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参数资料
| 型号： | EVAL-AD7687SDZ |
| 厂商： | Analog Devices Inc |
| 文件页数： | 9/28页 |
| 文件大小： | 0K |
| 描述： | BOARD EVAL FOR AD7687 |
| 标准包装： | 1 |
| 系列： | PulSAR® |
| ADC 的数量： | 1 |
| 位数： | 16 |
| 采样率（每秒）： | 250k |
| 数据接口： | 串行 |
| 输入范围： | ±VREF |
| 在以下条件下的电源（标准）： | 4mW @ 5V，100kSPS |
| 工作温度： | -40°C ~ 85°C |
| 已用 IC / 零件： | AD7687 |
| 已供物品： | 板 |
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Data Sheet
AD7687
Rev. B | Page 17 of 28
insensitive to power supply variations over a wide frequency
range, as shown in Figure 32, which represents PSRR over
frequency.
FREQUENCY (kHz)
PSRR
(dB)
100
95
90
85
80
75
70
65
60
55
50
1
10
100
1000
10000
02972-
031
VDD = 5V
VDD = 2.5V
Figure 32. PSRR vs. Frequency
The AD7687 powers down automatically at the end of each
conversion phase and, therefore, the power scales linearly with
the sampling rate, as shown in Figure 33. This makes the part
ideal for low sampling rate (even a few Hz) and low battery-
powered applications.
SAMPLING RATE (SPS)
OPERATI
NG
CURRENT
(
μA)
1000
10
0.1
0.001
10
100
1000
10000
100000
1000000
02972-
032
VIO
VDD = 5V
VDD = 2.5V
Figure 33. Operating Currents vs. Sampling Rate
SUPPLYING THE ADC FROM THE REFERENCE
For simplified applications, the AD7687, with its low operating
current, can be supplied directly using the reference circuit
shown in Figure 34. The reference line can be driven by either:
The system power supply directly
A reference voltage with enough current output capability,
such as the ADR43x
A reference buffer, such as the AD8031, which can also
filter the system power supply, as shown in Figure 34
AD8031
AD7687
VIO
REF
VDD
10
μF
1
μF
10
Ω
10k
Ω
5V
1
μF
1
02972-
033
1OPTIONAL REFERENCE BUFFER AND FILTER.
Figure 34. Example of Application Circuit
DIGITAL INTERFACE
Though the AD7687 has a reduced number of pins, it offers
flexibility in its serial interface modes.
The AD7687, when in CS mode, is compatible with SPI, QSPI,
digital hosts, and DSPs, for example, Blackfin ADSP-BF53x or
ADSP-219x. This interface can use either 3-wire or 4-wire. A 3-
wire interface using the CNV, SCK, and SDO signals minimizes
wiring connections useful, for instance, in isolated applications.
A 4-wire interface using the SDI, CNV, SCK, and SDO signals
allows CNV, which initiates the conversions, to be independent
of the readback timing (SDI). This is useful in low jitter
sampling or simultaneous sampling applications.
The AD7687, when in chain mode, provides a daisy chain
feature using the SDI input for cascading multiple ADCs on a
single data line similar to a shift register.
The mode in which the part operates depends on the SDI level
when the CNV rising edge occurs. The CS mode is selected if
SDI is high and the chain mode is selected if SDI is low. The
SDI hold time is such that when SDI and CNV are connected
together, the chain mode is always selected.
In either mode, the AD7687 offers the flexibility to optionally
force a start bit in front of the data bits. This start bit can be
used as a BUSY signal indicator to interrupt the digital host and
trigger the data reading. Otherwise, without a BUSY indicator,
the user must time out the maximum conversion time prior to
readback.
The BUSY indicator feature is enabled as:
In the CS mode, if CNV or SDI is low when the ADC
conversion ends (
and
).
In the chain mode, if SCK is high during the CNV rising edge
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