Datasheet LTC2424, LTC2428 (Analog Devices) - 29
| Fabricante | Analog Devices |
| Descripción | 4-/8-Channel 20-Bit µPower No Latency ∆ΣTM ADCs |
| Páginas / Página | 36 / 29 — APPLICATIONS INFORMATION. Figure 30. Low Power Reference. 2.051MHz … |
| Formato / tamaño de archivo | PDF / 431 Kb |
| Idioma del documento | Inglés |
APPLICATIONS INFORMATION. Figure 30. Low Power Reference. 2.051MHz Oscillator for 100sps Output Ratio
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LTC2424/LTC2428
U U W U APPLICATIONS INFORMATION
1k TO Consecutive readings are performed on each side of the 5V IN OUT LTC2424/LTC2428 + 10µF FS 0.1µF SET bridge by selecting the appropriate channel on the LT1461-2.5 16V CER TANT LTC2428. Each output is digitized and the results digitally GND subtracted to obtain the pseudodifferential result. Several 24248 F30 bridge transducers may be digitized in this manner. In order to measure absolute temperature with a thermo-
Figure 30. Low Power Reference
couple, cold junction compensation must be performed. Channel 6 measures the output of the thermocouple while than 60% full scale, and only marginally increases noise channel 7 measures the output of the cold junction sensor approaching full scale. Even lower power references can (diode, thermistor, etc.). This enables digital cold junction be used if only the lower end of the LTC2424/LTC2428 compensation of the thermocouple output. The tempera- input range is required. ture measurement may then be used to compensate the
2.051MHz Oscillator for 100sps Output Ratio
temperature effects of the bridge transducers. The oscillator circuit shown in Figure 31 can be used to drive the F 1k 10k 1k O pin, boosting the conversion rate of the U1-F LTC2420 for applications that do not require a notch at 50 47k 12 13 2N3904 HALT or 60Hz. This oscillator is not sensitive to hysteresis voltage of a Schmitt trigger device as are simpler 5k 47k relaxation oscillators using the 74HC14 or similar de- 5pF 270pF vices. The circuit can be tuned over a 3-1 range with only U1-A U1-B U1-C one resistor and can be gated. The use of transmission 1 2 3 4 5 6 gates could be used to shift the frequency in order to 10pF U1-E provide setable conversion rates. 11 10
Pseudodifferential Multichannel Bridge Digitizer and
U1-D 100smps, FO = 2.048MHz TO LTC2424/ 9 8
Digital Cold Junction Compensation
30smps, FO = 614.4kHz LTC2428 U1: 74HC14 OR EQUIVALENT 24248 F31 FO PIN The circuit shown in Figure 32 enables pseudodifferential measurements of several bridge transducers and abso- lute temperature measurement.
Figure 31. 2.051MHz Oscillator for 100sps Output Rate
5V 5V 7 4 3 2, 8 1µF MUXOUT ADCIN FSSET VCC THERMOCOUPLE 9 CH0 10 CH1 23 CSADC 11 CH2 20 CSMUX THERMISTOR 12 CH3 25 20-BIT SCK 8-CHANNEL 13 CH4 + 19 ∆Σ ADC MUX CLK 14 CH5 21 DIN – 15 CH6 24 SDO 17 CH7 LTC2428 VCC 5 ZSSET 26 GND FO 24248 F32 1, 6, 16, 18, 22, 27, 28
Figure 32. Pseudodifferential Multichannel Bridge Digitizer and Digital Cold Junction Compensation
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U U W U APPLICATIONS INFORMATION
1k TO Consecutive readings are performed on each side of the 5V IN OUT LTC2424/LTC2428 + 10µF FS 0.1µF SET bridge by selecting the appropriate channel on the LT1461-2.5 16V CER TANT LTC2428. Each output is digitized and the results digitally GND subtracted to obtain the pseudodifferential result. Several 24248 F30 bridge transducers may be digitized in this manner. In order to measure absolute temperature with a thermo-
Figure 30. Low Power Reference
couple, cold junction compensation must be performed. Channel 6 measures the output of the thermocouple while than 60% full scale, and only marginally increases noise channel 7 measures the output of the cold junction sensor approaching full scale. Even lower power references can (diode, thermistor, etc.). This enables digital cold junction be used if only the lower end of the LTC2424/LTC2428 compensation of the thermocouple output. The tempera- input range is required. ture measurement may then be used to compensate the
2.051MHz Oscillator for 100sps Output Ratio
temperature effects of the bridge transducers. The oscillator circuit shown in Figure 31 can be used to drive the F 1k 10k 1k O pin, boosting the conversion rate of the U1-F LTC2420 for applications that do not require a notch at 50 47k 12 13 2N3904 HALT or 60Hz. This oscillator is not sensitive to hysteresis voltage of a Schmitt trigger device as are simpler 5k 47k relaxation oscillators using the 74HC14 or similar de- 5pF 270pF vices. The circuit can be tuned over a 3-1 range with only U1-A U1-B U1-C one resistor and can be gated. The use of transmission 1 2 3 4 5 6 gates could be used to shift the frequency in order to 10pF U1-E provide setable conversion rates. 11 10
Pseudodifferential Multichannel Bridge Digitizer and
U1-D 100smps, FO = 2.048MHz TO LTC2424/ 9 8
Digital Cold Junction Compensation
30smps, FO = 614.4kHz LTC2428 U1: 74HC14 OR EQUIVALENT 24248 F31 FO PIN The circuit shown in Figure 32 enables pseudodifferential measurements of several bridge transducers and abso- lute temperature measurement.
Figure 31. 2.051MHz Oscillator for 100sps Output Rate
5V 5V 7 4 3 2, 8 1µF MUXOUT ADCIN FSSET VCC THERMOCOUPLE 9 CH0 10 CH1 23 CSADC 11 CH2 20 CSMUX THERMISTOR 12 CH3 25 20-BIT SCK 8-CHANNEL 13 CH4 + 19 ∆Σ ADC MUX CLK 14 CH5 21 DIN – 15 CH6 24 SDO 17 CH7 LTC2428 VCC 5 ZSSET 26 GND FO 24248 F32 1, 6, 16, 18, 22, 27, 28
Figure 32. Pseudodifferential Multichannel Bridge Digitizer and Digital Cold Junction Compensation
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