LTC2494 Linear Technology, LTC2494 Datasheet - Page 20

• Manufacturer Part Number: LTC2494
• Description: 16-Bit 8-/16-Channel ADC
• Manufacturer: Linear Technology

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APPLICATIONS INFORMATION
LTC2494
Table 5a. Performance vs Gain in Normal Speed Mode (V
GAIN
Input Span
LSB
Noise Free Resolution*
Gain Error
Offset Error
Table 5b. Performance vs Gain in 2x Speed Mode (V
GAIN
Input Span
LSB
Noise Free Resolution*
Gain Error
Offset Error
*The resolution in counts is calculated as the FS divided by LSB or the RMS noise value, whichever is larger.
Temperature Sensor
The LTC2494 includes an integrated temperature sensor.
The temperature sensor is selected by setting IM = 1.
During temperature readings, MUXOUTN/MUXOUTP
remains connected to the selected input channel. The
ADC internally connects to the temperature sensor and
performs a conversion.
The digital output is proportional to the absolute tem-
perature of the device. This feature allows the converter
to perform cold junction compensation for external
thermocouples or continuously remove the temperature
effects of external sensors.
The internal temperature sensor output is 28mV at 27°C
(300°K), with a slope of 93.5μV/°C independent of V
Slope calibration is not required if the reference voltage
(V
LSBs
code (where DATAOUT
the 16-bit result) for a 5V reference using the following
formula:
If a different value of V
is:
20
REF
T
T
K
K
16
) is known. A 5V reference has a slope of 2.45
= DATAOUT
= DATAOUT
/°C. The temperature is calculated from the output
16
16
/2.45 in Kelvin
• V
REF
16
REF
65536
65536
±2.5
38.1
±2.5
38.1
is the decimal representation of
200
is used, the temperature output
0.5
/12.25 in Kelvin
1
5
1
5
±0.625
65536
65536
±1.25
9.54
19.1
200
0.5
4
5
2
5
CC
±0.312
±0.625
65536
65536
4.77
9.54
200
0.5
8
5
= 5V, V
4
5
CC
= 5V, V
REF
REF
.
±0.156
±0.312
65536
65536
= 5V)
2.38
4.77
200
0.5
16
REF
5
8
5
If the value of V
measuring the temperature sensor at a known temperature
T
This value of slope can be used to calculate further tem-
perature readings using:
All Kelvin temperature readings can be converted to T
(°C) using the fundamental equation:
SERIAL INTERFACE TIMING MODES
The LTC2494’s 4-wire interface is SPI and MICROWIRE
compatible. This interface offers several fl exible modes
of operation. These include internal/external serial clock,
3- or 4-wire I/O, single cycle or continuous conversion. The
following sections describe each of these timing modes
in detail. In all cases, the converter can use the internal
oscillator (F
to the F
input format, data output format, and performance remain
the same. Refer to Table 6 for a summary.
= 5V)
N
SLOPE = DATAOUT
T
T
(in °K) and using the following formula:
K
C
= DATAOUT
= T
±0.156
65536
65536
±78m
1.19
2.38
200
0.5
32
16
O
5
5
K
pin. For each mode, the operating cycle, data
– 273
O
= LOW) or an external oscillator connected
REF
65536
65536
±39m
0.596
±78m
16
1.19
200
is not known, the slope is determined by
0.5
64
32
5
5
/SLOPE
16
/T
N
±19.5m
32768
45875
0.298
±39m
0.596
128
200
0.5
64
5
5
±9.76m
±19.5m
16384
22937
0.149
0.298
256
128
200
0.5
8
5
ppm of FS
ppm of FS
Counts
Counts
UNIT
UNIT
2494fb
μV
μV
μV
μV
V
V
C