplexer, only one circuit is performance. CS 1 2 3 4 5 6 7 8 9 10 11 12 13 14 32 SCK SDI 1 0 EN SGL ODD A2 A1 A0 OSR3 OSR2 OSR1 OSR0 TWOX BIT 31 BIT 30 BIT 29 BIT 28 BIT 27 BIT 26 BIT 25 BIT 24 BIT 23 BIT 22 BIT 21 BIT 20 BIT 19 BIT 0 Hi-Z Hi-Z SDO EOC “0” SIG MSB LSB BUSY 2444589 F03
Figure 3. SDI Speed/Resolution, Channel Selection, and Data Output Timing
2444589fc 10 For more information www.linear.com/LTC2444 Document Outline Features Description Applications Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Analog Input and Reference Digital Inputs and Digital Outputs Power Requirements Timing Characteristics Pin Functions Functional Block Diagram Test Circuit Applications Information Package Description Revision History Typical Application Related Parts