Datasheet

LTC2499
19
2499fd
nels can be selected to form a differential input. For SGL
= 1, one of 16 channels is selected as the positive input.
The negative input is COM for all single-ended operations.
The remaining four bits (ODD, A2, A1, A0) determine
which channel(s) is/are selected and the polarity (for a
differential input).
Once the first word is written into the device, a second
word may be input in order to select a configuration mode.
The first bit of the second word is the enable bit for the
conversion configuration (EN2). If this bit is set to 0, then
the next conversion is performed using the previously
selected converter configuration.
A new configuration can be loaded into the device by
setting EN2 = 1 (see Table 4). The first bit (IM) is used
to select the internal temperature sensor. If IM = 1, the
following conversion will be performed on the internal
temperature sensor rather than the selected input channel.
The next two bits (FA and FB) are used to set the rejection
frequency. The final bit (SPD) is used to select either the
1x output rate if SPD = 0 (auto-calibration is enabled and
the offset is continuously calibrated and removed from
the final conversion result) or the 2x output rate if SPD
= 1 (offset calibration disabled, multiplexing output rates
up to 15Hz with no latency). When IM = 1 (temperature
measurement) SPD will be ignored and the device will
operate in 1x mode.
The configuration remains valid until a new input word
with EN = 1 (the first three bits are 101 for the first word)
and EN2 = 1 (for the second write byte) is shifted into
the device.
Table 4. Converter Configuration
1 0 EN SGL ODD A2 A1 A0 EN2 IM FA FB SPD CONVERTER CONFIGURATION
1 0 0 X X X X X X X X X X Keep Previous
1 0 1 X X X X X 0 X X X X Keep Previous
0 0 1 X X X X X X X X X X Keep Previous
1 0 1 X X X X X 1 0 0 0 0 External Input (See Table 3)
50Hz/60Hz Rejection, 1x
1 0 1 X X X X X 1 0 0 1 0 External Input (See Table 3)
50Hz Rejection, 1x
1 0 1 X X X X X 1 0 1 0 0 External Input (See Table 3)
60Hz Rejection, 1x
1 0 1 X X X X X 1 0 0 0 1 External Input (See Table 3)
50Hz/60Hz Rejection, 2x
1 0 1 X X X X X 1 0 0 1 1 External Input (See Table 3)
50Hz Rejection, 2x
1 0 1 X X X X X 1 0 1 0 1 External Input (See Table 3)
60Hz Rejection, 2x
1 0 1 X X X X X 1 1 0 0 X Measure Temperature
50Hz/60Hz Rejection, 1x
1 0 1 X X X X X 1 1 0 1 X Measure Temperature
50Hz Rejection, 1x
1 0 1 X X X X X 1 1 1 0 X Measure Temperature
60Hz Rejection, 1x
1 0 1 X X X X X 1 X 1 1 X Reserved, Do Not Use
applications inForMation