LTC2483 datasheet(8/20 Pages) LINER

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LTC2450-1

24501fb

APPLICATIONS INFORMATION

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 input is at ground (a zero scale input) and an “all

one” digital result when the input is at VCC (a full-scale

input). 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 LTC2450-1 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).

During the data output operation the CS input pin must

be pulled low (CS = LOW). The data output process starts

with the most signiﬁcant bit of the result being present

at the SDO output pin (SDO = D15) once CS goes low.

A new data bit appears at the SDO output pin following

every falling edge detected at the SCK input pin. The

output data can be reliably latched by the user using the

rising edge of SCK.

Ease of Use

The LTC2450-1 data output has no latency, ﬁlter settling

delay or redundant results associated with the conversion

cycle. There is a one-to-one correspondence between the

conversion and the output data. Therefore, multiplexing

multiple analog input voltages requires no special ac-

tions.

The LTC2450-1 includes a proprietary input sampling

scheme that reduces the average input current several

orders of magnitude as compared to traditional delta

sigma architectures. This allows external ﬁlter networks

to interface directly to the LTC2450-1. Since the average

input sampling current is 50nA, an external RC lowpass

ﬁlter using a 1kΩ 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 LTC2450-1’s internal noise

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

remains well below 1LSB for any reference voltage within

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).

Figure 3. Data Output Timing

D15

LSB

SDO

SCK

D14

D13

D12

D11

D10

24501 F03

tKQ

tlSCK

thSCK

MSB

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