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參數(shù)資料
| 型號： | SPT7840SCS |
| 廠商： | SIGNAL PROCESSING TECHNOLOGIES |
| 元件分類： | ADC |
| 英文描述： | 1-CH 10-BIT SUCCESSIVE APPROXIMATION ADC, PARALLEL ACCESS, PDSO28 |
| 封裝： | SOIC-28 |
| 文件頁數(shù)： | 11/12頁 |
| 文件大?。?/td> | 96K |
| 代理商： | SPT7840SCS |
SPT
8
2/10/98
SPT7840
Figure 2 - Ladder Force/Sense Circuit
R/2
R
R/2
R=30
(typ)
All capacitors are 0.01 F
VRLF (AGND)
0.0 V
VRLS
(0.075 V)
VRHS
(+3.91 V)
90 mV
75 mV
+4.0 V
External
Reference
Figure 3 - Reference Ladder
AGND
VRHF
VRHS
VRLS
VRLF
VIN
1
2
3
5
6
7
+
-
+
-
All capacitors are 0.01 F
4
N/C
In cases where wider variations in offset and gain can be
tolerated, VRef can be tied directly to VRHF and AGND can be
tied directly to VRLF as shown in figure 3. Decouple force and
sense lines to AGND with a .01
F capacitor (chip cap
preferred) to minimize high-frequency noise injection. If this
simplified configuration is used, the following considerations
should be taken into account:
The reference ladder circuit shown in figure 3 is a simplified
representation of the actual reference ladder with force and
sense taps shown. Due to the actual internal structure of the
ladder, the voltage drop from VRHF to VRHS is not equivalent
to the voltage drop from VRLF to VRLS.
Typically, the top side voltage drop for VRHF to VRHS will
equal:
VRHF - VRHS = 2.25% of (VRHF - VRLF) (typical),
and the bottom side voltage drop for VRLS to VRLF will equal:
VRLS - VRLF = 1.9% of (VRHF - VRLF) (typical).
Figure 3 shows an example of expected voltage drops for a
specific case. VRef of 4.0 V is applied to VRHF and VRLF is
tied to AGND. A 90 mV drop is seen at VRHS (= 3.91 V) and
a 75 mV increase is seen at VRLS (= 0.075 V).
ANALOG INPUT
VIN is the analog input. The input voltage range is from VRLS to
VRHS (typically 4.0 V) and will scale proportionally with respect
to the voltage reference. (See voltage reference section.)
The drive requirements for the analog inputs are very minimal
when compared to most other converters due to the SPT7840's
extremely low input capacitance of only 5 pF and very high
input resistance of 50 k
.
The analog input should be protected through a series
resistor and diode clamping circuit as shown in figure 4.
CALIBRATION
The SPT7840 uses an auto calibration scheme to ensure 10-
bit accuracy over time and temperature. Gain and offset
errors are continually adjusted to 10-bit accuracy during
device operation. This process is completely transparent to
the user.
Upon power-up, the SPT7840 begins its calibration algo-
rithm. In order to achieve the calibration accuracy required,
the offset and gain adjustment step size is a fraction of a 10-
bit LSB. Since the calibration algorithm is an oversampling
process, a minimum of 10k clock cycles are required. This
results in a minimum calibration time upon power-up of
500
sec (for a 10 MHz sample rate). Once calibrated, the
SPT7840 remains calibrated over time and temperature.
Since the calibration cycles are initiated on the rising edge of
the clock, the clock must be continuously applied for the
SPT7840 to remain in calibration.
INPUT PROTECTION
All I/O pads are protected with an on-chip protection circuit
shown in figure 5. This circuit provides ESD robustness to
3.5 kV and prevents latch-up under severe discharge condi-
tions without degrading analog transition times.
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| SPT7840SCT | 制造商:FAIRCHILD 制造商全稱:Fairchild Semiconductor 功能描述:10-BIT, 10 MSPS, 100 mW A/D CONVERTER |
| SPT7840SIS | 制造商:FAIRCHILD 制造商全稱:Fairchild Semiconductor 功能描述:10-BIT, 10 MSPS, 100 mW A/D CONVERTER |
| SPT7850 | 制造商:FAIRCHILD 制造商全稱:Fairchild Semiconductor 功能描述:10-BIT, 20 MSPS, 140 mW A/D CONVERTER |
| SPT7850SCN | 制造商:FAIRCHILD 制造商全稱:Fairchild Semiconductor 功能描述:10-BIT, 20 MSPS, 140 mW A/D CONVERTER |
| SPT7850SCT | 制造商:CADEKA 制造商全稱:CADEKA 功能描述:10-BIT, 20 MSPS, 140 mW A/D CONVERTER |
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