LTC2413 LINER [Linear Technology], LTC2413 Datasheet - Page 39

• Manufacturer Part Number: LTC2413
• Description: 24-Bit No Latency ADC, with Simultaneous 50Hz/60Hz Rejection
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
be a source of error. The fact that input offset voltage has
relatively little effect on overall error may lead one to use
low performance amplifiers for this application. Note that
the gain of a device such as an LF156, (25V/mV over
temperature) will produce a worst-case error of –180ppm
at a noise gain of 3, such as would be encountered in an
inverting gain of 2, to produce –10V from a 5V reference.
The error associated with the 10V excitation would be
–80ppm. Hence, overall reference error could be as high
as 130ppm, the average of the two.
Figure 50 shows a similar scheme to provide excitation
using resistor arrays to produce precise gain. The circuit
is configured to provide 10V and –5V excitation to the
bridge, producing a common mode voltage at the input to
the LTC2413 of 2.5V, maximizing the AC input range for
applications where induced 60Hz could reach amplitudes
up to 2V
RMS
.
U
BRIDGE
350
+
U
1 F
A
V
= 9.95 =
Figure 45. Bridge Amplification Using a Single Amplifier
W
4.99k
R1
R1 + 175
R1 + R2
3
2
U
+
LTC1050S8
–
5V
7
4
46.4k
R2
0.1 V
6
The circuits in Figures 48 and 50 could be used where
multiple bridge circuits are involved and bridge output can
be multiplexed onto a single LTC2413, via an inexpensive
multiplexer such as the 74HC4052.
Figure 49 shows the use of an LTC2413 with a differential
multiplexer. This is an inexpensive multiplexer that will
contribute some error due to leakage if used directly with
the output from the bridge, or if resistors are inserted as
a protection mechanism from overvoltage. Although the
bridge output may be within the input range of the A/D and
multiplexer in normal operation, some thought should be
given to fault conditions that could result in full excitation
voltage at the inputs to the multiplexer or ADC. The use of
amplification prior to the multiplexer will largely eliminate
errors associated with channel leakage developing error
voltages in the source impedance.
175
1 F
+
20k
20k
10 F
3
4
5
6
+
REF
REF
IN
IN
+
–
LTC2413
+
–
GND
V
CC
1, 7, 8, 9,
10, 15, 16
2
0.1 F
2413 F45
5V
LTC2413
sn2413 2413fs
39