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參數資料
| 型號： | AD7891BP-1 |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | ADC |
| 英文描述： | LC2MOS 8-Channel, 12-Bit High Speed Data Acquisition System |
| 中文描述： | 8-CH 12-BIT PROPRIETARY METHOD ADC, SERIAL/PARALLEL ACCESS, PQCC44 |
| 封裝： | PLASTIC, MO-047AC, LCC-44 |
| 文件頁數： | 14/20頁 |
| 文件大小： | 173K |
| 代理商： | AD7891BP-1 |
AD7891
–14–
REV. A
Track/Hold Amplifier section
The track/hold amplifier on the AD7891 allows the ADC to
accurately convert an input sine wave of full-scale amplitude to
12-bit accuracy. The input bandwidth of the track/hold is
greater than the Nyquist rate of the ADC even when the ADC is
operated at its maximum throughput rate of 454 kHz (AD7891-
1) or 500 kHz (AD7891-2). In other words, the track/hold
amplifier can handle input frequencies in excess of 227 kHz
(AD7891-1) or 250 kHz (AD7891-2).
The track/hold amplifier acquires an input signal in 600 ns
(AD7891-1) or 400 ns (AD7891-2). The operation of the track/
hold is essentially transparent to the user. The track/hold ampli-
fier goes from its tracking mode to its hold mode on the rising
edge of
CONVST
. The aperture time for the track/hold (i.e.,
the delay between the external
CONVST
signal and the track/
hold actually going into hold) is typically 15 ns. At the end of
conversion, the part returns to its tracking mode. The track/hold
starts acquiring the next signal at this point.
STANDBY
Operation
The AD7891 can be put into power save or standby mode by
use of the
STANDBY
pin or the SWSTBY bit of the control
register. Normal operation of the AD7891 takes place when the
STANDBY
input is at a logic one and the SWSTBY bit is at a
logic zero. When the
STANDBY
pin is brought low or a one is
written to the SWSTBY bit, then the part goes into its standby
mode of operation, which reduces its power consumption to
typically 75
μ
W.
The AD7891 is returned to normal operation when the
STANDBY
input is at a logic 1 and the SWSTBY bit is a logic
zero. The wake-up time of the AD7891 is normally determined
by the amount of time required to charge the 0.1
μ
F capacitor
between the REF OUT/REF IN pin and REFGND. If the inter-
nal reference is being used as the reference source, then this
capacitor is charged via a nominal 2 k
resistor. Assuming 10
time constants to charge the capacitor to 12-bit accuracy, this
implies a wake-up time of 2 ms.
If an external reference is used, then this will have to be taken
into account when working out how long it will take to charge
the capacitor. If the external reference has remained at 2.5 V
during the time the AD7891 was in standby mode, then the
capacitor will already be charged when the part is taken out of
standby mode. Thus the wake-up time is now the time required
for the internal circuitry of the AD7891 to settle to 12-bit accu-
racy. This typically takes 5
μ
s. If the external reference was also
put into standby then the wake-up time of the reference, com-
bined with the amount of time taken to recharge the reference
capacitor from the external reference, determines how much
time must elapse before conversions can begin again.
MICROPROCESSOR INTERFACING
AD7891 to 8X51 Serial Interface
A serial interface between the AD7891 and the 8X51 micro-
controller is shown in Figure 7. TXD of the 8X51 drives SCLK
of the AD7891 while RXD transmits data to and receives data
from the part. The serial clock speed of the 8X51 is slow com-
pared to the maximum serial clock speed of the AD7891, so
maximum throughput of the AD7891 is not achieved with this
interface.
8X51*
DATA OUT
AD7891*
*ADDITIONAL PINS OMITTED FOR CLARITY
SCLK
DATA IN
RFS
TFS
P3.4
P3.3
TXD
RXD
Figure 7. AD7891 to 8X51 Interface
The 8X51 provides the LSB of its SBUF register as the first bit
in the serial data stream. The AD7891 expects the MSB of the
6-bit write first. Therefore, the data in the SBUF register must
be arranged correctly so that this is taken into account. When
data is to be transmitted to the part, P3.3 is taken low. The
8XC51 transmits its data in 8-bit bytes with only 8 falling clock
edges occurring in the transmit cycle. One 8-bit transfer is
needed to write data to the control register of the AD7891.
After the data has been transferred, the P3.3 line is taken high
to complete the transmission.
