Datasheet

LTC2487
19
2487fd
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
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
(ºC) using the fundamental equation:
T
C
= T
K
– 273
Initiating a New Conversion
When the LTC2487 fi nishes 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 LTC2487 starts a new conversion once a Stop condi-
tion 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/NAK cycle).
LTC2487 Address
The LTC2487 has two address pins (CA0, CA1). Each may
be tied high, low, or left fl oating enabling one of 9 possible
addresses (see Table 6).
In addition to the confi gurable addresses listed in Table 6,
the LTC2487 also contains a global address (1110111)
which may be used for synchronizing multiple LTC2487s or
other LTC24XX delta-sigma I
2
C devices (see Synchronizing
Multiple LTC2487s with a Global Address Call section).
APPLICATIONS INFORMATION
Figure 4. Internal PTAT Digital Output vs Temperature
Figure 5. Absolute Temperature Error
TEMPERATURE (°C)
–55 –30 –5
ABSOLUTE ERROR (°C)
5
4
3
2
1
–4
–3
–2
–1
0
12095704520
2487 F05
–5
TEMPERATURE (K)
0
DATAOUT
16
480
640
800
960
1020
400
2487 F04
320
0
300200100
160
V
CC
= 5V
V
REF
= 5V
SLOPE = 2.45 LSB
16
/K
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
inKelvin
K
=
16
245.
If a different value of V
REF
is used, the temperature
output is:
T
DATAOUT
• V /12.25
inKelvin
K
REF
=
16