AD7490BRU(RevA) データシートの表示（PDF） - Analog Devices
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AD7490BRU Datasheet PDF : 24 Pages
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AD7490
Normal Mode (PM1 = PM0 = 1)
This mode is intended for the fastest throughput rate performance
as the user does not have to worry about any power-up times with
the AD7490 remaining fully powered at all times. Figure 12 shows
the general diagram of the operation of the AD7490 in this mode.
CS
1
SCLK
12
16
DOUT
CHANNEL IDENTIFIER BITS + CONVERSION RESULT
DIN
DATA IN TO CONTROL/SHADOW REGISTER
NOTES
1. CONTROL REGISTER DATA IS LOADED ON FIRST 12 SCLK CYCLES
2. SHADOW REGISTER DATA IS LOADED ON FIRST 16 SCLK CYCLES
Figure 12. Normal Mode Operation
The conversion is initiated on the falling edge of CS and the track
and hold will enter hold mode as described in the Serial Interface
section. The data presented to the AD7490 on the DIN line during
the first 12 clock cycles of the data transfer is loaded to the
Control Register (provided WRITE Bit is 1). If data is to be written to
the Shadow Register (SEQ ϭ 0, SHADOW ϭ1 on previous write),
data presented on the DIN line during the first 16 SCLK cycles is
loaded into the Shadow Register. The part will remain fully powered
up in Normal Mode at the end of the conversion as long as PM1
and PM0 are set to 1 in the write transfer during that conversion.
To ensure continued operation in Normal Mode, PM1 and PM0 are
both loaded with 1 on every data transfer. Sixteen serial clock
cycles are required to complete the conversion and access the
conversion result. The track and hold will go back into track on
the 14th SCLK falling edge. CS may then idle high until the next
conversion or may idle low until sometime prior to the next
conversion, (effectively idling CS low).
Once a data transfer is complete (DOUT has returned to three-
state WEAK/TRI Bit ϭ 0), another conversion can be initiated
after the quiet time, tQUIET, has elapsed by bringing CS low again.
Full Shutdown (PM1 = 1, PM0 = 0)
In this mode, all internal circuitry on the AD7490 is powered
down. The part retains information in the Control Register during
full shutdown. The AD7490 remains in full shutdown until
the power management bits in the Control Register, PM1 and
PM0, are changed.
If a write to the Control Register occurs while the part is in Full
Shutdown, with the power management bits changed to PM0 =
PM1 = 1, Normal Mode, the part will begin to power up on the CS
rising edge. The track and hold that was in hold while the part was
in Full Shutdown will return to track on the 14th SCLK falling edge.
To ensure that the part is fully powered up, tPOWER UP (t12)
should have elapsed before the next CS falling edge. Figure 13
shows the general diagram for this sequence.
Auto Shutdown (PM1 = 0, PM0 = 1)
In this mode, the AD7490 automatically enters shutdown at the
end of each conversion when the Control Register is updated.
When the part is in shutdown, the track and hold is in hold mode.
Figure 14 shows the general diagram of the operation of the
PART IS IN FULL
SHUTDOWN
CS
PART BEGINS TO POWER UP ON CS
RISING EDGE AS PM1 ؍1, PM0 ؍1
PART IS FULLY POWERED UP
ONCE TPOWER UP HAS ELAPSED
t12
1
SCLK
14 16
1
14 16
DOUT
CHANNEL IDENTIFIER BITS + CONVERSION RESULT
CS
1
SCLK
DIN
DATA IN TO CONTROL REGISTER
DATA IN TO CONTROL/SHADOW REGISTER
CONTROL REGISTER IS LOADED ON THE
FIRST 12 CLOCKS, PM1 ؍1, PM0 ؍1
TO KEEP PART IN NORMAL MODE, LOAD
PM1 ؍1, PM0 ؍1 IN CONTROL REGISTER
Figure 13. Full Shutdown Mode Operation
PART ENTERS
SHUTDOWN ON CS
RISING EDGE AS
PM1 ؍0, PM0 ؍1
PART BEGINS
TO POWER
UP ON CS
FALLING EDGE
PART IS FULLY
POWERED UP
DUMMY CONVERSION
16
1
16
1
PART ENTERS
SHUTDOWN ON CS
RISING EDGE AS
PM1 ؍0, PM0 ؍1
16
DOUT
CHANNEL IDENTIFIER BITS + CONVERSION RESULT
INVALID DATA
CHANNEL IDENTIFIER BITS + CONVERSION RESULT
DIN
DATA IN TO CONTROL/SHADOW REGISTER
DATA IN TO CONTROL/SHADOW REGISTER
CONTROL REGISTER IS LOADED ON THE
FIRST 12 CLOCKS, PM1 ؍0, PM0 ؍1
CONTROL REGISTER CONTENTS SHOULD
NOT CHANGE, WRITE BIT ؍0
TO KEEP PART IN THIS MODE, LOAD PM1 ؍0, PM0 ؍1
IN CONTROL REGISTER OR SET WRITE BIT = 0
Figure 14. Auto Shutdown Mode Operation
REV. A
–15–
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