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參數(shù)資料
| 型號： | DC956A |
| 廠商： | Linear Technology |
| 文件頁數(shù)： | 14/40頁 |
| 文件大?。?/td> | 0K |
| 描述： | BOARD DELTA SIGMA ADC LTC2485 |
| 軟件下載： | QuikEval System |
| 設計資源： | DC956A Design File DC956A Schematic |
| 標準包裝： | 1 |
| 系列： | Easy Drive™, QuikEval™ |
| ADC 的數(shù)量： | 1 |
| 位數(shù)： | 24 |
| 采樣率（每秒）： | 6.8 |
| 數(shù)據(jù)接口： | I²C，串行 |
| 工作溫度： | 0°C ~ 70°C |
| 已用 IC / 零件： | LTC2485 |
| 已供物品： | 板 |
| 相關產(chǎn)品： | LTC2485CDD#TRPBF-ND - IC ADC 24BIT I2C 10-DFN LTC2485IDD#TRPBF-ND - IC ADC 24BIT I2C 10-DFN LTC2485IDD#PBF-ND - IC ADC 24BIT I2C 10-DFN LTC2485CDD#PBF-ND - IC ADC 24BIT I2C 10-DFN |
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LTC2485
21
2485fc
APPLICATIONS INFORMATION
Reference Voltage Range
The LTC2485 external reference voltage range is 0.1V
to VCC. The converter output noise is determined by the
thermal noise of the front-end circuits, and as such, its
value in nanovolts is nearly constant with reference voltage.
A reduced reference voltage will improve the converter
performance when operated with an external conversion
clock (external fO signal) at substantially higher output
data rates (see the Output Data Rate section). VREF must
be ≥1.1V to use the internal temperature sensor.
The reference input is differential. The differential reference
input range (VREF = REF+ – REF–) is 100mV to VCC and the
common mode reference input range is 0V to VCC.
Input Voltage Range
The analog input is truly differential with an absolute/
common mode range for the IN+ and IN– input pins
extending from GND – 0.3V to VCC + 0.3V. Outside
these limits, the ESD protection devices begin to turn on
and the errors due to input leakage current increase rapidly.
Within these limits, the LTC2485 converts the bipolar differ-
ential input signal, VIN = IN+ – IN–, from –FS to +FS where
FS = 0.5 VREF. Beyond this range, the converter indicates
the overrange or the underrange condition using distinct
output codes. Since the differential input current cancella-
tion does not rely on an on-chip buffer, current cancellation
and DC performance is maintained rail-to-rail.
Input signals applied to IN+ and IN– pins may extend by
300mV below ground and above VCC. In order to limit any
fault current, resistors of up to 5k may be added in series
with the IN+ and IN– pins without affecting the performance
of the devices. The effect of the series resistance on the
converter accuracy can be evaluated from the curves
presented in the Input Current/Reference Current sections.
In addition, series resistors will introduce a temperature
dependent offset error due to the input leakage current.
A 1nA input leakage current will develop a 1ppm offset
error on a 5k resistor if VREF = 5V. This error has a very
strong temperature dependency.
Driving the Input and Reference
The input and reference pins of the LTC2485 converter
are directly connected to a network of sampling capaci-
tors. Depending upon the relation between the differential
input voltage and the differential reference voltage, these
capacitors are switching between these four pins transfer-
ring small amounts of charge in the process. A simplied
equivalent circuit is shown in Figure 12.
Figure 12. LTC2485 Equivalent Analog Input Circuit
VREF
+
VIN
+
VCC
RSW (TYP)
10k
ILEAK
VCC
ILEAK
VCC
RSW (TYP)
10k
CEQ
12pF
(TYP)
RSW (TYP)
10k
ILEAK
IIN
+
VIN
–
IIN
–
IREF
+
IREF
–
2485 F12
ILEAK
VCC
ILEAK
SWITCHING FREQUENCY
fSW = 123kHz INTERNAL OSCILLATOR
fSW = 0.4 fEOSC EXTERNAL OSCILLATOR
VREF
–
RSW (TYP)
10k
IIN
I IN
VV
R
I REF
VV
V
R
V
VR
VD
R
VV
V
R
V
VR
where
AVG
IN CM
REF CM
EQ
AVG
REF
INCM
REFCM
EQ
IN
REF
EQ
REF
T
EQ
REF
REF CM
IN CM
EQ
IN
REF
EQ
REF
REF–
–
()
.
.–
.
–
05
15
05
15
05
2
:
.
V
VIN
IN
V
IN
R
MΩ INTERNAL OSCILLATOR
Hz MODE
REFCM
IN
INCM
EQ
V
, REF
REF
REF–
2
271
60
R
2.98MΩ INTERNAL OSCILLATOR 50Hz AND 60Hz MODE
R
0.833 10
/ f
EXTERNAL OSCILLATOR
D IS THE DENSITY OF A DIGITAL TRANSITION AT THE MODULATOR OUTPUT
EQ
12
EOSC
T
WHERE REF– IS INTERNALLY TIED TO GND
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