LTC2412 Linear Technology, LTC2412 Datasheet - Page 33

• Manufacturer Part Number: LTC2412
• Description: 2-Channel Differential Input 24-Bit No Latency DS ADC
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
of full scale. In many industrial applications, it is not un-
common to have to measure microvolt level signals super-
imposed over volt level perturbations and LTC2412 is
eminently suited for such tasks. When the perturbation is
differential, the specification of interest is the normal mode
rejection for large input signal levels. With a reference
voltage V
tial input range of 5V peak-to-peak. Figures 39 and 40 show
measurement results for the LTC2412 normal mode rejec-
tion ratio with a 7.5V peak-to-peak (150% of full scale)
input signal superimposed over the more traditional nor-
mal mode rejection ratio results obtained with a 5V peak-
to-peak (full scale) input signal. In Figure 39, the LTC2412
uses the internal oscillator with the notch set at 60Hz (F
= LOW) and in Figure 40 it uses the internal oscillator with
the notch set at 50Hz (F
rejection performance is maintained with no compromises
in this extreme situation. When operating with large input
signal levels, the user must observe that such signals do
not violate the device absolute maximum ratings.
Figure 38. Input Normal Mode Rejection vs Input Frequency with Input Perturbation of 100% Full Scale (50Hz Notch)
REF
= 5V, the LTC2412 has a full-scale differen-
U
O
= HIGH). It is clear that the LTC2412
–100
–120
–20
–40
– 60
–80
U
0
0
12.5 25 37.5 50 62.5 75 87.5 100 112.5 125 137.5 150 162.5 175 187.5 200
W
U
INPUT FREQUENCY (Hz)
O
Measuring Barometric Pressure and Temperature
with a Single Sensor
Figure 41 shows the LTC2412 measuring both tempera-
ture and pressure from an Intersema model MS5401-BM
absolute pressure sensor. The bridge has a nominal
impedance of 3.4k, a temperature coefficient of resistance
of 2900ppm/ C and a temperature coefficient of span of
–1900ppm/ C. R1 provides first order temperature com-
pensation of the output span by causing the bridge voltage
to increase by 1900ppm/ C, offsetting the –1900ppm/ C
TC of span. R1 should have a much smaller TC than that
of the bridge resistance; 50ppm/ C or less is satisfactory.
In addition to compensating the bridge output span, this
circuit also provides a convenient way to measure ambient
temperature. Channel 1 of the LTC2412 measures the
bridge excitation voltage, which has a slope of approxi-
mately 3.2mV/ C. Channel 0 measures the bridge output,
which has a slope of 50mV/bar. The temperature reading
can also be used for second order compensation of the
pressure reading.
MEASURED DATA
CALCULATED DATA
V
REF
REF
V
V
F
T
O
CC
INCM
IN(P-P)
A
= 5V
= 25 C
+
–
= 5V
= 5V
= GND
= 2.5V
= 5V
2412 F38
LTC2412
33
2412f