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參數資料
| 型號： | DC570A |
| 廠商： | Linear Technology |
| 文件頁數： | 16/28頁 |
| 文件大?。?/td> | 0K |
| 描述： | BOARD DELTA SIGMA ADC LTC2440 |
| 軟件下載： | QuikEval System |
| 設計資源： | DC570A Design File DC570A Schematic |
| 標準包裝： | 1 |
| 系列： | QuikEval™ |
| ADC 的數量： | 2 |
| 位數： | 24 |
| 采樣率（每秒）： | 3.5k |
| 數據接口： | MICROWIRE?，串行，SPI? |
| 工作溫度： | 0°C ~ 70°C |
| 已用 IC / 零件： | LTC2440 |
| 已供物品： | 板 |
| 相關產品： | LTC2440CGN#TRPBF-ND - IC ADC DIFFER 24-BIT HS 16-SSOP LTC2440IGN#TRPBF-ND - IC ADC DIFFER 24-BIT HS 16-SSOP LTC2440IGN#PBF-ND - IC ADC DIFFER 24-BIT HS 16-SSOP LTC2440CGN#PBF-ND - IC ADC DIFFER 24-BIT HS 16-SSOP LTC2440IGN#TR-ND - IC CONV A/D 24-BIT DIFF 16-SSOP LTC2440CGN#TR-ND - IC CONV A/D 24-BIT DIFF 16-SSOP LTC2440IGN-ND - IC ADC DIFFER 24-BIT HS 16-SSOP LTC2440CGN-ND - IC ADC DIFFER 24-BIT HS 16-SSOP |
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LTC2440
23
2440fd
APPLICATIONS INFORMATION
Figure 18. Input Capacitors Allow Longer Connection
Between the Low Impedance Source and the ADC.
Direct Connection to Low Impedance Sources
If the ADC can be located physically close to the sensor,
it can be directly connected to sensors or other sources
with impedances up to 350Ω with no other components
required (see Figure 17).
Longer Connections to Low Impedance Sources
If longer lead lengths are unavoidable, adding an input
capacitor close to the ADC input pins will average the
charging pulses and prevent reections or ringing (see
Figure 18). Averaging the current pulses results in a DC
input current that should be taken into account. The re-
sulting 110kΩ input impedance will result in a gain error
of 0.44% for a 350Ω bridge (within the full scale specs
of many bridges) and a very low 12.6ppm error for a 2Ω
thermocouple connection.
Buffering the LTC2440
Many applications will require buffering, particularly
where high impedance sources are involved or where the
device being measured is located some distance from the
LTC2440. When buffering the LTC2440 a few simple steps
should be followed.
Figure 19 shows a network suitable for coupling the inputs
of a LTC2440 to a LTC2051 chopper-stabilized op amp. The
3μV offset and low noise of the LTC2051 make it a good
choice for buffering the LTC2440. Many other op amps
will work, with varying performance characteristics.
The LTC2051 is congured to be able to drive the 1μF ca-
pacitors at the inputs of the LTC2440. The 1μF capacitors
should be located close to the ADC input pins.
The measured total unadjusted error of Figure 19 is well
within the specications of the LTC2440 by itself. Most
autozero ampliers will degrade the overall resolution to
some degree because of the extremely low input noise
of the LTC2440, however the LTC2051 is a good general
purpose buffer. The measured input referred noise of two
LTC2051s buffering both LTC2440 inputs is approximately
double that of the LTC2440 by itself, which reduces the ef-
fective resolution by 1-bit for all oversample ratios. Adding
gain to the LTC2051 will increase gain and offset errors
and will not appreciably increase the overall resolution,
so it has limited benet.
Procedure For Coupling Any Amplier to the LTC2440
The LTC2051 is suitable for a wide range of DC and low
frequency measurement applications. If another ampli-
er is to be selected, a general procedure for evaluating
the suitability of an amplier for use with the LTC2440 is
suggested here:
1. Perform a thorough error and noise analysis on the
amplier and gain setting components to verify that the
amplier will perform as intended.
2. Measure the large signal response of the overall circuit.
The capacitive load may affect the maximum slew rate of
the amplier. Verify that the slew rate is adequate for the
Figure 17. Direct Connection to Low Impedance (<350Ω) Source
is Possible if the Sensor is Located Close to the ADC.
2440 F17
REF+
REF–
IN+
IN–
LTC2440
1μF
4.5V to 5.5V
2440 F18
1μF
4.5V to 5.5V
REMOTE
THERMOCOUPLE
VREF+ VCC
GND
IN+
IN–
LTC2440
1μF
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