When reading data from the AD7891, P3.4 of the 8X51 is taken
low. Two 8-bit serial reads are performed by the 8X51 and P3.4
is taken high to complete the transfer. Again, the 8X51 expects
the LSB first, while the AD7891 transmits MSB first, so this
must be taken into account in the 8X51 software.
No provision has been made in the given interface to determine
when a conversion has ended. If the conversions are initiated by
software, then the 8X51 can wait a predetermined amount of
time before reading back valid data. Alternately the falling edge
of the
EOC
signal can be used to initiate an interrupt service
routine which reads the conversion result from part to part.
AD7891 to 68HC11 Serial Interface
Figure 8 shows a serial interface between the AD7891 and the
68HC11 microcontroller. SCK of the 68HC11 drives SCLK of
the AD7891, the MOSI output drives DATA IN of the AD7891
and the MISO input receives data from DATA OUT of the
AD7891. Ports PC6 and PC7 of the 68HC11 drive the
TFS
and
RFS
lines of the AD7891 respectively.
For correct operation of this interface, the 68HC11 should be
configured such that its CPOL bit is a 1 and its CPHA bit is a 0.
When data is to be transferred to the AD7891, PC7 is taken
low. When data is to be received from the AD7891, PC6 is
taken low. The 68HC11 transmits and receives its serial data in
8-bit bytes, MSB first. The AD7891 transmits and receives data
MSB first also. Eight falling clock edges occur in a read or write
cycle from the 68HC11. A single 8-bit write with PC7 low is
required to write to the control register. When data has been
written, PC7 is taken high. When reading from the AD7891,
PC6 is left low after the first eight bits have been read. A second
byte of data is then transmitted serially from the AD7891. When
this transfer is complete, the PC6 line is taken high.
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相關代理商/技術參數 |
參數描述 |
|---|---|
| AD7891BP-1REEL | 功能描述:IC DAS 12BIT 8CH 44-PLCC RoHS:否 類別:集成電路 (IC) >> 數據采集 - ADCs/DAC - 專用型 系列:- 產品培訓模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:50 系列:- 類型:數據采集系統（DAS） 分辨率（位）:16 b 采樣率（每秒）:21.94k 數據接口:MICROWIRE?，QSPI?，串行，SPI? 電壓電源:模擬和數字 電源電壓:1.8 V ~ 3.6 V 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:40-WFQFN 裸露焊盤 供應商設備封裝:40-TQFN-EP（6x6） 包裝:托盤 |
| AD7891BP2 | 制造商:Analog Devices 功能描述: |
| AD7891BP-2 | 功能描述:IC DAS 12BIT 8CH 44-PLCC RoHS:否 類別:集成電路 (IC) >> 數據采集 - ADCs/DAC - 專用型 系列:- 產品培訓模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:50 系列:- 類型:數據采集系統（DAS） 分辨率（位）:16 b 采樣率（每秒）:21.94k 數據接口:MICROWIRE?，QSPI?，串行，SPI? 電壓電源:模擬和數字 電源電壓:1.8 V ~ 3.6 V 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:40-WFQFN 裸露焊盤 供應商設備封裝:40-TQFN-EP（6x6） 包裝:托盤 |
| AD7891BP-2REEL | 功能描述:IC DAS 12BIT 8CH 44-PLCC RoHS:否 類別:集成電路 (IC) >> 數據采集 - ADCs/DAC - 專用型 系列:- 產品培訓模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:50 系列:- 類型:數據采集系統（DAS） 分辨率（位）:16 b 采樣率（每秒）:21.94k 數據接口:MICROWIRE?，QSPI?，串行，SPI? 電壓電源:模擬和數字 電源電壓:1.8 V ~ 3.6 V 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:40-WFQFN 裸露焊盤 供應商設備封裝:40-TQFN-EP（6x6） 包裝:托盤 |
| AD7891BPZ-1 | 功能描述:IC DAS 12BIT 8CH 44-PLCC RoHS:是 類別:集成電路 (IC) >> 數據采集 - ADCs/DAC - 專用型 系列:- 產品培訓模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:50 系列:- 類型:數據采集系統（DAS） 分辨率（位）:16 b 采樣率（每秒）:21.94k 數據接口:MICROWIRE?，QSPI?，串行，SPI? 電壓電源:模擬和數字 電源電壓:1.8 V ~ 3.6 V 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:40-WFQFN 裸露焊盤 供應商設備封裝:40-TQFN-EP（6x6） 包裝:托盤 |
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