Datasheet

LTC2499
21
2499fd
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
Initiating a New Conversion
When the LTC2499 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 LTC2499 starts a new conversion once a STOP
condition is issued by the master or all 32 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).
LTC2499 Address
The LTC2499 has three address pins (CA0, CA1, CA2).
Each may be tied HIGH, LOW, or left floating enabling one
of 27 possible addresses (see Table 5).
In addition to the configurable addresses listed in Table 5,
the LTC2499 also contains a global address (1110111)
which may be used for synchronizing multiple LTC2499s or
other LTC24XX delta-sigma I
2
C devices (see Synchronizing
Multiple LTC2499s with a Global Address Call section).
Operation Sequence
The LTC2499 acts as a transmitter or receiver, as shown
in Figure 6. The device may be programmed to perform
several functions. These include input channel selection,
measure the internal temperature, selecting the line fre-
quency rejection (50Hz, 60Hz, or simultaneous 50Hz and
60Hz), and a 2x speed mode.
Table 5. Address Assignment
CA2 CA1 CA0 ADDRESS
LOW LOW LOW 0010100
LOW LOW HIGH 0010110
LOW LOW Float 0010101
LOW HIGH LOW 0100110
LOW HIGH HIGH 0110100
LOW HIGH Float 0100111
LOW Float LOW 0010111
LOW Float HIGH 0100101
LOW Float Float 0100100
HIGH LOW LOW 1010110
HIGH LOW HIGH 1100100
HIGH LOW Float 1010111
HIGH HIGH LOW 1110100
HIGH HIGH HIGH 1110110
HIGH HIGH Float 1110101
HIGH Float LOW 1100101
HIGH Float HIGH 1100111
HIGH Float Float 1100110
Float LOW LOW 0110101
Float LOW HIGH 0110111
Float LOW Float 0110110
Float HIGH LOW 1000111
Float HIGH HIGH 1010101
Float HIGH Float 1010100
Float Float LOW 1000100
Float Float HIGH 1000110
Float Float Float 1000101
Continuous Read
In applications where the input channel/configuration does
not need to change for each cycle, the conversion can be
continuously performed and read without a write cycle
(see Figure 7). The configuration/input channel remains
unchanged from the last value written into the device. If
the device has not been written to since power-up, the
configuration is set to the default value. At the end of a
read operation, a new conversion automatically begins.
At the conclusion of the conversion cycle, the next result
may be read using the method described above. If the
conversion cycle is not concluded and a valid address
applications inForMation