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參數(shù)資料
| 型號(hào)： | EVAL-AD7887CB |
| 廠(chǎng)商： | Analog Devices, Inc. |
| 英文描述： | +2.7 V to +5.25 V, Micropower, 2-Channel, 125 kSPS, 12-Bit ADC in 8-Lead uSOIC |
| 中文描述： | 2.7 V至5.25 V，微功耗，2通道，125 kSPS的，12位ADC的8引腳uSOIC |
| 文件頁(yè)數(shù)： | 12/16頁(yè) |
| 文件大?。?/td> | 133K |
| 代理商： | EVAL-AD7887CB |
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REV. B
AD7887
–12–
Mode 3 (PM1 = 1, PM0 = 0)
In this mode, the AD7887 automatically enters its full shutdown
mode at the end of every conversion. It is similar to Mode 1
except that the status of
CS
does not have any effect on the
power-down status of the AD7887.
Figure 15a shows the general diagram of the operation of the
AD7887 in this mode. On the first falling SCLK edge after
CS
goes low, all on-chip circuitry starts to power up. It takes ap-
proximately, 5
μ
s for the AD7887 internal circuitry to be fully
powered up. As a result, a conversion (or sample-and-hold
acquisition) should not be initiated during this 5
μ
s. T he input
signal is sampled on the second rising edge of SCLK following
the
CS
falling edge. T he user should ensure that 5
μ
s elapses
between the first falling edge of
SCLK
and the second rising
edge of SCLK after the
CS
falling edge as shown in Figure 15a.
In microcontroller applications (or with a slow serial clock) this
is readily achievable by driving the
CS
input from one of the
port lines and ensuring that the serial data read (from the micro-
controller’s serial port) is not initiated for 5
μ
s. However, for
higher speed serial clocks it will not be possible to have a 5
μ
s
delay between powering up and the first rising edge of the SCLK .
T herefore, the user will need to write to the Control Register to
exit this mode and (by writing PM1 = 0 and PM0 = 1) put the
part into Mode 2. A second conversion will then need to be
initiated when the part is powered up to get a conversion result, as
shown in Figure 15b. T he write operation that takes place in
conjunction with this second conversion can put the part back
into Mode 3 and the part will go into power-down mode when
the conversion sequence ends.
Mode 4 (PM1 = 1, PM0 = 1)
In this mode, the AD7887 automatically enters a standby (or
sleep) mode at the end of every conversion. In this standby
mode, all on-chip circuitry, apart from the on-chip reference, is
powered down. T his mode is similar to Mode 3 but in this case,
the power-up time is much shorter as the on-chip reference
remains powered up at all times.
Figure 16 shows the general diagram of the operation of the
AD7887 in this mode. On the first falling SCLK edge after
CS
goes low, the AD7887 comes out of standby. T he AD7887
wake-up time is very short in this mode so it is possible to wake-
up the part and carry out a valid conversion in the same read/
write operation. T he input signal is sampled on the second
rising edge of SCLK following the
CS
falling edge. At the end of
conversion (last rising edge of SCLK ) the part automatically
enters its standby mode.
SCLK
CS
DOUT
DIN
THE PART POWERS UP FROM
SHUTDOWN ON SCLK FALLING EDGE AS
PM1 = 1 AND PM0 = 0
1
16
1
16
2
t
10
= 5
m
s
THE PART ENTERS
SHUTDOWN AT THE END OF
CONVERSION AS PM1 = 1 AND PM0 = 0
CONTROL REGISTER DATA IS LOADED ON THE
FIRST 8 CLOCKS. PM1 = 1 AND PM0 = 0
PM1 = 1 AND PM0 = 0 TO KEEP THE
PART IN THIS MODE
DATA IN
DATA IN
4 LEADING ZEROS + CONVERSION RESULT
4 LEADING ZEROS + CONVERSION RESULT
Figure 15a. Mode 3 Operation
SCLK
CS
DOUT
DIN
1
16
8
1
16
8
1
16
8
PM1 = 0 AND PM0 = 1 TO PLACE
THE PART IN NORMAL MODE
PM1 = 1 AND PM0 = 0 TO PLACE
THE PART BACK IN MODE 3
CONTROL REGISTER DATA IS LOADED ON
THE FIRST 8 CLOCKS. PM1 = 1 AND PM0 = 0
THE PART ENTERS
SHUTDOWN AT THE END
OF CONVERSION AS
PM1 = 1 AND PM0 = 0
THE PART REMAINS POWERED UP
AS PM1 = 0 AND PM0 = 1
THE PART BEGINS TO POWER
UP FROM SHUTDOWN
THE PART ENTERS
SHUTDOWN AT THE END OF
CONVERSION AS PM1 = 1
AND PM0 = 0
4 LEADING ZEROS
+ CONVERSION RESULT
DATA IN
4 LEADING ZEROS
+ CONVERSION RESULT
DATA IN
4 LEADING ZEROS
+ CONVERSION RESULT
DATA IN
Figure 15b. Mode 3 Operation
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| EVAL-AD7887CB4 | 制造商:AD 制造商全稱(chēng):Analog Devices 功能描述:2.7 V to 5.25 V, Micropower, 2-Channel, 125 kSPS, 12-Bit ADC in 8-Lead MSOP |
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| EVAL-AD7888CB | 制造商:Analog Devices 功能描述:EVAL KIT FOR 2.7 V TO 5.25 V, MICROPWR, 8CH, 125 KSPS, 12-BI - Bulk |
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