參數(shù)資料
型號: AD9244BSTZRL-65
廠商: Analog Devices Inc
文件頁數(shù): 14/36頁
文件大小: 0K
描述: IC ADC 14BIT SGL 65MSPS 48LQFP
標(biāo)準(zhǔn)包裝: 2,000
位數(shù): 14
采樣率(每秒): 65M
數(shù)據(jù)接口: 并聯(lián)
轉(zhuǎn)換器數(shù)目: 1
功率耗散(最大): 550mW
電壓電源: 模擬和數(shù)字
工作溫度: -40°C ~ 85°C
安裝類型: 表面貼裝
封裝/外殼: 48-LQFP
供應(yīng)商設(shè)備封裝: 48-LQFP(7x7)
包裝: 帶卷 (TR)
輸入數(shù)目和類型: 2 個單端,單極;1 個差分,單極
AD9244
Rev. C | Page 21 of 36
Using an External Reference
To use an external reference, the internal reference must be dis-
abled by connecting the SENSE pin to AVDD. The AD9244
contains an internal reference buffer, A2 (see Figure 48), that
simplifies the drive requirements of an external reference. The
external reference must be able to drive a 5 kΩ (±20%) load.
The bandwidth of the reference is deliberately left small to
minimize the reference noise contribution. As a result, it is not
possible to drive VREF externally with high frequencies.
Figure 51 shows an example of an external reference driving
both VIN– and VREF. In this case, both the common-mode
voltage and input span are directly dependent on the value of
VREF. Both the input span and the center of the input span are
equal to the external VREF. Thus, the valid input range extends
from (VREF + VREF/2) to (VREF VREF/2). For example, if
the Precision Reference Part REF191, a 2.048 V external refer-
ence, is used, the input span is 2.048 V. In this case, 1 LSB of the
AD9244 corresponds to 0.125 mV.
It is essential that a minimum of a 10 μF capacitor, in parallel
with a 0.1 μF low inductance ceramic capacitor, decouple the
reference output to AGND.
5V
AVDD
REFT
REFB
VREF
SENSE
AD9244
VIN+
VIN–
33
Ω
20pF
0.1
μF
0.1
μF
0.1
μF
0.1
μF
0.1
μF
10
μF
10
μF
33
Ω
+
VREF + VREF/2
VREF – VREF/2
VREF
02
40
4-
05
1
Figure 51. Using an External Reference
Digital Outputs
Table 10 details the relationship among the ADC input, OTR,
and digital output format.
Data Format Select (DFS)
The AD9244 can be programmed for straight binary or twos
complement data on the digital outputs. Connect the DFS pin to
AGND for straight binary and to AVDD for twos complement.
Digital Output Driver Considerations
The AD9244 output drivers can be configured to interface with
5 V or 3.3 V logic families by setting DRVDD to 5 V or 3.3 V,
respectively. The output drivers are sized to provide sufficient
output current to drive a wide variety of logic families.
However, large drive currents tend to cause glitches on the
supplies and can affect converter performance. Applications
requiring the ADC to drive large capacitive loads or large
fanouts can require external buffers or latches.
DIGITAL INPUTS AND OUTPUTS
Table 10. Output Data Format
Input (V)
Condition (V)
Binary Output Mode
Twos Complement Mode
OTR
VIN+ – VIN
< –VREF/2 0.5 LSB
00 0000 0000 0000
10 0000 0000 0000
1
VIN+ – VIN
= VREF/2
00 0000 0000 0000
10 0000 0000 0000
0
VIN+ – VIN
= 0
10 0000 0000 0000
00 0000 0000 0000
0
VIN+ – VIN
= +VREF/2 1.0 LSB
11 1111 1111 1111
01 1111 1111 1111
0
VIN+ – VIN
> +VREF/2 0.5 LSB
11 1111 1111 1111
01 1111 1111 1111
1
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