參數(shù)資料
型號: EVAL-AD7690SDZ
廠商: Analog Devices Inc
文件頁數(shù): 4/24頁
文件大?。?/td> 0K
描述: BOARD EVAL FOR AD7690
標準包裝: 1
系列: PulSAR®
ADC 的數(shù)量: 1
位數(shù): 18
采樣率(每秒): 400k
數(shù)據(jù)接口: DSP,MICROWIRE?,QSPI?,串行,SPI?
輸入范圍: ±VREF
在以下條件下的電源(標準): 17mW @ 100kSPS
工作溫度: -40°C ~ 85°C
已用 IC / 零件: AD7690
已供物品:
AD7690
Rev. B | Page 12 of 24
THEORY OF OPERATION
SW+
MSB
65,536C
IN+
LSB
COMP
CONTROL
LOGIC
SWITCHES CONTROL
BUSY
OUTPUT CODE
CNV
REF
GND
IN–
4C
2C
C
131,072C
SW–
MSB
65,536C
LSB
4C
2C
C
131,072C
0
57
92
-00
6
Figure 24. ADC Simplified Schematic
CIRCUIT INFORMATION
The AD7690 is a fast, low power, single-supply, precise, 18-bit
ADC using a successive approximation architecture.
The AD7690 is capable of converting 400,000 samples per
second (400 kSPS) and powers down between conversions.
When operating at 1 kSPS, for example, it consumes 50 μW
typically, ideal for battery-powered applications.
The AD7690 provides the user with an on-chip track-and-hold
and does not exhibit pipeline delay or latency, making it ideal
for multiple multiplexed channel applications.
The AD7690 is specified from 4.75 V to 5.25 V and can be
interfaced to any 1.8 V to 5 V digital logic family. It is housed in
a 10-lead MSOP or a tiny 10-lead QFN (LFCSP) that allows
space savings and flexible configurations.
It is pin-for-pin compatible with the 18-bit AD7691 and AD7982
and the 16-bit AD7687, AD7688, and AD7693.
CONVERTER OPERATION
The AD7690 is a successive approximation ADC based on a
charge redistribution DAC. Figure 24 shows the simplified
schematic of the ADC. The capacitive DAC consists of two
identical arrays of 18 binary-weighted capacitors, which are
connected to the two comparator inputs.
During the acquisition phase, terminals of the array tied to the
comparator’s input are connected to GND via SW+ and SW.
All independent switches are connected to the analog inputs.
Thus, the capacitor arrays are used as sampling capacitors and
acquire the analog signal on the IN+ and IN inputs. When the
acquisition phase is complete and the CNV input goes high, a
conversion phase is initiated. When the conversion phase
begins, SW+ and SW are opened first. The two capacitor
arrays are then disconnected from the inputs and connected to
the GND input. Therefore, the differential voltage between the
IN+ and IN inputs captured at the end of the acquisition phase
is applied to the comparator inputs, causing the comparator to
become unbalanced. By switching each element of the capacitor
array between GND and REF, the comparator input varies by
binary-weighted voltage steps (VREF/2, VREF/4 ... VREF/262,144).
The control logic toggles these switches, starting with the MSB,
to bring the comparator back into a balanced condition. After
the completion of this process, the part returns to the
acquisition phase, and the control logic generates the ADC
output code and a busy signal indicator.
Because the AD7690 has an on-board conversion clock, the
serial clock, SCK, is not required for the conversion process.
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