Datasheet LTC2450 (Analog Devices) - 8

LTC2450
APPLICATIONS INFORMATION Ease of Use
this range. Thus the converter resolution remains at 1LSB independent of the reference voltage. INL, offset, and full- The LTC2450 data output has no latency, fi lter settling delay scale errors vary with the reference voltage as indicated or redundant results associated with the conversion cycle. by the Typical Performance Characteristics graphs. These There is a one-to-one correspondence between the conver- error terms will decrease with an increase in the reference sion and the output data. Therefore, multiplexing multiple voltage (as the LSB size in μV increases). analog input voltages requires no special actions. The LTC2450 performs offset and full-scale calibrations
Input Voltage Range
every conversion. This calibration is transparent to the The ADC is capable of digitizing true rail-to-rail input sig- user and has no effect upon the cyclic operation described nals. Ignoring offset and full-scale errors, the converter previously. The advantage of continuous calibration is will theoretically output an “all zero” digital result when the extreme stability of the ADC performance with respect to input is at ground (a zero scale input) and an “all one” digital time and temperature. result when the input is at VCC (a full-scale input). The LTC2450 includes a proprietary input sampling scheme The converter offset and gain error specifi cations ensure that reduces the average input current several orders of that all 65536 possible codes will be produced within this magnitude as compared to traditional delta sigma archi- voltage range. In an under-range condition, for all input tectures. This allows external fi lter networks to interface voltages less than the voltage corresponding to output directly to the LTC2450. Since the average input sampling code 0, the converter will generate the output code 0. current is 50nA, an external RC lowpass fi lter using a 1kΩ In an over-range condition, for all input voltages greater and 0.1μF results in <1LSB error. than the voltage corresponding to output code 65535 the converter will generate the output code 65535.
Reference Voltage Range Output Data Format
The converter uses the power supply voltage (VCC) as the positive reference voltage (see Figure 1). Thus, the refer- The LTC2450 generates a 16-bit direct binary encoded ence range is the same as the power supply range, which result. It is provided, MSB fi rst, as a 16-bit serial stream extends from 2.7V to 5.5V. The LTC2450’s internal noise through the SDO output pin under the control of the SCK level is extremely low so the output peak-to-peak noise input pin (see Figure 3). remains well below 1LSB for any reference voltage within t3 t t 1 2 CS D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D D 1 0 SDO MSB LSB SCK 2450 F02 tKQ tlSCK thSCK
Figure 3. Data Output Timing
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