参数资料
型号: LTC1290CIJ#PBF
厂商: LINEAR TECHNOLOGY CORP
元件分类: ADC
英文描述: 8-CH 12-BIT SUCCESSIVE APPROXIMATION ADC, SERIAL ACCESS, CDIP20
封装: 0.300 INCH, LEAD FREE, HERMETIC SEALED, CERAMIC, DIP-20
文件页数: 13/32页
文件大小: 613K
代理商: LTC1290CIJ#PBF
20
LTC1290
1290fe
U
S
A
O
PPLICATI
WU
U
I FOR ATIO
4TH SCLK
RON = 500
LAST SCLK
CIN =
100pF
LTC1290
“+”
INPUT
RSOURCE +
VIN +
C1
“–”
INPUT
RSOURCE
VIN
C2
LTC1290 F09
Figure 9. Analog Input Equivalent Circuit
“+” Input Settling
This input capacitor is switched onto the “+” input during
the sample phase (tSMPL, see Figure 10). The sample
phase starts at the 4th SCLK cycle and lasts until the falling
edge of the last SCLK (the 8th, 12th or 16th SCLK cycle
depending on the selected word length). The voltage on
the “+” input must settle completely within this sample
time. Minimizing RSOURCE+ and C1 will improve the input
settling time. If large “+” input source resistance must be
used, the sample time can be increased by using a slower
SCLK frequency or selecting a longer word length. With
the minimum possible sample time of 2
s, RSOURCE+ < 1k
and C1 < 20pF will provide adequate settling.
“–” Input Settling
At the end of the sample phase the input capacitor switches
to the “–” input and the conversion starts (see Figure 10).
During the conversion, the “+” input voltage is effectively
“held” by the sample-and-hold and will not affect the
conversion result. However, it is critical that the “–” input
voltage be free of noise and settle completely during the
first four ACLK cycles of the conversion time. Minimizing
RSOURCE– and C2 will improve settling time. If large “–”
input source resistance must be used, the time allowed for
settling can be extended by using a slower ACLK fre-
quency. At the maximum ACLK rate of 4MHz, RSOURCE–
< 250
and C2 < 20pF will provide adequate settling.
Input Op Amps
When driving the analog inputs with an op amp it is
important that the op amp settle within the allowed time
(see Figure 10). Again, the “+” and “–” input sampling
times can be extended as described above to accommo-
date slower op amps. Most op amps including the LT1797,
LT1800 and LT1812 single supply op amps can be made
to settle well even with the minimum settling windows of
2
s (“+” input) and 1s (“–” input) which occur at the
SCLK
CS
“+” INPUT
ACLK
1290 F10
1
234
MUX ADDRESS
SHIFTED IN
tSMPL
LAST SCLK (8TH, 12TH OR 16TH DEPENDING ON WORD LENGTH)
1
234
1ST BIT TEST
“–” INPUT MUST SETTLE
DURING THIS TIME
SAMPLE
HOLD
“+” INPUT
MUST SETTLE
DURING THIS TIME
“–” INPUT
Figure 10. “+” and “–” Input Settling Windows
相关PDF资料
PDF描述
LTC1290DMJ#TR 8-CH 12-BIT SUCCESSIVE APPROXIMATION ADC, SERIAL ACCESS, CDIP20
LTC1290DMJ#TRPBF 8-CH 12-BIT SUCCESSIVE APPROXIMATION ADC, SERIAL ACCESS, CDIP20
LTC1290CIN#TR 8-CH 12-BIT SUCCESSIVE APPROXIMATION ADC, SERIAL ACCESS, PDIP20
LTC1290DCN#TRPBF 8-CH 12-BIT SUCCESSIVE APPROXIMATION ADC, SERIAL ACCESS, PDIP20
LTC1290CIN#TRPBF 8-CH 12-BIT SUCCESSIVE APPROXIMATION ADC, SERIAL ACCESS, PDIP20
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