LTC2487
applicaTions inForMaTion
can be selected to form a differential input. For SGL = 1,
one of 4 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).
conversion will be performed on the internal temperature
sensorratherthantheselectedinputchannel.Thenexttwo
bits (FA and FB) are used to set the rejection frequency.
The next 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). The final three bits (GS2, GS1, GS0) are
used to set the gain. When IM = 1 (temperature measure-
ment) SPD, GS2, GS1 and GS0 will be ignored and the
device will operate in 1x mode.
Once the first word is written into the device, a second
wordmaybeinputinordertoselectaconfigurationmode.
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.
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.
The second set of configuration data can be loaded into
the device (see Table 4). The first bit (IM) is used to select
the internal temperature sensor. If IM = 1, the following
Table 4. Converter Configuration
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
EN SGL ODD A2 A1 A0 EN2 IM FA FB SPD GS2 GS1 GS0
CONVERTER CONFIGURATION
Keep Previous
0
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
X
0
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
X
X
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
X
X
X
X
X
X
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
X
X
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
X
X
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
X
X
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
Keep Previous
External Input, Gain = 1, Autocalibration
External Input, Gain = 4, Autocalibration
External Input, Gain = 8, Autocalibration
External Input, Gain = 16, Autocalibration
External Input, Gain = 32, Autocalibration
External Input, Gain = 64, Autocalibration
External Input, Gain = 128, Autocalibration
External Input, Gain = 264, Autocalibration
External Input, Gain = 1, 2x Speed
External Input, Gain = 2, 2x Speed
External Input, Gain = 4, 2x Speed
External Input, Gain = 8, 2x Speed
External Input, Gain = 16, 2x Speed
External Input, Gain = 32, 2x Speed
External Input, Gain = 64, 2x Speed
External Input, Gain = 128, 2x Speed
External Input, Simultaneous 50Hz/60Hz Rejection
External Input, 50Hz Rejection
Any
Rejection
Mode
Any
Input
Channel
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
Any
Speed
Any
Gain
External Input, 60Hz Rejection
Reserved, Do Not Use
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Temperature Input, Simultaneous 50Hz/60Hz Rejection
Temperature Input, 50Hz Rejection
Temperature Input, 60Hz Rejection
Reserved, Do Not Use
2487fa
ꢀꢆ
Linear [ Linear ]
