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| 型号： | AD7730BRU-REEL7 |
| 厂商： | Analog Devices Inc |
| 文件页数： | 36/53页 |
| 文件大小： | 0K |
| 描述： | IC ADC TRANSDUCER BRIDGE 24TSSOP |
| 标准包装： | 1,000 |
| 位数： | 24 |
| 通道数： | 1 |
| 功率（瓦特）： | 125mW |
| 电压 - 电源，模拟： | 4.75 V ~ 5.25 V |
| 电压 - 电源，数字： | 2.7 V ~ 5.25 V |
| 封装/外壳： | 24-TSSOP（0.173"，4.40mm 宽） |
| 供应商设备封装： | 24-TSSOP |
| 包装： | 带卷 (TR) |
| 配用： | EVAL-AD7730LEBZ-ND - BOARD EVALUATION FOR AD7730 EVAL-AD7730EBZ-ND - BOARD EVAL FOR AD7730 |
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AD7730/AD7730L
–41–
Long lead lengths from the bridge to the AD7730 facilitate the
pickup of mains frequency on the analog input, the reference
input and the power supply. The analog inputs to the AD7730
are buffered, which allows the user to connect whatever noise
reduction capacitors are necessary in the application. The AD7730
boasts excellent common-mode and normal- mode rejection of
mains frequency on both the analog and reference inputs. In
CHOP mode, care must be taken in choosing the output update
rate so it does not result in reducing line frequency rejection
(see DIGITAL FILTERING section). The input offset current
on the AD7730 is 10 nA maximum which results in a maxi-
mum, dc offset voltage of 1.75 mV in a 350
Ω bridge applica-
tion. Care should taken with inserting large source impedances
on the reference input pins as these inputs are not buffered and
the source impedances can result in gain errors.
In many load-cell applications, a portion of the dynamic range
of the bridge output is consumed by a pan weight or tare weight.
In such applications, the 6-bit TARE DAC of the AD7730 can
be used to adjust out this tare weight as outlined previously.
AC Excitation of Bridge
AC excitation of the bridge addresses many of the concerns with
thermocouple, offset and drift effects encountered in dc-excited
applications. In ac-excitation, the polarity of the excitation volt-
age to the bridge is reversed on alternate cycles. The result is the
elimination of dc errors at the expense of a more complex sys-
tem design. Figure 24 outlines the connections for an ac-excited
bridge application based on the AD7730.
The excitation voltage to the bridge must be switched on
alternate cycles. Transistors T1 to T4 in Figure 24 perform
the switching of the excitation voltage. These transistors can be
discrete matched bipolar or MOS transistors, or a dedicated
bridge driver chip such as the 4427 from Micrel can be used to
perform the task.
Since the analog input voltage and the reference voltage are
reversed on alternate cycles, the AD7730 must be synchronized
with this reversing of the excitation voltage. To allow the
AD7730 to synchronize itself with this switching, it provides the
logic control signals for the switching of the excitation voltage.
These signals are the nonoverlapping CMOS outputs ACX
and
ACX.
One of the problems encountered with ac-excitation is the set-
tling time associated with the analog input signals after the
excitation voltage is switched. This is particularly true in appli-
cations where there are long lead lengths from the bridge to the
AD7730. It means that the converter could encounter errors
because it is processing signals which are not fully settled. The
AD7730 addresses this problem by allowing the user to program
a delay of up to 48.75
μs between the switching of the ACX
signals and the processing of data at the analog inputs. This is
achieved using the DL bits of the Filter Register.
The AD7730 also scales the ACX switching frequency in accor-
dance with the output update rate. This avoids situations where
the bridge is switched at an unnecessarily faster rate than the
system requires.
The fact that the AD7730 can handle reference voltages which
are the same as the excitation voltages is particularly useful in
ac-excitation where resistor divider arrangements on the
reference input add to the settling time associated with the
switching.
Figure 24. Typical Connections for AC-Excited Bridge Application
SIGMA-
DELTA
MODULATOR
AVDD
DVDD
AD7730
6-BIT
DAC
SERIAL INTERFACE
AND CONTROL LOGIC
REGISTER BANK
CLOCK
GENERATION
PROGRAMMABLE
DIGITAL
FILTER
SIGMA-DELTA A/D CONVERTER
BUFFER
PGA
AIN2(+)/D1
AIN2(–)/D0
ACX
STANDBY
SYNC
MCLK IN
MCLK OUT
SCLK
CS
DIN
DOUT
RESET
RDY
POL
DGND
AGND
MUX
AC
EXCITATION
CLOCK
CALIBRATION
MICROCONTROLLER
+
IN+
OUT–
IN–
OUT+
REF IN(+)
REF IN(–)
AIN1(+)
AIN1(–)
EXCITATION VOLTAGE = +5V
T4
T3
T2
T1
+/–
REV. B
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| AD7730BRUZ | 功能描述:IC ADC TRANSDUCER BRIDGE 24TSSOP RoHS:是 类别:集成电路 (IC) >> 数据采集 - 模拟前端 (AFE) 系列:- 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:2,500 系列:- 位数:- 通道数:2 功率（瓦特）:- 电压 - 电源，模拟:3 V ~ 3.6 V 电压 - 电源，数字:3 V ~ 3.6 V 封装/外壳:32-VFQFN 裸露焊盘 供应商设备封装:32-QFN（5x5） 包装:带卷 (TR) |
| AD7730BRUZ-REEL | 功能描述:IC ADC BRIDGE TRANSDUCER 24TSSOP RoHS:是 类别:集成电路 (IC) >> 数据采集 - 模拟前端 (AFE) 系列:- 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:2,500 系列:- 位数:- 通道数:2 功率（瓦特）:- 电压 - 电源，模拟:3 V ~ 3.6 V 电压 - 电源，数字:3 V ~ 3.6 V 封装/外壳:32-VFQFN 裸露焊盘 供应商设备封装:32-QFN（5x5） 包装:带卷 (TR) |
| AD7730BRUZ-REEL7 | 功能描述:IC ADC BRIDGE TRANSDUCER 24TSSOP RoHS:是 类别:集成电路 (IC) >> 数据采集 - 模拟前端 (AFE) 系列:- 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:2,500 系列:- 位数:- 通道数:2 功率（瓦特）:- 电压 - 电源，模拟:3 V ~ 3.6 V 电压 - 电源，数字:3 V ~ 3.6 V 封装/外壳:32-VFQFN 裸露焊盘 供应商设备封装:32-QFN（5x5） 包装:带卷 (TR) |
| AD7730BRZ | 功能描述:IC ADC BRIDGE TRANSDUCER 24-SOIC RoHS:是 类别:集成电路 (IC) >> 数据采集 - 模拟前端 (AFE) 系列:- 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:2,500 系列:- 位数:- 通道数:2 功率（瓦特）:- 电压 - 电源，模拟:3 V ~ 3.6 V 电压 - 电源，数字:3 V ~ 3.6 V 封装/外壳:32-VFQFN 裸露焊盘 供应商设备封装:32-QFN（5x5） 包装:带卷 (TR) |
| AD7730BRZ | 制造商:Analog Devices 功能描述:IC, ADC, 24BIT, 1.2KSPS, SOIC-24 |
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