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參數資料
| 型號： | AD7828 |
| 廠商： | Analog Devices, Inc. |
| 英文描述： | 2.7V-5.25V Digital, 5V Analog, 12 Bit, 4MSPS, Parallel ADC with Ref 48-TQFP -40 to 85 |
| 中文描述： | LC2MOS高速4 - |
| 文件頁數： | 6/16頁 |
| 文件大小： | 270K |
| 代理商： | AD7828 |
AD7824/AD7828
–6–
REV. F
OPERATIONAL DIAGRAM
The AD7824 is a 4-channel 8-bit ADC and the AD7828 is an
8-channel 8-bit ADC. Operational diagrams for both of these
devices are shown in Figures 3 and 4. The addition of just a 5 V
reference allows the devices to perform the analog-to-digital function.
24
23
22
21
20
19
18
17
16
15
14
13
1
2
3
4
5
6
7
8
9
10
11
12
AD7824
NC = NO CONNECT
AIN4
V
DD
NC
AIN3
AIN2
A0
AIN1
A1
NC
DB7
DB0
DB6
DB1
DB5
DB2
DB4
DB3
CS
RD
RDY
INT
V
REF
(+)
V
REF
(–)
GND
ANALOG INPUTS
0V TO 5V
P 4LSB
DATA BUS
P CONTROL INPUT
STATUS OUTPUT
P ADDRESS
BUS
P 4MSB
DATA BUS
P CONTROL INPUT
STATUS OUTPUT
5V
5V
Figure 3. AD7824 Operational Diagram
28
27
26
25
24
23
22
21
20
19
18
17
16
15
1
2
3
4
5
6
7
8
9
10
11
12
13
14
AD7828
NC = NO CONNECT
AIN6
AIN7
AIN5
AIN8
AIN4
V
DD
A0
AIN3
AIN2
A1
AIN1
A2
NC
DB7
DB0
DB6
DB1
DB5
DB2
DB4
DB3
CS
RD
RDY
INT
V
REF
(+)
V
REF
(–)
GND
ANALOG INPUTS
0V TO 5V
P 4LSB
DATA BUS
P CONTROL INPUT
STATUS OUTPUT
ANALOG INPUTS
0V TO 5V
P ADDRESS
BUS
P 4MSB
DATA BUS
P CONTROL INPUT
STATUS OUTPUT
5V
5V
Figure 4. AD7828 Operational Diagram
CIRCUIT INFORMATION
BASIC DESCRIPTION
The AD7824/AD7828 uses a half-flash conversion technique
whereby two 4-bit flash ADCs are used to achieve an 8-bit result.
Each 4-bit flash ADC contains 15 comparators that compare
the unknown input to a reference ladder to get a 4-bit result.
For a full 8-bit reading to be realized, the upper 4-bit flash, the
most significant (MS) flash, performs a conversion to provide
the four most significant data bits. An internal DAC, driven by
the four MSBs, then recreates an analog approximation of the
input voltage. This analog result is subtracted from the input,
and the difference is converted by the lower flash ADC, the least
significant (LS) flash, to provide the four least significant bits of
the output data. The most significant flash ADC also has one
additional comparator to detect overrange on the analog input.
APPLYING THE AD7824/AD7828
REFERENCE AND INPUT
The two reference inputs on the AD7824/AD7828 are fully differ-
ential and define the zero to full-scale input range of the ADC.
As a result, the span of the analog input voltage for all channels
can easily be varied. By reducing the reference span, V
REF
(+) to
V
REF
(–), to less than 5 V, the sensitivity of the converter can be
increased (e.g., if V
REF
= 2 V then 1 LSB = 7.8 mV). The input/
reference arrangement also facilitates ratiometric operation.
This reference flexibility also allows the input channel voltage
span to be offset from zero. The voltage at V
REF
(–) sets the
input level for all channels, which produces a digital output of
all zeroes. Therefore, although the analog inputs are not them-
selves differential, they have nearly differential input capability
in most measurement applications because of the reference
design. Figures 5 to 7 show some of the configurations that are
possible.
AD7824
*
AD7828
*
AIN1
GND
V
DD
V
REF
(+)
V
REF
(–)
47 F
0.1 F
V
IN
(–)
V
IN
(+)
5V
ADDITIONAL PINS OMITTED FOR CLARITY.
ONLY CHANNEL 1 SHOWN.
*
Figure 5. Power Supply as Reference
AD7824
*
AD7828
*
AIN1
GND
V
DD
V
REF
(+)
V
REF
(–)
47 F
0.1 F
V
IN
(–)
V
IN
(+)
5V
ADDITIONAL PINS OMITTED FOR CLARITY.
ONLY CHANNEL 1 SHOWN.
*
AD580
0.1 F
10 F
Figure 6. External Reference Using the AD580, Full-Scale
Input is 2.5 V
AD7824
*
AD7828
*
AIN1
GND
V
DD
V
REF
(+)
V
REF
(–)
47 F
0.1 F
V
IN
(+)
5V
ADDITIONAL PINS OMITTED FOR CLARITY.
ONLY CHANNEL 1 SHOWN.
*
DB7
DB0
DATA
V1
V2
DATA = V
IN
(+)
Figure 7. Input Not Referenced to GND
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