LTC2420IS8#TR Linear Technology, LTC2420IS8#TR Datasheet - Page 31

• Manufacturer Part Number: LTC2420IS8#TR
• Description: IC ADC 20BIT MICROPOWER 8SOIC
• Manufacturer: Linear Technology

Specifications of LTC2420IS8#TR

• Number Of Bits: 20
• Sampling Rate (per Second): 7.5
• Data Interface: MICROWIRE™, Serial, SPI™
• Number Of Converters: 2
• Power Dissipation (max): 1mW
• Voltage Supply Source: Single Supply
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (0.154", 3.90mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Single-Chip Instrumentation Amplifier
for the LTC2420
The circuit in Figure 37 is a simple solution for processing
differential signals in pressure transducer, weigh scale or
strain gauge applications that can operate on a supply
voltage range of 5V to 15V. The circuit uses an LT
single-chip instrumentation amplifier to perform a differ-
ential to single-ended conversion. The amplifier’s output
voltage is applied to the LTC2420’s input and converted to
a digital value with an overall accuracy exceeding 17 bits
(0.0008%). Key circuit performance results are shown in
Table 5.
The practical gain range for this topology as shown is from
5 to 100 because the LTC2420’s wide dynamic range
makes gains below 5 virtually unnecessary, whereas gains
up to 100 significantly reduce the input referred noise.
The optional passive RC lowpass filter between the
amplifier’s output and the LTC2420’s input attenuates
high frequency noise and its effects. Typically, the filter
TYPICAL APPLICATIO S
DIFFERENTIAL
INPUT
Figure 37. The LT1920 is a Simple Solution That Converts a Differential Input
to a Ground Referred Single-Ended Signal for the LTC2420
R
G
**
2
1
8
3
U
V
R
R
V
IN
IN
G
G
**R
*OPTIONAL—SEE TEXT
†
+
–
LT1920
USE SHORT LEAD LENGTHS
G
= 49.4k/(A
7
4
V
V
S
S
+
–
0.1 F
0.1 F
V
6
– 1): USE 5.49k FOR A
®
†
1920
47
R1*
†
SINGLE POINT
“STAR” GROUND
10k
C1*
1 F
R2*
reduces the magnitude of averaged noise by 30% and
improves resolution by 0.5 bit without compromising
linearity. Resistor R2 performs two functions: it isolates
C1 from the LTC2420’s input and limits the LTC2420’s
input current should its input voltage drop below –300mV
or swing above V
The LT1920 is the choice for applications where low cost
is important. For applications where more precision is
required, the LT1167 is a pin-to-pin alternative choice with
a lower offset voltage, lower input bias current and higher
gain accuracy than the LT1920. The LT1920’s maximum
total input-referred offset (V
100. At the same gain, the LT1167’s V
of 10 or 100, the LT1920’s maximum gain error is 0.3%
and its maximum gain nonlinearity is 30ppm. At the same
gains, the LT1167’s maximum gain error is 0.1% and its
maximum gain nonlinearity is 15ppm. Table 6 summa-
rizes the performance of Figure 37’s circuit using the
LT1167.
†
V
= 10; 499 FOR A
3
V
2
REFIN
V
IN
V
REF
1
GND
V
5V
CC
4
LTC2420
0.1 F
V
F
O
= 100
8
CC
SDO
SCK
CS
+ 300mV.
5
6
7
2420 F37
CHIP SELECT
SERIAL DATA OUT
SERIAL CLOCK
OST
) is 135 V for a gain of
OST
is 63 V. At gains
LTC2420
31