VDD PD CONVST tPOWE" />
參數資料
型號: AD7822BRU-REEL
廠商: Analog Devices Inc
文件頁數: 7/28頁
文件大?。?/td> 0K
描述: IC ADC 8BIT 1CH 2MSPS 20TSSOP
標準包裝: 2,500
位數: 8
采樣率(每秒): 2M
數據接口: 并聯(lián)
轉換器數目: 1
功率耗散(最大): 36mW
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)
供應商設備封裝: 20-TSSOP
包裝: 帶卷 (TR)
輸入數目和類型: 1 個單端,單極
AD7822/AD7825/AD7829
Rev. C | Page 15 of 28
VDD
PD
CONVST
tPOWER-UP
1s
tPOWER-UP
1s
CONVERSION
INITIATED HERE
CONVERSION
INITIATED HERE
EXTERNAL REFERENCE
CONVERSION
INITIATED HERE
CONVERSION
INITIATED HERE
VDD
PD
CONVST
tPOWER-UP
ON-CHIP REFERENCE
25s
0
1321-
020
Figure 20. AD7822/AD7825 Power-Up Time
POWER VS. THROUGHPUT
Superior power performance can be achieved by using the
automatic power-down (Mode 2) at the end of a conversion
(see the Operating Modes section).
Figure 21 shows how the automatic power-down is implemented
using the CONVST signal to achieve the optimum power
performance for the AD7822/AD7825/AD7829. The duration
of the CONVST pulse is set to be equal to or less than the power-up
time of the devices (see the Operating Modes section). As the
throughput rate is reduced, the device remains in its power-
down state longer and the average power consumption over time
drops accordingly.
tPOWER-UP
1s
330ns
tCONVERT
POWER-DOWN
tCYCLE
10s @ 100kSPS
CONVST
0
1321-
0
22
Figure 21. Automatic Power-Down
For example, if the AD7822 is operated in a continuous
sampling mode, with a throughput rate of 100 kSPS and using
an external reference, the power consumption is calculated as
follows. The power dissipation during normal operation is
36 mW, VDD = 3 V. If the power-up time is 1 μs and the conversion
time is 330 ns (@ +25°C), the AD7822 can be said to dissipate
36 mW (maximum) for 1.33 μs during each conversion cycle.
If the throughput rate is 100 kSPS, the cycle time is 10 μs and
the average power dissipated during each cycle is (1.33/10) ×
(36 mW) = 4.79 mW. This calculation uses the minimum
conversion time, thus giving the best-case power dissipation at
this throughput rate. However, the actual power dissipated
during each conversion cycle could increase, depending on the
actual conversion time (up to a maximum of 420 ns).
Figure 22 shows the power vs. throughput rate for automatic
full power-down.
THROUGHPUT (kSPS)
100
10
0
5
0100
P
O
WE
R
(
m
W)
1
200
300
400
0.1
50
150
250
350
450
01
32
1-
0
23
Figure 22. AD7822/AD7825/AD7829 Power vs. Throughput
FREQUENCY (kHz)
0
–10
–80
(dB
)
–40
–50
–60
–70
–20
–30
0
113 14
2
170 198 22
7
255 283 31
2
34
0
368 396 42
5
453 481 51
0
53
8
566 595 62
3
651 680 70
8
73
6
765 793 82
1
850 878 90
6
93
5
963
28 57 85
991
2048 POINT FFT
SAMPLING
2MSPS
fIN = 200kHz
0
132
1-
0
24
Figure 23. AD7822/AD7825/AD7829 SNR
OPERATING MODES
The AD7822/AD7825/AD7829 have two possible modes of
operation, depending on the state of the CONVST pulse
approximately 100 ns after the end of a conversion, that is, upon
the rising edge of the EOC pulse.
Mode 1 Operation (High Speed Sampling)
When the AD7822/AD7825/AD7829 are operated in Mode 1,
they are not powered down between conversions. This mode of
operation allows high throughput rates to be achieved.
Figure 24 shows how this optimum throughput rate is achieved
by bringing CONVST high before the end of a conversion, that
is, before the EOC pulses low. When operating in this mode, a
new conversion should not be initiated until 30 ns after the end
of a read operation. This allows the track-and-hold to acquire
the analog signal to 0.5 LSB accuracy.
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