ltc2484 Linear Technology Corporation, ltc2484 Datasheet - Page 37

• Manufacturer Part Number: ltc2484
• Description: 24-bit Delta Sigma Adc With Easy Drive Input Current Cancellation
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
rejection identical as that for the 1x speed mode. The
averaging operation still keeps the output rate with the
following algorithm:
……
The main advantage of the running average is that it
achieves simultaneous 50Hz/60Hz rejection at twice the
effective output rate, as shown in Figure 42. The raw
output data provides a better than 70dB rejection over
48Hz to 62.4Hz, which covers both 50Hz ±2% and 60Hz
±2%. With running average on, the rejection is better than
87dB for both 50Hz ±2% and 60Hz ±2%.
Complete Thermocouple Measurement System with
Cold Junction Compensation
The LTC2484 is ideal for direct digitization of thermocouples
and other low voltage output sensors. The input has a typical
offset error of 500nV (2.5µV max) offset drift of 10nV/°C
and a noise level of 600nV
Figure 44 (last page of this data sheet) is a complete type
K thermocouple meter. The only signal conditioning is a
simple surge protection network. In any thermocouple
meter, the cold junction temperature sensor must be at the
Result 1 = average (sample 0, sample 1)
Result 2 = average (sample 1, sample 2)
Result n = average (sample n – 1, sample n)
U
NC1M4V0
U
G1
RMS
+
.
2
IN OUT
LT1236
GND
W
TRIM
4
6
5
R7
8k
R8
1k
(OMEGA MPJ-K-F)
THERMOCOUPLE
U
Figure 43. Calibration Setup
TYPE K
JACK
ISOTHERMAL
R2
2k
26.3C
same temperature as the junction between the thermo-
couple materials and the copper printed circuit board
traces. The tiny LTC2484 can be tucked neatly underneath
an Omega MPJ-K-F thermocouple socket ensuring close
thermal coupling.
The LTC2484’s 1.4mV/°C PTAT circuit measures the cold
junction temperature. Once the thermocouple voltage and
cold junction temperature are known, there are many
ways of calculating the thermocouple temperature includ-
ing a straight-line approximation, lookup tables or a
polynomial curve fit. Calibration is performed by applying
an accurate 500mV to the ADC input derived from an
LT
with an accurate thermometer as shown in Figure 43. In
calibration mode, the up and down buttons are used to
adjust the local temperature reading until it matches an
accurate thermometer. Both the voltage and temperature
calibration are easily automated.
The complete microcontroller code for this application is
available on the LTC2484 product webpage at:
http://www.linear.com
It can be used as a template for may different instruments
and it illustrates how to generate calibration coefficients
for the onboard temperature sensor. Extensive comments
detail the operation of the program. The read_LTC2484()
function controls the operation of the LTC2484 and is
listed below for reference.
®
1236 reference and measuring the local temperature
4
5
IN
IN
+
–
GND
REF
LTC2484
3
8
GND
V
5V
CC
2
11
SDO
SCK
SDI
CS
F
O
C8
1µF
6
9
7
1
10
2484 F43
C7
0.1µF
LTC2484
37
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