Datasheet

LTC2485
17
2485fc
APPLICATIONS INFORMATION
OPERATION SEQUENCE
The LTC2485 acts as a transmitter or receiver. The device
may be programmed to perform several functions. These
include measuring an external differential input signal or
an integrated temperature sensor, selecting line frequency
rejection (50Hz, 60Hz, or simultaneous 50Hz and 60Hz),
and a 2x speed up mode.
Continuous Read
In applications where the confi guration does not need
to change for each conversion cycle, the conversion
result can be continuously read. The confi guration
remains unchanged from the last value written into
the device. If the device has not been written to since
power up, the confi guration is set to the default value
(Input External, simultaneous 50Hz/60Hz rejection, and
1x speed mode). The operation sequence is shown in
Figure 6. When the conversion is fi nished, the device
may be addressed for a read operation. At the end of a
read operation, a new conversion begins. At the conclu-
sion 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 selects the
device, the LTC2485 generates a NAK signal indicating
the conversion cycle is in progress.
Continuous Read/Write
Once the conversion cycle is concluded, the LTC2485 can
be written to then read from, using the repeated Start
(Sr) command.
Figure 7 shows a cycle which begins with a data Write, a
repeated start, followed by a read, and concluded with a
stop command. The following conversion begins after all 32
bits are read out of the device or after the STOP command
and uses the newly programmed confi guration data.
S ACK DATA Sr DATA TRANSFERRING P
SLEEP DATA INPUT/OUTPUT CONVERSIONCONVERSION
7-BIT ADDRESS
R/W
2485 F05
7-BIT ADDRESS
CONVERSION CONVERSION
CONVERSION
SLEEP SLEEPDATA OUTPUT DATA OUTPUT
7-BIT ADDRESSSSRRACK ACKREAD READPP
2485 F06
7-BIT ADDRESS
CONVERSION CONVERSIONADDRESSSLEEP DATA OUTPUTDATA INPUT
7-BIT ADDRESSS RW ACK ACKWRITE Sr PREAD
2485 F07
Figure 5. The LTC2485 Conversion Sequence
Figure 6. Consecutive Reading at the Same Confi guration
Figure 7. Write, Read, Start Conversion