Datasheet

LTC2493
19
2493fd
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 2× mode (SPD = 1), the linearity
and full-scale errors are unchanged from the 2× mode
performance. In both the 2× and 2× 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 1× 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 27°C
(300°K), with a slope of 93.5µV/°C independent of V
REF
(see Figures 4 and 5). Slope calibration is not required if
the reference voltage (V
REF
) is known. A 5V reference has
a slope of 314 LSBs
24
/°C. The temperature is calculated
from the output code (where DATAOUT
24
is the decimal
representation of the 24-bit result) for a 5V reference using
the following formula:
T
K
=
DATAOUT
24
314
in Kelvin
If a different value of V
REF
is used, the temperature
output is:
T
K
=
DATAOUT
24
• V
REF
1570
in Kelvin
If the value of V
REF
is not known, the slope is determined
by measuring the temperature sensor at a known tempera-
ture T
N
(in K) and using the following formula:
SLOPE =
DATAOUT
24
T
N
This value of slope can be used to calculate further tem-
perature readings using:
T
K
=
DATAOUT
24
SLOPE
All Kelvin temperature readings can be converted to T
C
(°C) using the fundamental equation:
T
C
= T
K
– 273
TEMPERATURE (K)
0
DATAOUT
24
60000
80000
100000
120000
140000
400
2493 F04
40000
0
300200100
20000
V
CC
= 5V
V
REF
= 5V
SLOPE = 314 LSB
24
/K
TEMPERATURE (°C)
–55 –30 –5
ABSOLUTE ERROR (°C)
5
4
3
2
1
–4
–3
–2
–1
0
12095704520
2493 F05
–5
Figure 4. Internal PTAT Digital Output vs Temperature Figure 5. Absolute Temperature Error
applicaTions inForMaTion