Datasheet

LTC2498
20
2498ff
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 3 bits are 101) and
EN2 = 1 is shifted into the device.
Rejection Mode (FA, FB)
The LTC2498 includes a high accuracy on-chip oscillator
with no required external components. Coupled with an
integrated 4th order digital lowpass filter, the LTC2498
rejects line frequency noise. In the default mode, the
LTC2498 simultaneously rejects 50Hz and 60Hz by at least
87dB. If more rejection is required, the LTC2498 can be
configured to reject 50Hz or 60Hz to better than 110dB.
Speed Mode (SPD)
Every conversion cycle, two conversions are combined to
remove the offset (default mode). This result is free from
offset and drift. In applications where the offset is not
critical, the auto-calibration feature can be disabled with
the benefit of twice the output rate. While operating in the
2x mode (SPD = 1), the linearity and full-scale errors are
unchanged from the 1x mode performance. In
both the 1
x
and 2x mode there is no latency. This enables input steps
or multiplexer changes to settle in a single conversion
cycle easing system overhead and increasing the effective
conversion rate. During temperature measurements, the
1x mode is always used independent of the value of SPD.
Temperature Sensor
The LTC2498 includes an integrated temperature sensor.
The temperature sensor is selected by setting IM = 1.
During temperature readings, MUXOUTN/MUXOUTP
remains connected to the selected input channel. The
ADC internally connects to the temperature sensor and
performs a conversion.
The digital output is proportional to the absolute tem-
perature of the device. This feature allows the converter
to perform cold junction compensation for external
thermocouples or continuously remove the temperature
effects of external sensors.
The internal temperature sensor output is 28mV at 27°C
(300°K), with a slope of 93.5µV/°C independent of V
REF
.
applications inForMation
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 (Change Channel)
0 0 0 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 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