LTC2487 Linear Technology, LTC2487 Datasheet - Page 18

• Manufacturer Part Number: LTC2487
• Description: 16-Bit 2-/4-Channel ADC
• Manufacturer: Linear Technology

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LTC2487
applicaTions inForMaTion
Rejection Mode (FA, FB)
The LTC2487 includes a high accuracy on-chip oscillator
with no required external components. Coupled with an
integrated fourth order digital low pass filter, the LTC2487
rejects line frequency noise. In the default mode, the
LTC2487 simultaneously rejects 50Hz and 60Hz by at least
87dB. If more rejection is required, the LTC2487 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 1x and 2x mode there is no
latency. This enables input steps or multiplexer changes
to settle in a single conversion cycle, easing system over-
head and increasing the effective conversion rate. During
temperature measurements, the 1x mode is always used
independent of the value of SPD.
Table 5a. Performance vs Gain in Normal Speed Mode (V
GAIN
Input Span
LSB
Noise Free Resolution*
Gain Error
Offset Error
Table 5b. Performance vs Gain in 2x Speed Mode (V
GAIN
Input Span
LSB
Noise Free Resolution*
Gain Error
Offset Error
*The resolution in counts is calculated as the FS divided by LSB or the RMS noise value, whichever is larger.

65536
65536
±2.5
38.1
±2.5
38.1
200
0.5
1
5
1
5
±0.625
65536
65536
±1.25
9.54
19.1
200
0.5
4
5
2
5
CC
±0.312
±0.625
65536
65536
4.77
9.54
200
0.5
8
5
= 5V, V
4
5
CC
= 5V, V
REF
±0.156
±0.312
65536
65536
2.38
= 5V)
4.77
200
0.5
16
REF
5
8
5
GAIN (GS2, GS1, GS0)
The input referred gain of the LTC2487 is adjustable
from 1 to 256 (see Tables 5a and 5b). With a gain of 1,
the differential input range is ±V
mode input range is rail-to-rail. As the gain is increased,
the differential input range is reduced to ±0.5 • V
but the common mode input range remains rail-to-rail.
As the differential gain is increased, low level voltages
are digitized with greater resolution. At a gain of 256, the
LTC2487 digitizes an input signal range of ±9.76mV with
over 16,000 counts.
Temperature Sensor
The LTC2487 includes an integrated temperature sen-
sor. The temperature sensor is selected by setting
IM = 1. 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
= 5V)
±0.156
65536
65536
±78m
1.19
2.38
200
0.5
32
16
5
5
65536
65536
±39m
0.596
±78m
1.19
200
0.5
64
32
5
5
±19.5m
32768
45875
0.298
±39m
0.596
128
200
0.5
64
5
5
REF
/2 and the common
±9.76m
±19.5m
16384
22937
0.149
0.298
256
128
200
0.5
8
5
REF
ppm of FS
ppm of FS
Counts
Counts
/Gain
UNIT
UNIT
2487fa
REF
µV
µV
µV
µV
V
V