參數(shù)資料
型號(hào)： AD7927BRUZ-REEL
廠商： Analog Devices Inc
文件頁(yè)數(shù)： 14/28頁(yè)
文件大?。?/td> 0K
描述： IC ADC 12BIT 8CH W/SEQ 20TSSOP
標(biāo)準(zhǔn)包裝： 2,500
位數(shù)： 12
采樣率（每秒）： 200k
數(shù)據(jù)接口： DSP，MICROWIRE?，QSPI?，串行，SPI?
轉(zhuǎn)換器數(shù)目： 1
功率耗散（最大）： 7.5mW
電壓電源： 單電源
工作溫度： -40°C ~ 85°C
安裝類型： 表面貼裝
封裝/外殼： 20-TSSOP（0.173"，4.40mm 寬）
供應(yīng)商設(shè)備封裝： 20-TSSOP
包裝： 帶卷 (TR)
輸入數(shù)目和類型： 8 個(gè)單端，單極
配用： EVAL-AD7927CBZ-ND - BOARD EVALUATION FOR AD7927
Data Sheet
AD7927
Rev. D | Page 21 of 28
1
SCLK
DOUT
DIN
16
1
16
DUMMY CONVERSION
INVALID DATA
KEEP DIN LINE TIED HIGH FOR FIRST TWO DUMMY CONVERSIONS
12
DUMMY CONVERSION
INVALID DATA
16
CORRECT VALUE IN CONTROL REGISTER,
VALID DATA FROM NEXT CONVERSION,
USER CAN WRITE TO SHADOW REGISTER
IN NEXT CONVERSION
CONTROL REGISTER IS LOADED ON THE FIRST
12 CLOCK EDGES
DATA INTO CONTROL REGISTER
CS
03
08
8-
0
24
Figure 24. Three-Dummy-Conversions to Place AD7927 into the Required Operating Mode After Power Supplies Are Applied
POWERING UP THE AD7927
When supplies are first applied to the AD7927, the ADC may
power up in any of the operating modes of the part. To ensure
that the part is placed into the required operating mode, the
user should perform a dummy cycle operation as outlined in
The three-dummy-conversion operation outlined in Figure 24
must be performed to place the part into the auto shutdown
mode. The first two conversions of this dummy cycle operation
are performed with the DIN line tied high, and for the third
conversion of the dummy cycle operation, the user should
write the desired control register configuration to the AD7927
to place the part into the auto shutdown mode. On the third CS
rising edge after the supplies are applied, the control register
contains the correct information and valid data results from the
next conversion.
Therefore, to ensure the part is placed into the correct operating
mode, when supplies are first applied to the AD7927, the user
must first issue two serial write operations with the DIN line
tied high, and on the third conversion cycle the user can then
write to the control register to place to part into any of the oper-
ating modes. The user should not write to the shadow register
until the fourth conversion cycle after the supplies are applied
to the ADC, to guarantee the control register contains the
correct data.
If the user wishes to place the part into either the normal or full
shutdown mode, the second dummy cycle with DIN tied high
can be omitted from the three-dummy-conversion operation
outlined in Figure 24.
POWER VS. THROUGHPUT RATE
In auto shutdown mode, the average power consumption of
the ADC may be reduced at any given throughput rate. The
power saving depends on the SCLK frequency used, that is,
conversion time. In some cases where the conversion time is
quite a proportion of the cycle time, the throughput rate needs
to be reduced to take advantage of the power-down modes.
Assuming a 20 MHz SCLK is used, the conversion time is
800 ns, but the cycle time is 5 μs when the sampling rate is at a
maximum of 200 kSPS. If the AD7927 is placed into shutdown
for the remainder of the cycle time, then on average far less power
is consumed in every cycle compared to leaving the device in
normal mode. Furthermore, Figure 25 shows how as the through-
put rate is reduced, the part remains in its shutdown longer and
the average power consumption drops accordingly over time.
For example, if the AD7927 is operated in a continuous sampling
mode, with a throughput rate of 200 kSPS and an SCLK of 20 MHz
(AVDD = 5 V), and the device is placed in auto shutdown mode,
that is, if PM1 = 0 and PM0 = 1, then the power consumption is
calculated as follows.
The maximum power dissipation during the conversion time is
13.5 mW (IDD = 2.7 mA maximum, AVDD = 5 V). If the power-
up time from auto shutdown is 1 μs and the remaining conversion
time is another cycle, that is, 800 ns, the AD7927 can be said to
dissipate 13.5 mW for 1.8 μs during each conversion cycle. For
the remainder of the conversion cycle, 3.2 μs, the part remains
in shutdown. The AD7927 can be said to dissipate 2.5 μW for
the remaining 3.2 μs of the conversion cycle. If the throughput
rate is 200 kSPS, the cycle time is 5 μs and the average power
dissipated during each cycle is (1.8/5) × (13.5 mW) + (3.2/5) ×
(2.5 μW) = 4.8616 mW.
Figure 25 shows the maximum power vs. throughput rate when
using the auto shutdown mode with 3 V and 5 V supplies.
THROUGHPUT (kSPS)
10
0
200
P
O
WE
R
(
m
W)
0.1
0.01
80
1
100
140
180
20
40
60
120
160
AVDD = 5V
AVDD = 3V
03
08
8-
0
25
Figure 25. Power vs. Throughput Rate
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AD7927BRUZ-REEL7 功能描述:IC ADC 12BIT 8CH W/SEQ 20TSSOP RoHS:是 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:2,500 系列:- 位數(shù):16 采樣率（每秒）:15 數(shù)據(jù)接口:MICROWIRE?，串行，SPI? 轉(zhuǎn)換器數(shù)目:1 功率耗散（最大）:480µW 電壓電源:單電源 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:38-WFQFN 裸露焊盤 供應(yīng)商設(shè)備封裝:38-QFN（5x7） 包裝:帶卷 (TR) 輸入數(shù)目和類型:16 個(gè)單端，雙極；8 個(gè)差分，雙極 配用:DC1011A-C-ND - BOARD DELTA SIGMA ADC LTC2494
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