LTC2420IS8#TRPBF Linear Technology, LTC2420IS8#TRPBF Datasheet - Page 33

• Manufacturer Part Number: LTC2420IS8#TRPBF
• Description: IC ADC 20BIT MICRPWR W/OSC 8SOIC
• Manufacturer: Linear Technology

Specifications of LTC2420IS8#TRPBF

• 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: Lead free / RoHS Compliant

Using a Low Power Precision Reference
The circuit in Figure 38 shows the connections and by-
passing for an LT1461-2.5 as a 2.5V reference. The
LT1461 is a bandgap reference capable of 3ppm/ C tem-
perature stability yet consumes only 45 A of current. The
1k resistor between the reference and the ADC reduces the
transient load changes associated with sampling and
produces optimal results. This reference will not impact
the noise level of the LTC2420 if signals are less than 60%
full scale, and only marginally increases noise approach-
ing full scale. Even lower power references can be used if
only the lower end of the LTC2420 input range is required.
A Differential to Single-Ended Analog Front End
Figure 39 shows the LT1167 as a means of sensing
differential signals. The noise performance of the LT1167
is such that for gains less than 200, the noise floor of the
LTC2420 remains the dominant noise source. At the point
TYPICAL APPLICATIO S
5V
Figure 39. A Differential to Single-Ended Analog Front End
U
RECOMMENDED R
A
V
5V
=
49.4k
3.5k
R
4
R
G
G
Figure 38. Low Power Reference
2
1
8
3
+ 1
0.1 F
CER
+
–
LT1167
G
–5V
: 500 , 0.1%
5ppm/ C
IN
LT1461-2.5
5V
GND
5
OUT
6
+
22
where the noise of the amplifier begins to dominate, the
input referred noise is essentially that of the instrumenta-
tion amplifier. The linearity of the instrumentation ampli-
fier does, however, degrade at higher gains. As a result, if
the full linearity of the LTC2420 is desired, gain in the
instrumentation amplifier should be limited to less than
100, possibly requiring averaging multiple samples to
extend the resolution below the noise floor. The noise level
of the LT1167 at gains greater than 100 is on the order of
50nV
degrade this below 0.1Hz. The introduction of a filter
between the amplifier and the LTC2420 may improve
noise levels under some circumstances by reducing noise
bandwidth. Note that temperature offset drift effects enve-
lope detection in the input of the LT1167 if exposed to RFI,
thermocouple voltages in connectors, resistors and sol-
dered junctions can all compromise results, appearing as
drift or noise. Turbulent airflow over this circuitry should
be avoided.
OPTIONAL
10 F
16V
TANT
RMS
10 F
1 F
1k
2428 F39
, although, 1/f noise and temperature effects may
+
5k
TO
LTC2420
REF
2420 F38
1
2
3
4
LTC2420
LTC2420
33