the ADC range (V
參數(shù)資料
型號(hào): EVAL-AD7767-2EDZ
廠商: Analog Devices Inc
文件頁數(shù): 14/25頁
文件大小: 0K
描述: BOARD EVALUATION FOR AD7767
標(biāo)準(zhǔn)包裝: 1
ADC 的數(shù)量: 1
位數(shù): 24
采樣率(每秒): 32k
數(shù)據(jù)接口: 串行
輸入范圍: ±VREF
在以下條件下的電源(標(biāo)準(zhǔn)): 8.5mW @ 32kSPS
工作溫度: -40°C ~ 105°C
已用 IC / 零件: AD7767-2
已供物品: 板,CD
其它名稱: Q3407966
AD7767
Rev. C | Page 20 of 2
4
DRIVING THE AD7767
R1 and R2 set the attenuation ratio between the input range and
the ADC range (VREF). R1, R2, and CF are chosen depending on
the desired input resistance, signal bandwidth, antialiasing, and
noise contribution. The ratio of R2 to R1 should be equal to the
ratio of REF to the peak-to-peak input voltage. For example, for
the ±10 V range with a 4 kΩ impedance, R2 = 1 kΩ and R1 = 4 kΩ.
The AD7767 must be driven with fully differential inputs. The
common-mode voltage of the differential inputs to the AD7767
device and therefore the limits on the differential inputs are set
by the reference voltage (VREF) applied to the device. The common-
mode voltage of the AD7767 is VREF/2. When the AD7767 VREF+ pin
has a 5 V supply (using ADR445, ADR435, or ADR425), the
common mode is at 2.5 V, meaning that the maximum inputs that
can be applied on the AD7767 differential inputs are a 5 V p-p
input around 2.5 V.
R3 and R4 set the common mode on the IN input, and R5 and R6
set the common mode on the IN+ input of the ADC. The common
mode, which is equal to the voltage present at VOFFSET1, should be
close to VREF/2. The voltage present should roughly be set to the
ratio of VOFFSET1 to 1 + R2/R1.
06
85
9-
01
6
0V
VIN+
VIN–
VREF
2
0V
VREF
2
06
85
9-
02
0
ADA4841-1
15
3.3nF
1k
ADA4841-1
15
3.3nF
1k
4
5
1
2
AD7767
AVDD
VREF+
VIN+
VIN–
2.2nF
*
ADR4xx
ADP3330-2.5
2.5V
2.5V TO 5V
REFERENCE
VOLTAGE
1k
1k
1k
1k
AIN+
AIN–
*SEE VREF+ INPUT SIGNAL SECTION FOR DETAILS.
Figure 39. Maximum Differential Inputs to the AD7767
An analog voltage of 2.5 V supplies the AD7767 AVDD pin.
However, the AD7767 allows the user to apply a reference
voltage of up to 5 V. This provides the user with an increased
full-scale range, offering the user the option of using the
AD7767 with a greater LSB voltage. Figure 39 shows the
maximum inputs to the AD7767.
Figure 40. Driving the AD7767 from a Fully Differential Source
15
15
100F
R1
100nF
2.5V
VOUT = 5V REF
5.2V
–0.2V
CF
R4
R2
R6
Vin
R3
R5
VREF+
AVDD
AGND
VIN+
VIN–
AD7767
2.2nF
ADA4941
IN
FB
OUTP
OUTN
REF
Voffset1
Voffset2
ADR425
ADR445
VIN
ADP3330-2.5
LDO
DGND
0.1F
06
85
9-
018
DIFFERENTIAL SIGNAL SOURCE
An example of recommended driving circuitry that can be used
in conjunction with the AD7767/AD7767-1/AD7767-2 is shown in
Figure 40. Figure 40 shows how the ADA4841-1 device can be
used to drive an input to the AD7767/AD7767-1/AD7767-2
from a differential source. Each of the differential paths is
driven by an ADA4841-1 device.
SINGLE-ENDED SIGNAL SOURCE
For applications using a single-ended analog signal, either
bipolar or unipolar, the ADA4941-1 single-ended-to-differential
driver creates a fully differential input to the AD7767/AD7767-1/
AD7767-2. The schematic is shown in Figure 41.
Figure 41. Driving the AD7767 from a Single-Ended Source
Table 8. Resistor Values Required When Using the Differential to Single-Ended Circuit with ADA4941 (See Figure 41)
VIN (V)
VOFFSET1 (V)
VOFFSET2 (V)
OUT+ (V)
OUT (V)
R1 (kΩ)
R2 (kΩ)
R4 (kΩ)
R3 = R5 = R6 (kΩ)
+20, 20
2.5
2.203
0.01, +4.96
5.01, 0.04
8.06
1
12.7
10
+10, 10
2.5
2.000
0.01, 4.99
4.99, 0.01
4.02
1
15
10
+5, 5
2.5
1.667
0.00, 5.00
5.00, 0.00
2
1
20
10
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