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參數(shù)資料
| 型號： | AD7450BRMZ |
| 廠商： | Analog Devices Inc |
| 文件頁數(shù)： | 6/22頁 |
| 文件大小： | 0K |
| 描述： | IC ADC 12BIT DIFF IN 1MSPS 8MSOP |
| 標準包裝： | 50 |
| 位數(shù)： | 12 |
| 采樣率（每秒）： | 1M |
| 數(shù)據(jù)接口： | DSP，MICROWIRE?，QSPI?，串行，SPI? |
| 轉換器數(shù)目： | 1 |
| 功率耗散（最大）： | 9.25mW |
| 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： | 8-TSSOP，8-MSOP（0.118"，3.00mm 寬） |
| 供應商設備封裝： | 8-MSOP |
| 包裝： | 管件 |
| 輸入數(shù)目和類型： | 1 個差分，單極 |
| 配用： | EVAL-AD7450CBZ-ND - BOARD EVALUATION FOR AD7450 |
–14–
AD7450
The circuit configuration shown in Figure 15b converts a unipolar,
single-ended signal into a differential signal.
V+
V–
V+
V–
2
VREF p-p
VREF
27
390
220
10k
EXTERNAL
VREF
220
VDD
VIN+
VIN–
AD7450
220
0.1 F
A
VREF
GND
Figure 15b. Dual Op Amp Circuit to Convert a
Single-Ended Unipolar Input into a Differential Input
RF Transformer
In systems that do not need to be dc-coupled, an RF transformer
with a center tap offers a good solution for generating differential
inputs. Figure 16 shows how a transformer is used for single-
ended-to-differential conversion. It provides the benefits of
operating the ADC in the differential mode without contributing
additional noise and distortion. An RF transformer also has the
benefit of providing electrical isolation between the signal source
and the ADC. A transformer can be used for most ac applications.
The center tap is used to shift the differential signal to the
common-mode level required. In this case, it is connected to the
reference so the common-mode level is the value of the reference.
C
EXTERNAL
VREF (2.5V)
R
VREF
VIN+
AD7450
VIN–
2.5V
3.75V
1.25V
2.5V
3.75V
1.25V
Figure 16. Using an RF Transformer to Generate
Differential Inputs
REFERENCES SECTION
An external reference source is required to supply the reference to the
AD7450. This reference input can range from 100 mV to 3.5 V. With
a 5 V power supply, the specified reference is 2.5 V and the maximum
reference is 3.5 V. With a 3.3 V power supply, the specified refer-
ence is 1.25 V and the maximum reference is 2.4 V. In both cases,
the reference is functional from 100 mV. It is important to ensure
that, when choosing the reference value for a particular application,
the maximum analog input range (VIN max) is never greater than
VDD + 0.3 V to comply with the maximum ratings of the part. The
following two examples calculate the maximum VREF input that can be
used when operating the AD7450 at VDD of 5 V and 3.3 V, respectively.
Example 1:
VV
IN
DD
max
.
=+ 03
VV
V
IN
REF
max
=+
2
If V
V
DD
= 5
ThenV
V
IN max
.
= 53
Therefore
V
REF
32
5 3
×= .
VV
REF max
.
= 35
Therefore, when operating at VDD = 5 V, the value of VREF can
range from 100 mV to a maximum value of 3.5 V. When VDD =
4.75 V, VREF max = 3.37 V.
Example 2:
VV
IN
DD
max
.
=+ 03
VV
V
IN
REF
max
=+
2
If V
V
DD
= 33
.
ThenV
V
IN max
.
= 36
Therefore
V
REF
32
3 6
×= .
VV
REF max
.
= 24
Therefore, when operating at VDD = 3.3 V, the value of VREF
can range from 100 mV to a maximum value of 2.4 V. When
VDD = 2.7 V, VREF max = 2 V.
These examples show that the maximum reference applied to
the AD7450 is directly dependant on the value of VDD.
The performance of the part at different reference values is shown
in TPC 8 to TPC 12 and in TPC 15. The value of the reference
sets the analog input span and the common-mode voltage range.
Errors in the reference source will result in gain errors in the
AD7450 transfer function and will add to specified full-scale errors
on the part. A capacitor of 0.1
F should be used to decouple
the VREF pin to GND. Table I lists examples of suitable voltage
references to be used that are available from Analog Devices, and
Figure 17 shows a typical connection diagram for the VREF pin.
Table I. Examples of Suitable Voltage References
Output
Initial
Operating
Reference
Voltage
Accuracy (% Max)
Current ( A)
AD589
1.235
1.2–2.8
50
AD1580
1.225
0.08–0.8
50
REF192
2.5
0.08–0.4
45
REF43
2.5
0.06–0.1
600
AD780
2.5
0.04–0.2
1000
VREF
AD7450*
VDD
0.1 F
1
2
3
4
5
6
7
8
VIN
TEMP
GND
TRIM
VOUT
O/P SEL
NC
VDD
0.1 F
10nF
*ADDITIONAL PINS OMITTED FOR CLARITY
AD780
NC = NO CONNECT
2.5V
Figure 17. Typical VREF Connection Diagram for VDD = 5 V
Rev. A
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