Datasheet

LTC2495
21
2495fd
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 2.45 LSBs
16
/°C. The temperature is calculated
from the output code (where DATAOUT
16
is the decimal
representation of the 16-bit result) for a 5V reference using
the following formula:
T
DATAOUT
in Kelvin
K
=
16
2 45.
If a different value of V
REF
is used, the temperature
output is:
T
DATAOUT V
in Kelvin
K
REF
=
16
12 25
•
.
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
T
N
=
16
This value of slope can be used to calculate further tem-
perature readings using:
T
DATAOUT
SLOPE
K
=
16
All Kelvin temperature readings can be converted to T
C
(°C) using the fundamental equation:
T
C
= T
K
– 273
Initiating a New Conversion
When the LTC2495 finishes a conversion, it automatically
enters the sleep state. Once in the sleep state, the device is
ready for a read operation. After the device acknowledges
a read request, the device exits the sleep state and enters
the data output state. The data output state concludes
and the LTC2495 starts a new conversion once a STOP
condition is issued by the master or all 24 bits of data are
read out of the device.
During the data read cycle, a STOP command may be issued
by the master controller in order to start a new conversion
and abort the data transfer. This STOP command must be
issued during the ninth clock cycle of a byte read when
the bus is free (the ACK/NACK cycle).
LTC2495 Address
The LTC2495 has three address pins (CA0, CA1, CA2).
Each may be tied HIGH, LOW, or left floating enabling one
of 27 possible addresses (see Table 6).
In addition to the configurable addresses listed in Table 6,
the LTC2495 also contains a global address (1110111)
which may be used for synchronizing multiple LTC2495s or
other LTC24XX delta-sigma I
2
C devices (see Synchronizing
Multiple LTC2495s with a Global Address Call section).
applications inForMation
Figure 4. Internal PTAT Digital Output vs Temperature
Figure 5. Absolute Temperature Error
TEMPERATURE (K)
0
DATAOUT
16
450
600
750
900
1050
400
2495 F04
300
0
300200100
150
V
CC
= 5V
V
REF
= 5V
SLOPE = 2.45 LSB
16
/K
TEMPERATURE (°C)
–55 –30 –5
ABSOLUTE ERROR (°C)
5
4
3
2
1
–4
–3
–2
–1
0
12095704520
2495 F05
–5