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参数资料
| 型号： | DC1009A-A |
| 厂商： | Linear Technology |
| 文件页数： | 20/36页 |
| 文件大小： | 0K |
| 描述： | BOARD DELTA SIGMA ADC LTC2492 |
| 软件下载： | QuikEval System |
| 设计资源： | DC1009A Design File DC1009A Schematic |
| 标准包装： | 1 |
| 系列： | Easy Drive™, QuikEval™ |
| ADC 的数量： | 1 |
| 位数： | 24 |
| 采样率（每秒）： | 7.5 |
| 数据接口： | MICROWIRE?，串行，SPI? |
| 已用 IC / 零件： | LTC2492 |
| 已供物品： | 板 |
| 相关产品： | LTC2492CDE#TRPBF-ND - IC ADC 24BIT DELTA SIG 14-DFN LTC2492IDE#TRPBF-ND - IC ADC 24BIT DELTA SIG 14-DFN LTC2492IDE#PBF-ND - IC ADC 24BIT DELTA SIG 14-DFN LTC2492CDE#PBF-ND - IC ADC 24BIT DELTA SIG 14-DFN |
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LTC2492
27
2492fd
APPLICATIONS INFORMATION
Driving the Input and Reference
The input and reference pins of the LTC2492 are connected
directly to a switched capacitor network. Depending on
the relationship between the differential input voltage and
the differential reference voltage, these capacitors are
switched between these four pins. Each time a capacitor
is switched between two of these pins, a small amount
of charge is transferred. A simplied equivalent circuit is
shown in Figure 12.
When using the LTC2492’s internal oscillator, the input
capacitor array is switched at 123kHz. The effect of the
charge transfer depends on the circuitry driving the input/
reference pins. If the total external RC time constant is less
than 580ns the errors introduced by the sampling process
are negligible since complete settling occurs.
Typically, the reference inputs are driven from a low
impedance source. In this case, complete settling occurs
even with large external bypass capacitors. The inputs (CH0
to CH3, COM), on the other hand, are typically driven from
larger source resistances. Source resistances up to 10k
may interface directly to the LTC2492 and settle completely;
however, the addition of external capacitors at the input
terminals in order to lter unwanted noise (anti-aliasing)
results in incomplete settling.
Automatic Differential Input Current Cancellation
In applications where the sensor output impedance is
low (up to 10kΩ with no external bypass capacitor or up
to 500Ω with 0.001μF bypass), complete settling of the
input occurs. In this case, no errors are introduced and
direct digitization is possible.
For many applications, the sensor output impedance
combined with external input bypass capacitors produces
RC time constants much greater than the 580ns required
for 1ppm accuracy. For example, a 10kΩ bridge driving a
0.1μF capacitor has a time constant an order of magnitude
greater than the required maximum.
TheLTC2492usesaproprietaryswitchingalgorithmthatforces
the average differential input current to zero independent of
external settling errors. This allows direct digitization of high
impedance sensors without the need of buffers.
The switching algorithm forces the average input current
on the positive input (IIN+) to be equal to the average input
current on the negative input (IIN–). Over the complete
Figure 12. LTC2492 Equivalent Analog Input Circuit
IN+
IN–
10k
INTERNAL
SWITCH
NETWORK
10k
CEQ
12pF
10k
IIN
–
REF+
IREF
+
IIN
+
IREF
–
2492 F12
SWITCHING FREQUENCY
fSW = 123kHz INTERNAL OSCILLATOR
fSW = 0.4 fEOSC EXTERNAL OSCILLATOR
REF–
10k
100Ω
INPUT
MULTIPLEXER
100Ω
IIN
I IN
VV
R
AVG
IN CM
REF CM
EQ
+
() = () =
–
()
.
05
IIREF
VV
V
R
AVG
REF
REF CM
IN CM
+
() ≈
+
()
15
05
.–
.
()
E
EQ
IN
REF
EQ
REF
REF CM
V
VR
where
V
REF
V
–
:
(
2
=
+
))
–
,
=
=
+
REF
V
IN
WHERE IN AN
IN
2
D
D IN ARE THE SELECTED INPUT CHANNELS
V
IN
IN CM
+
=
()
–
.
IN
R
M INTERNAL OSCILLATOR
EQ
=
2
271
6
Ω
0
0Hz MODE
R
2.98M INTERNAL OSCILLATOR 50Hz/60
EQ =Ω
H
Hz MODE
R0.833 10
/f
EXTERNAL OSCIL
EQ
12
EOSC
=
()
L
LATOR
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