Datasheet

LTC2498
21
2498ff
applications inForMation
Figure 4. Internal PTAT Digital Output vs Temperature
Slope calibration is not required if the reference volt-
age (V
REF
) is known. A 5V reference has a slope of 314
LSBs
24
/°C. The temperature is calculated from the output
code (DATAOUT
24
) 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 temperature
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
SERIAL INTERFACE TIMING MODES
The LTC2498’s 4-wire interface is SPI and MICROWIRE
compatible. This interface offers several flexible 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
O
= LOW or f
O
= HIGH) or an external oscillator
connected to the f
O
pin. For each mode, the operating cycle,
data input format, data output format, and performance
remain the same. Refer to Table 5 for a summary.
Figure 5. Absolute Temperature Error
Table 5. LTC2498 Interface Timing Modes
CONFIGURATION
SCK
SOURCE
CONVERSION
CYCLE CONTROL
DATA OUTPUT
CONTROL
CONNECTION AND
WAVEFORMS
External SCK, Single Cycle
Conversion
External CS and SCK CS and SCK Figures 6, 7
External SCK, 3-Wire I/O External SCK SCK Figure 8
Internal SCK, Single Cycle
Conversion
Internal
CS↓ CS↓
Figures 9, 10
Internal SCK, 3-Wire I/O,
Continuous Conversion
Internal Continuous Internal Figure 11
TEMPERATURE (°K)
0
DATAOUT
24
60000
80000
100000
120000
140000
400
2498 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
2498 F05
–5