Datasheet LTC2440 (Analog Devices) - 10

LTC2440
APPLICATIONS INFORMATION
Initially, the LTC2440 performs a conversion. Once the
Power-Up Sequence
conversion is complete, the device enters the sleep state. The LTC2440 automatically enters an internal reset state While in this sleep state, power consumption is reduced when the power supply voltage V below 10µA. The part remains in the sleep state as long as CC drops below approxi- mately 2.2V. This feature guarantees the integrity of the CS is HIGH. The conversion result is held indefinitely in a conversion result and of the serial interface mode selection. static shift register while the converter is in the sleep state. When the V Once CS is pulled LOW, the device begins outputting the CC voltage rises above this critical threshold, the converter creates an internal power-on-reset (POR) signal conversion result. There is no latency in the conversion with a duration of approximately 0.5ms. The POR signal result. The data output corresponds to the conversion clears all internal registers. Following the POR signal, the just performed. This result is shifted out on the serial data LTC2440 starts a normal conversion cycle and follows the out pin (SDO) under the control of the serial clock (SCK). succession of states described above. The first conversion Data is updated on the falling edge of SCK allowing the result following POR is accurate within the specifications user to reliably latch data on the rising edge of SCK (see of the device if the power supply voltage is restored within Figure 3). The data output state is concluded once 32-bits the operating range (4.5V to 5.5V) before the end of the are read out of the ADC or when CS is brought HIGH. The POR time interval. device automatically initiates a new conversion and the cycle repeats.
Reference Voltage Range
Through timing control of the CS, SCK and EXT pins, This converter accepts a truly differential external reference the LTC2440 offers several flexible modes of operation voltage. The absolute/common mode voltage specification (internal or external SCK). These various modes do not for the REF+ and REF– pins covers the entire range from require programming configuration registers; moreover, GND to VCC. For correct converter operation, the REF+ pin they do not disturb the cyclic operation described above. must always be more positive than the REF– pin. These modes of operation are described in detail in the Serial Interface Timing Modes section. The LTC2440 can accept a differential reference voltage from 0.1V to VCC. The converter output noise is determined
Ease of Use
by the thermal noise of the front-end circuits, and as such, its value in microvolts is nearly constant with reference The LTC2440 data output has no latency, filter settling voltage. A decrease in reference voltage will not signifi- delay or redundant data associated with the conversion cantly improve the converter’s effective resolution. On the cycle. There is a one-to-one correspondence between the other hand, a reduced reference voltage will improve the conversion and the output data. Therefore, multiplexing converter’s overall INL performance. multiple analog voltages is easy. Speed/resolution adjust- ments may be made seamlessly between two conversions
Input Voltage Range
without settling errors. The analog input is truly differential with an absolute/com- The LTC2440 performs offset and full-scale calibrations mon mode range for the IN+ and IN– input pins extending every conversion cycle. This calibration is transparent to from GND – 0.3V to VCC + 0.3V. Outside these limits, the the user and has no effect on the cyclic operation described ESD protection devices begin to turn on and the errors above. The advantage of continuous calibration is extreme due to input leakage current increase rapidly. Within these stability of offset and full-scale readings with respect to limits, the LTC2440 converts the bipolar differential input time, supply voltage change and temperature drift. signal, VIN = IN+ – IN–, from –FS = –0.5 • VREF to +FS = 0.5 • VREF where VREF = REF+ – REF–. Outside this range, 2440fe 10 For more information www.linear.com/LTC2440 Document Outline Features Description Applications Typical Application Absolute Maximum Ratings Pin Configuration Typical Performance Characteristics Pin Functions Typical Application Related Parts