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參數(shù)資料
| 型號： | AD7707BR |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | ADC |
| 英文描述： | 3 V/5 V, +-10 V Input Range, 1 mW 3-Channel 16-Bit, Sigma-Delta ADC |
| 中文描述： | 3-CH 16-BIT DELTA-SIGMA ADC, SERIAL ACCESS, PDSO20 |
| 封裝： | 0.300 INCH, SOIC-20 |
| 文件頁數(shù)： | 27/40頁 |
| 文件大?。?/td> | 316K |
| 代理商： | AD7707BR |
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REV. A
AD7707
–27–
Supply Current
The current consumption on the AD7707 is specified for sup-
plies in the range +2.7 V to +3.3 V and in the range +4.75 V to
+5.25 V. The part operates over a +2.7 V to +5.25 V supply
range and the I
DD
for the part varies as the supply voltage varies
over this range. There is an internal current boost bit on the
AD7707 that is set internally in accordance with the operating
conditions. This affects the current drawn by the analog cir-
cuitry within these devices. Minimum power consumption is
achieved when the AD7707 is operated with an f
CLKIN
of 1 MHz
or at gains of 1 to 4 with f
CLKIN
= 2.4575 MHz as the internal
boost bit is off reducing the analog current consumption. Figure
17 shows the variation of the typical I
DD
with V
DD
voltage for
both a 1MHz crystal oscillator and a 2.4576 MHz crystal oscil-
lator at +25
°
C. The AD7707 is operated in unbuffered mode.
The relationship shows that the I
DD
is minimized by operating
the part with lower V
DD
voltages. I
DD
on the AD7707 is also
minimized by using an external master clock or by optimizing
external components when using the on-chip oscillator circuit.
Figures 3, 4, 6 and 7 show variations in I
DD
with gain, V
DD
and
clock frequency using an external clock.
Grounding and Layout
Since the analog inputs and reference input are differential,
most of the voltages in the analog modulator are common-mode
voltages. The excellent common-mode rejection of the part will
remove common-mode noise on these inputs. The digital filter
will provide rejection of broadband noise on the power supplies,
except at integer multiples of the modulator sampling frequency.
The digital filter also removes noise from the analog and refer-
ence inputs provided those noise sources do not saturate the
analog modulator. As a result, the AD7707 is more immune to
noise interference than a conventional high resolution converter.
However, because the resolution of the AD7707 is so high, and
the noise levels from the AD7707 so low, care must be taken
with regard to grounding and layout.
The printed circuit board that houses the AD7707 should be
designed so that the analog and digital sections are separated
and confined to certain areas of the board. This facilitates the
use of ground planes which can be separated easily. A minimum
etch technique is generally best for ground planes as it gives the
best shielding. Digital and analog ground planes should only be
joined in one place to avoid ground loops. If the AD7707 is in a
system where multiple devices require AGND-to-DGND con-
nections, the connection should be made at one point only, a
star ground point which should be established as close as pos-
sible to the AD7707.
Avoid running digital lines under the device as these might
couple noise onto the analog circuitry within the AD7707. The
analog ground plane should be allowed to run under the AD7707
to reduce noise coupling. The power supply lines to the AD7707
should use wide traces to provide low impedance paths and
reduce the effects of glitches on the power supply line. Fast
switching signals like clocks should be shielded with digital
ground to avoid radiating noise to other sections of the board
and clock signals should never be run near the analog inputs.
Avoid crossover of digital and analog signals. Traces on opposite
sides of the board should run at right angles to each other. This
will reduce the effects of feedthrough through the board. A
microstrip technique is by far the best, but is not always possible
with a double-sided board. In this technique, the component
side of the board is dedicated to ground planes while signals are
placed on the solder side.
Good decoupling is important when using high resolution ADCs.
All analog supplies should be decoupled with 10
μ
F tantalum in
parallel with 0.1
μ
F ceramic capacitors to GND. To achieve the
best from these decoupling components, they have to be placed
as close as possible to the device, ideally right up against the
device. All logic chips should be decoupled with 0.1
μ
F disc
ceramic capacitors to DGND.
Evaluating the AD7707 Performance
The recommended layout for the AD7707 is outlined in the
evaluation board. The evaluation board package include a fully
assembled and tested evaluation board, documentation, soft-
ware for controlling the board over the printer port of a PC and
software for analyzing their performance on the PC.
