參數(shù)資料
型號: LTC1290DIJ
廠商: LINEAR TECHNOLOGY CORP
元件分類: ADC
英文描述: Single Chip 12-Bit Data Acquisition System
中文描述: 8-CH 12-BIT SUCCESSIVE APPROXIMATION ADC, SERIAL ACCESS, CDIP20
封裝: 0.300 INCH, HERMETIC SEALED, CERDIP-20
文件頁數(shù): 18/28頁
文件大?。?/td> 381K
代理商: LTC1290DIJ
18
LTC 1290
U
S
A
O
PPLICATI
W
U
I FOR ATIO
U
V
0.1
μ
F
CERAMIC
DISK
22
μ
F
TANTALUM
V
CC
LTC1290 F06
ANALOG
GROUND
PLANE
1
10
20
Figure 6. Example Ground Plane for the LTC1290
Figure 6 shows an example of an ideal ground plane design
for a two-sided board. Of course, this much ground plane
will not always be possible, but users should strive to get
as close to this ideal as possible.
2. Bypassing
For good performance, V
CC
must be free of noise and
ripple. Any changes in the V
CC
voltage with respect to
analog ground during a conversion cycle can induce
errors or noise in the output code. V
CC
noise and ripple can
be kept below 0.5mV by bypassing the V
CC
pin directly to
the analog ground plane with a 22
μ
F tantalum capacitor
and leads as short as possible. The lead from the device to
the V
CC
supply should also be kept to a minimum and the
V
CC
supply should have a low output impedance such as
that obtained from a voltage regulator (e.g., LT323A).
Figures 7 and 8 show the effects of good and poor V
CC
bypassing.
3. Analog Inputs
Because of the capacitive redistribution A/D conversion
techniques used, the analog inputs of the LTC1290 have
capacitive switching input current spikes. These current
Figure 7. Poor V
CC
Bypassing.
Noise and Ripple Can Cause A/D Errors
V
HORIZONTAL: 10
μ
s/DIV
CS
V
CC
Figure 8. Good V
CC
Bypassing Keeps
Noise and Ripple on V
CC
Below 1mV
HORIZONTAL: 10
μ
s/DIV
V
spikes settle quickly and do not cause a problem. How-
ever, if large source resistances are used or if slow settling
op amps drive the inputs, care must be taken to insure that
the transients caused by the current spikes settle com-
pletely before the conversion begins.
Source Resistance
The analog inputs of the LTC1290 look like a 100pF
capacitor (C
IN
) in series with a 500
resistor (R
ON
) as
shown in Figure 9.
C
IN
gets switched between the selected
“+” and “–” inputs once during each conversion cycle. Large
external source resistors and capacitances will slow the
settling of
the inputs. It is important that the overall RC time
constants be short enough to allow the analog inputs to
completely settle within the allowed time.
相關(guān)PDF資料
PDF描述
LTC1290DIN Single Chip 12-Bit Data Acquisition System
LTC1290DM Single Chip 12-Bit Data Acquisition System
LTC1290DMJ Single Chip 12-Bit Data Acquisition System
LTC1290 Single Chip 12-Bit Data Acquisition System
LTC1290BC Single Chip 12-Bit Data Acquisition System
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