ltc2493 Linear Technology Corporation, ltc2493 Datasheet - Page 19

• Manufacturer Part Number: ltc2493
• Description: 24-bit 2-/4-channel Delta Sigma Adc With Easy Drive Input Current Cancellation And I2c Interface
• Manufacturer: Linear Technology Corporation

applicaTions inForMaTion
Speed Mode (SPD)
Every conversion cycle, two conversions are combined
to remove the offset (default mode). This result is free
from offset and drift. In applications where the offset is
not critical, the auto-calibration feature can be disabled
with the benefit of twice the output rate.
While operating in the 2x mode (SPD = 1), the linearity
and full-scale errors are unchanged from the 1x mode
performance. In both the 1x and 2x mode there is no
latency. This enables input steps or multiplexer changes
to settle in a single conversion cycle, easing system over-
head and increasing the effective conversion rate. During
temperature measurements, the 1x mode is always used
independent of the value of SPD.
Temperature Sensor
The LTC2493 includes an integrated temperature sen-
sor. The temperature sensor is selected by setting
IM = 1. 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 27ºC
(300ºK), with a slope of 93.5µV/ºC independent of V
Figure 4. Internal PTAT Digital Output vs Temperature
140000
120000
100000
80000
60000
40000
20000
0
0
V
V
SLOPE = 314 LSB
CC
REF
= 5V
= 5V
100
TEMPERATURE (K)
24
/K
200
300
2493 F04
400
REF
(see Figures 4 and 5). Slope calibration is not required if
the reference voltage (V
a slope of 314 LSBs
from the output code (where DATAOUT
representation of the 24-bit result) for a 5V reference using
the following formula:
If a different value of V
output is:
If the value of V
by measuring the temperature sensor at a known tempera-
ture T
This value of slope can be used to calculate further tem-
perature readings using:
All Kelvin temperature readings can be converted to T
(ºC) using the fundamental equation:
T
T
T
SLOPE
T
K
C
K
K
= T
N
=
=
=
(in K) and using the following formula:
DATAOUT
DATAOUT
K
DATAOUT
– 273
=
SLOPE
Figure 5. Absolute Temperature Error
–1
–2
–3
–4
–5
314
5
4
3
2
1
0
DATAOUT
–55
REF
1570
–30
T
is not known, the slope is determined
24
24
24
N
24
/ºC. The temperature is calculated
–5
in Kelvin
•
REF
TEMPERATURE (°C)
V
24
REF
REF
) is known. A 5V reference has
20
is used, the temperature
45
in Kelvin
70
95
LTC2493
24
2493 F05
is the decimal
120

2493fa
C