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LTC2444 Datasheet(PDF) 8 Page - Linear Technology |
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LTC2444 Datasheet(HTML) 8 Page - Linear Technology |
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8 / 28 page  LTC2444/LTC2445/ LTC2448/LTC2449 8 sn2444589 2444589fs Initially, the LTC2444/LTC2445/LTC2448/LTC2449 per- form a conversion. Once the conversion is complete, the device enters the sleep state. While in this sleep state, power consumption is reduced below 10µA. The part remains in the sleep state as long as CS is HIGH. The conversion result is held indefinitely in a static shift register while the converter is in the sleep state. Once CS is pulled LOW, the device begins outputting the conversion result. There is no latency in the conversion result while operating in the 1x mode. The data output cor- responds to the conversion just performed. This result is shifted out on the serial data out pin (SDO) under the con- trol of the serial clock (SCK). Data is updated on the falling edge of SCK allowing the user to reliably latch data on the rising edge of SCK (see Figure 3). The data output state is concluded once 32 bits are read out of the ADC or when CS is brought HIGH. The device automatically initiates a new conversion and the cycle repeats. Through timing control of the CS, SCK and EXT pins, the LTC2444/LTC2445/LTC2448/LTC2449 offer several flex- ible modes of operation (internal or external SCK). These various modes do not require programming configuration registers; moreover, they do not disturb the cyclic opera- tion described above. These modes of operation are described in detail in the Serial Interface Timing Modes section. Ease of Use The LTC2444/LTC2445/LTC2448/LTC2449 data output has no latency, filter settling delay or redundant data associated with the conversion cycle while operating in the 1X mode. There is a one-to-one correspondence between the conversion and the output data. Therefore, multiplexing multiple analog voltages is easy. Speed/ resolution adjustments may be made seamlessly be- tween two conversions without settling errors. The LTC2444/LTC2445/LTC2448/LTC2449 perform off- set and full-scale calibrations every conversion cycle. This calibration is transparent to the user and has no effect on the cyclic operation described above. The advantage of continuous calibration is extreme stability of offset and full-scale readings with respect to time, supply voltage change and temperature drift. APPLICATIO S I FOR ATIO Power-Up Sequence The LTC2444/LTC2445/LTC2448/LTC2449 automatically enter an internal reset state when the power supply voltage VCC drops below approximately 2.2V. This fea- ture guarantees the integrity of the conversion result and of the serial interface mode selection. When the VCC voltage rises above this critical threshold, the converter creates an internal power-on-reset (POR) signal with a duration of approximately 0.5ms. The POR signal clears all internal registers. The conversion imme- diately following a POR is performed on the input channel IN+ = CH0, IN– = CH1 at an OSR = 256 in the 1X mode. Following the POR signal, the LTC2444/LTC2445/LTC2448/ LTC2449 start a normal conversion cycle and follow the succession of states described above. The first conver- sion result following POR is accurate within the specifica- tions of the device if the power supply voltage is restored within the operating range (4.5V to 5.5V) before the end of the POR time interval. Reference Voltage Range These converters accept a truly differential external refer- ence voltage. The absolute/common mode voltage speci- fication for the REF+ and REF– pins covers the entire range from GND to VCC. For correct converter operation, the REF+ pin must always be more positive than the REF– pin. The LTC2444/LTC2445/LTC2448/LTC2449 can accept a differential reference voltage from 0.1V to VCC. The con- verter output noise is determined by the thermal noise of the front-end circuits, and as such, its value in microvolts is nearly constant with reference voltage. A decrease in reference voltage will not significantly improve the converter’s effective resolution. On the other hand, a reduced reference voltage will improve the converter’s overall INL performance. Input Voltage Range The analog input is truly differential with an absolute/ common mode range for the CH0-CH15 and COM input pins extending from GND – 0.3V to VCC + 0.3V. Outside these limits, the ESD protection devices begin to turn on and the errors due to input leakage current increase rapidly. Within these limits, the LTC2444/LTC2445/ |
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Similar Description - LTC2444 |
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