LTC2450 datasheet(8/20 Pages) LINER

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LTC2450

2450fa

applications inForMation

this range. Thus the converter resolution remains at 1LSB

independent of the reference voltage. INL, offset, and full-

scale errors vary with the reference voltage as indicated

by the Typical Performance Characteristics graphs. These

error terms will decrease with an increase in the reference

voltage (as the LSB size in µV increases).

Input Voltage Range

The ADC is capable of digitizing true rail-to-rail input sig-

nals. Ignoring offset and full-scale errors, the converter

will theoretically output an “all zero” digital result when the

inputisatground(azeroscaleinput)andan“allone”digital

result when the input is at VCC (a full-scale input).

The converter offset and gain error specifications ensure

that all 65536 possible codes will be produced within this

voltage range. In an under-range condition, for all input

voltages less than the voltage corresponding to output

code 0, the converter will generate the output code 0.

In an over-range condition, for all input voltages greater

than the voltage corresponding to output code 65535 the

converter will generate the output code 65535.

Output Data Format

The LTC2450 generates a 16-bit direct binary encoded

result. It is provided, MSB first, as a 16-bit serial stream

through the SDO output pin under the control of the SCK

input pin (see Figure 3).

Ease of Use

TheLTC2450dataoutputhasnolatency,filtersettlingdelay

or redundant results associated with the conversion cycle.

Thereisaone-to-onecorrespondencebetweentheconver-

sion and the output data. Therefore, multiplexing multiple

analog input voltages requires no special actions.

The LTC2450 performs offset and full-scale calibrations

every conversion. This calibration is transparent to the

user and has no effect upon the cyclic operation described

previously. The advantage of continuous calibration is

extreme stability of the ADC performance with respect to

time and temperature.

TheLTC2450includesaproprietaryinputsamplingscheme

that reduces the average input current several orders of

magnitude as compared to traditional delta sigma archi-

tectures. This allows external filter networks to interface

directly to the LTC2450. Since the average input sampling

current is 50nA, an external RC lowpass filter using a 1k

and 0.1µF results in <1LSB error.

Reference Voltage Range

The converter uses the power supply voltage (VCC) as the

positive reference voltage (see Figure 1). Thus, the refer-

ence range is the same as the power supply range, which

extends from 2.7V to 5.5V. The LTC2450’s internal noise

level is extremely low so the output peak-to-peak noise

remains well below 1LSB for any reference voltage within

D15

LSB

SDO

SCK

D14

D13

D12

D11

D10

2450 F02

tKQ

tlSCK

thSCK

MSB

Figure 3. Data Output Timing

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