AD7715
Table IV. Output Update Rates
CLK*
0
0
0
0
1
1
1
1
FS1
0
0
1
1
0
0
1
1
FS0
0
1
0
1
0
1
0
1
Output Update Rate
20 Hz
25 Hz
100 Hz
200 Hz
50 Hz
60 Hz
250 Hz
500 Hz
–3 dB Filter Cutoff
5.24 Hz
6.55 Hz
26.2 Hz
52.4 Hz
13.1 Hz
15.7 Hz
65.5 Hz
131 Hz
Default Status
*Assumes correct clock frequency at MCLK IN pin
B/U
BUF
Bipolar/Unipolar Operation. A 0 in this bit selects Bipolar Operation. This is the default (Power-On or
RESET)
status of this bit. A 1 in this bit selects unipolar operation.
Buffer Control. With this bit low, the on-chip buffer on the analog input is shorted out. With the buffer
shorted out, the current flowing in the AV
DD
line is reduced to 250
µA
(all gains at f
CLK IN
= 1 MHz and gain
of 1 or 2 at f
CLK IN
= 2.4576 MHz) or 500
µA
(gains of 32 and 128 @ f
CLK IN
= 2.4576 MHz) and the output
noise from the part is at its lowest. When this bit is high, the on-chip buffer is in series with the analog input
allowing the input to handle higher source impedances.
Filter Synchronization. When this bit is high, the nodes of the digital filter, the filter control logic and the
calibration control logic are held in a reset state and the analog modulator is also held in its reset state. When
this bit goes low, the modulator and filter start to process data and a valid word is available in 3
×
1/(output
update rate), i.e., the settling-time of the filter. This FSYNC bit does not affect the digital interface and does
not reset the
DRDY
output if it is low.
FSYNC
Test Register (RS1, RS0 = 1, 0)
The part contains a Test Register which is used in testing the device. The user is advised not to change the status of any of the
bits in this register from the default (Power-On or RESET) status of all 0s as the part will be placed in one of its test modes and
will not operate correctly. If the part enters one of its test modes, exercising
RESET
will exit the part from the mode. An alterna-
tive scheme for getting the part out of one of its test modes, is to reset the interface by writing 32 successive 1s to the part and
then load all 0s to the Test Register.
Data Register (RS1, RS0 = 1, 1)
The Data Register on the part is a read-only 16-bit register which contains the most up-to-date conversion result from the
AD7715. If the Communications Register data sets up the part for a write operation to this register, a write operation must actu-
ally take place to return the part to where it is expecting a write operation to the Communications Register (the default state of
the interface). However, the 16 bits of data written to the part will be ignored by the AD7715.
REV. C
–11–
AD [ ANALOG DEVICES ]
