LTC2428CG Linear Technology, LTC2428CG Datasheet - Page 29

• Manufacturer Part Number: LTC2428CG
• Description: IC ADC 20BIT 8CH MICROPWR 28SSOP
• Manufacturer: Linear Technology

Specifications of LTC2428CG

• Number Of Bits: 20
• Sampling Rate (per Second): 7.5
• Data Interface: MICROWIRE™, Serial, SPI™
• Number Of Converters: 1
• Power Dissipation (max): 1mW
• Voltage Supply Source: Single Supply
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 28-SSOP (0.200", 5.30mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

APPLICATIONS
than 60% full scale, and only marginally increases noise
approaching full scale. Even lower power references can
be used if only the lower end of the LTC2424/LTC2428
input range is required.
2.051MHz Oscillator for 100sps Output Ratio
The oscillator circuit shown in Figure 31 can be used to
drive the F
LTC2420 for applications that do not require a notch at 50
or 60Hz. This oscillator is not sensitive to hysteresis
voltage of a Schmitt trigger device as are simpler
relaxation oscillators using the 74HC14 or similar de-
vices. The circuit can be tuned over a 3-1 range with only
one resistor and can be gated. The use of transmission
gates could be used to shift the frequency in order to
provide setable conversion rates.
Pseudodifferential Multichannel Bridge Digitizer and
Digital Cold Junction Compensation
The circuit shown in Figure 32 enables pseudodifferential
measurements of several bridge transducers and abso-
lute temperature measurement.
THERMISTOR
5V
0.1 F
CER
O
pin, boosting the conversion rate of the
Figure 30. Low Power Reference
Figure 32. Pseudodifferential Multichannel Bridge Digitizer and Digital Cold Junction Compensation
THERMOCOUPLE
IN
LT1461-2.5
GND
U
OUT
INFORMATION
+
U
10 F
16V
TANT
W
1k
TO
LTC2424/LTC2428
FS
SET
24248 F30
U
Consecutive readings are performed on each side of the
bridge by selecting the appropriate channel on the
LTC2428. Each output is digitized and the results digitally
subtracted to obtain the pseudodifferential result. Several
bridge transducers may be digitized in this manner.
In order to measure absolute temperature with a thermo-
couple, cold junction compensation must be performed.
Channel 6 measures the output of the thermocouple while
channel 7 measures the output of the cold junction sensor
(diode, thermistor, etc.). This enables digital cold junction
compensation of the thermocouple output. The tempera-
ture measurement may then be used to compensate the
temperature effects of the bridge transducers.
10
11
12
13
14
15
17
100smps, F
30smps, F
U1: 74HC14 OR EQUIVALENT
9
5 ZS
CH0
CH1
CH2
CH3
CH4
CH5
CH6
CH7
Figure 31. 2.051MHz Oscillator for 100sps Output Rate
270pF
1k
5k
SET
O
O
= 614.4kHz
= 2.048MHz
10k
8-CHANNEL
MUX
1
2N3904
10pF
MUXOUT
U1-A
1, 6, 16, 18, 22, 27, 28
47k
2
7
5pF
3
LTC2424/LTC2428
4
ADCIN
U1-B
+
–
4
47k
1k
20-BIT
GND
LTC2428
5V
ADC
3
FS
11
9
5
SET
U1-C
U1-E
U1-D
V
CC
24248 F31
2, 8
CSMUX
CSADC
10
6
8
SDO
SCK
CLK
24248 F32
D
TO LTC2424/
LTC2428
F
12
F
IN
O
O
PIN
U1-F
26
23
20
25
19
21
24
5V
13
29
V
1 F
CC
HALT