A suggestion is to tie CONVST to VDD or DGN" />
參數(shù)資料
型號(hào): AD7825BRZ-REEL
廠商: Analog Devices Inc
文件頁(yè)數(shù): 3/28頁(yè)
文件大?。?/td> 0K
描述: IC ADC 8BIT 4CH 2MSPS 24-SOIC
標(biāo)準(zhǔn)包裝: 1,000
位數(shù): 8
采樣率(每秒): 2M
數(shù)據(jù)接口: 并聯(lián)
轉(zhuǎn)換器數(shù)目: 1
功率耗散(最大): 36mW
電壓電源: 單電源
工作溫度: -40°C ~ 85°C
安裝類型: 表面貼裝
封裝/外殼: 24-SOIC(0.295",7.50mm 寬)
供應(yīng)商設(shè)備封裝: 24-SOIC W
包裝: 帶卷 (TR)
輸入數(shù)目和類型: 4 個(gè)單端,單極
AD7822/AD7825/AD7829
Rev. C | Page 11 of 28
A suggestion is to tie CONVST to VDD or DGND through a pull-up
or pull-down resistor. A rising edge on the CONVST pin causes
the AD7829 to fully power up, while a rising edge on the PD pin
causes the AD7822 and AD7825 to fully power up. For applica-
tions where power consumption is of concern, the automatic
power-down at the end of a conversion should be used to improve
power performance (see the Power vs. Throughput section).
SUPPLY
4.5V TO 5.5V
10F
0.1F
VDD
VREF
VMID
VIN1
1.25V TO
3.75V INPUT
VIN24
VIN4(VIN85)
AGND
DB0 TO DB7
EOC
RD
CS
CONVST
A01
A11
A22
PD3
PARALLEL
INTERFACE
C/P
AD7822/
AD7825/
AD7829
DGND
2.5V
AD780
01
32
1-
0
09
1A0, A1
AD7825/AD7829
2A2
AD7829
3PD
AD7822/AD7825
4VIN2 TO VIN4
AD7825/AD7829
5VIN5 TO VIN8
AD7829
Figure 9. Typical Connection Diagram
ADC TRANSFER FUNCTION
The output coding of the AD7822/AD7825/AD7829 is straight
binary. The designed code transitions occur at successive integer
LSB values (that is, 1 LSB, 2 LSBs, and so on). The LSB size =
VREF/256 (VDD = 5 V) or the LSB size = (0.8 VREF)/256 (VDD =
3 V). The ideal transfer characteristic for the AD7822/AD7825/
AD7829 is shown in Figure 10.
11111111
111...110
111...000
10000000
000...111
000...010
00000000
(VDD = 5V)
1LSB = VREF/256
(VDD = 3V)
1LSB = 0.8VREF/256
000...001
AD
C
CO
DE
1LSB
VMID
(VDD = 5V) VMID – 1.25V
(VDD = 3V) VMID – 1V
VMID + 1.25V – 1LSB
VMID + 1V – 1LSB
ANALOG INPUT VOLTAGE
0
13
21
-01
0
Figure 10. Transfer Characteristic
ANALOG INPUT
The AD7822 has a single input channel, and the AD7825 and
AD7829 have four and eight input channels, respectively. Each
input channel has an input span of 2.5 V or 2.0 V, depending on
the supply voltage (VDD). This input span is automatically set up
by an on-chip VDD detector circuit. A 5 V operation of the ADCs
is detected when VDD exceeds 4.1 V, and a 3 V operation is
detected when VDD falls below 3.8 V. This circuit also possesses
a degree of glitch rejection; for example, a glitch from 5.5 V to
2.7 V up to 60 ns wide does not trip the VDD detector.
The VMID pin is used to center this input span anywhere in the
range of AGND to VDD. If no input voltage is applied to VMID,
the default input range is AGND to 2.0 V (VDD = 3 V ± 10%),
that is, centered about 1.0 V; or AGND to 2.5 V (VDD = 5 V ±
10%), that is, centered about 1.25 V. When using the default
input range, the VMID pin can be left unconnected, or in some
cases, it can be decoupled to AGND with a 0.1 μF capacitor.
If, however, an external VMID is applied, the analog input range
is from VMID 1.0 V to VMID + 1.0 V (VDD = 3 V ± 10%), or
from VMID 1.25 V to VMID + 1.25 V (VDD = 5 V ± 10%).
The range of values of VMID that can be applied depends on the
value of VDD. For VDD = 3 V ± 10%, the range of values that can
be applied to VMID is from 1.0 V to VDD 1.0 V and from 1.25 V to
VDD 1.25 V when VDD = 5 V ± 10%. Table 5 shows the relevant
ranges of VMID and the input span for various values of VDD.
Figure 11 illustrates the input signal range available with various
values of VMID.
Table 5.
VDD
VMID
Internal
VMID Ext
Max
VIN Span
VMID Ext
Min
VIN Span
Unit
5.5
1.25
4.25
3.0 to 5.5
1.25
0 to 2.5
V
5.0
1.25
3.75
2.5 to 5.0
1.25
0 to 2.5
V
4.5
1.25
3.25
2.0 to 4.5
1.25
0 to 2.5
V
3.3
1.00
2.3
1.3 to 3.3
1.00
0 to 2.0
V
3.0
1.00
2.0
1.0 to 3.0
1.00
0 to 2.0
V
2.7
1.00
1.7
0.7 to 2.7
1.00
0 to 2.0
V
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