Noise levels in the signals applied to the AD7707 may also
affect performance of the part. The AD7707 software evaluation
package allows the user to evaluate the true performance of the
part, independent of the analog input signal. The scheme in-
volves using a test mode on the part where the inputs to the
AD7707 are internally shorted together to provide a zero differ-
ential voltage for the analog modulator. External to the device,
the LOCOM and HICOM inputs on the AD7707 should be
connected to voltages that are within the allowable common-
mode range of the part. This scheme should be used after a
calibration has been performed on the part.
DIGITAL INTERFACE
As previously outlined, the AD7707’s programmable functions
are controlled using a set of on-chip registers. Data is written to
these registers via the part’s serial interface and read access to
the on-chip registers is also provided by this interface. All com-
munications to the part must start with a write operation to the
Communications Register. After power-on or
RESET
, the de-
vice expects a write to its Communications Register. The data
written to this register determines whether the next operation to
the part is a read or a write operation and also determines to
which register this read or write operation occurs. Therefore,
write access to any of the other registers on the part starts with a
write operation to the Communications Register followed by a
write to the selected register. A read operation from any other
register on the part (including the output data register) starts
with a write operation to the Communications Register followed
by a read operation from the selected register.
The AD7707’s serial interface consists of five signals,
CS
,
SCLK, DIN, DOUT and
DRDY
. The DIN line is used for
transferring data into the on-chip registers while the DOUT line
is used for accessing data from the on-chip registers. SCLK is
the serial clock input for the device and all data transfers (either
on DIN or DOUT) take place with respect to this SCLK signal.
The
DRDY
line is used as a status signal to indicate when data
is ready to be read from the AD7707’s data register.
DRDY
goes low when a new data word is available in the output regis-
ter. It is reset high when a read operation from the data register
is complete. It also goes high prior to the updating of the output
register to indicate when
not
to read from the device to ensure
that a data read is not attempted while the register is being
updated.
CS
is used to select the device. It can be used to de-
code the AD7707 in systems where a number of parts are con-
nected to the serial bus.
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| AD7707BR-REEL | 制造商:Analog Devices 功能描述:ADC Single Delta-Sigma 500sps 16-bit Serial 20-Pin SOIC W T/R 制造商:Analog Devices 功能描述:ADC SGL DELTA-SIGMA 0.5KSPS 16BIT SERL 20SOIC W - Tape and Reel |
| AD7707BR-REEL7 | 制造商:Analog Devices 功能描述:ADC Single Delta-Sigma 500sps 16-bit Serial 20-Pin SOIC W T/R 制造商:Analog Devices 功能描述:ADC SGL DELTA-SIGMA 0.5KSPS 16BIT SERL 20SOIC W - Tape and Reel |
| AD7707BRU | 功能描述:IC ADC 16BIT 3CH 20-TSSOP RoHS:否 類別:集成電路 (IC) >> 數(shù)據(jù)采集 - 模數(shù)轉(zhuǎn)換器 系列:- 標(biāo)準(zhǔn)包裝:1,000 系列:- 位數(shù):12 采樣率（每秒）:300k 數(shù)據(jù)接口:并聯(lián) 轉(zhuǎn)換器數(shù)目:1 功率耗散（最大）:75mW 電壓電源:單電源 工作溫度:0°C ~ 70°C 安裝類型:表面貼裝 封裝/外殼:24-SOIC（0.295"，7.50mm 寬） 供應(yīng)商設(shè)備封裝:24-SOIC 包裝:帶卷 (TR) 輸入數(shù)目和類型:1 個單端，單極；1 個單端，雙極 |
| AD7707BRU-REEL | 制造商:Analog Devices 功能描述:ADC Single Delta-Sigma 500sps 16-bit Serial 20-Pin TSSOP T/R 制造商:Analog Devices 功能描述:ADC SGL DELTA-SIGMA 0.5KSPS 16BIT SERL 20TSSOP - Tape and Reel |
| AD7707BRU-REEL7 | 功能描述:IC ADC 16BIT 3CH 20-TSSOP T/R RoHS:否 類別:集成電路 (IC) >> 數(shù)據(jù)采集 - 模數(shù)轉(zhuǎn)換器 系列:- 標(biāo)準(zhǔn)包裝:1,000 系列:- 位數(shù):16 采樣率（每秒）:45k 數(shù)據(jù)接口:串行 轉(zhuǎn)換器數(shù)目:2 功率耗散（最大）:315mW 電壓電源:模擬和數(shù)字 工作溫度:0°C ~ 70°C 安裝類型:表面貼裝 封裝/外殼:28-SOIC（0.295"，7.50mm 寬） 供應(yīng)商設(shè)備封裝:28-SOIC W 包裝:帶卷 (TR) 輸入數(shù)目和類型:2 個單端，單極 |
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