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參數(shù)資料
| 型號： | 2495 |
| 廠商： | Linear Technology Corporation |
| 英文描述： | 16-Bit 8-/16-Channel ツヒ ADC with PGA, Easy Drive and I2C Interface |
| 中文描述： | 16位8-/16-ChannelツヒADC，帶PGA巡回賽，輕松驅(qū)動和I2C接口 |
| 文件頁數(shù)： | 23/32頁 |
| 文件大?。?/td> | 558K |
| 代理商： | 2495 |
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LTC2495
23
2495f
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-CH15, COM), on the other hand, are typically driven
from larger source resistances. Source resistances up
to 10k may interface directly to the LTC2495 and settle
completely; however, the addition of external capacitors
at the input terminals in order to filter unwanted noise
(antialiasing) results in incomplete settling.
The LTC2495 offers two methods of removing these
errors. The first is automatic differential input current
cancellation (Easy Drive) and the second is the insertion
of an external buffer between the MUXOUT and ADCIN
pins, thus isolating the input switching from the source
resistance.
Automatic Differential Input Current Cancellation
In applications where the sensor output impedance is
low (up to 10k
Ω
with no external bypass capacitor or up
to 500
Ω
with 0.001μF bypass), complete settling of the
Figure 11. Equivalent Analog Input Circuit
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 10k
Ω
bridge driving a
0.1μF capacitor has a time constant an order of magnitude
greater than the required maximum.
The LTC2495 uses a proprietary switching algorithm
that forces the average differential input current to zero
independent of external settling errors. This allows direct
digitization of high impedance sensors without the need
for buffers.
The switching algorithm forces the average input current
on the positive input (I
IN+
) to be equal to the average input
current on the negative input (I
IN–
). Over the complete
conversion cycle, the average differential input current
(I
IN+
– I
IN–
) is zero. While the differential input current is
zero, the common mode input current (I
IN+
+ I
IN–
)/2 is
proportional to the difference between the common mode
input voltage (V
IN(CM)
) and the common mode reference
voltage (V
REF(CM)
).
APPLICATIONS INFORMATION
IN+
IN
–
10k
INTERNAL
SWITCH
NETWORK
10k
C
EQ
12
μ
F
10k
I
IN–
REF
+
I
REF+
I
IN+
I
REF–
2495 F11
SWITCHING FREQUENCY
f
SW
= 123kHz INTERNAL OSCILLATOR
f
SW
= 0.4 f
EOSC
EXTERNAL OSCILLATOR
REF
–
10k
100
INPUT
MULTIPLEXER
EXTERNAL
CONNECTION
100
MUXOUTP
ADCINP
EXTERNAL
CONNECTION
MUXOUTN
ADCINN
I IN
I IN
V
V
R
AVG
)
:
AVG
IN CM
(
REF CM
(
EQ
V
+
)
=
)
=
–
)
)
.5
I REF
where
V
V
R
AVG
REF
REF CM
0 5
.
IN CM
(
+
≈
+
(
)
1 5
.
–
(
)
)
EQ
IN
REF
V
EQ
REF
V
REF CM
V
V
R
REF
REF
–
(
2
=
+
)
–
2
,
=
=
+
+
REF
REF
V
IN
IN
WHEREIN AN
2
IN
DIN ARE THE SELECTEDINPUT CHANNELS
V
IN
IN CM
(
+
=
)
–
.
IN
R
R
M INTERNAL OSCILLATOR
2 71
2.98M INTERNAL OSCILLATOR50Hz/60
(
EQ
EQ
=
R
EQ
=
6
0HzMODE
Hz MODE
0.833 10
/f
EXTERNAL OSCIL
12
EOSC
=
)
LATOR
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