EVAL-AD7712EB View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
'EVAL-AD7712EB' PDF : 28 Pages View PDF
AD7712
PGA Gain
G2 Gl G0
00 0
00 1
01 0
01 1
10 0
10 1
11 0
11 1
Gain
1
2
4
8
16
32
64
128
(Default Condition after the Internal Power-On Reset)
Channel Selection
CH Channel
0 AIN1
1 AIN2
Low Level Input
High Level Input
(Default Condition after the Internal Power-On Reset)
Power-Down
PD
0 Normal Operation
1 Power-Down
(Default Condition after the Internal Power-On Reset)
Word Length
WL Output Word Length
0 16-Bit
1 24-Bit
(Default Condition after Internal Power-On Reset)
Burnout Current
BO
0
Off (Default Condition after Internal Power-On Reset)
1
On
Bipolar/Unipolar Selection (Both Inputs)
B/U
0 Bipolar (Default Condition after Internal Power-On Reset)
1 Unipolar
Filter Selection (FS11–FS0)
The on-chip digital filter provides a sinc3 (or (sinx/x)3) filter
response. The 12 bits of data programmed into these bits deter-
mine the filter cutoff frequency, the position of the first notch of
the filter, and the data rate for the part. In association with the
gain selection, it also determines the output noise (and therefore
the effective resolution) of the device.
The first notch of the filter occurs at a frequency determined by
the relationship filter first notch frequency = (fCLK IN/512)/code
where code is the decimal equivalent of the code in bits FS0 to
FS11 and is in the range 19 to 2,000. With the nominal fCLK IN of
10 MHz, this results in a first notch frequency range from 9.76 Hz
to 1.028 kHz. To ensure correct operation of the AD7712, the
value of the code loaded to these bits must be within this range.
Failure to do this will result in unspecified operation of the device.
Changing the filter notch frequency, as well as the selected gain,
impacts resolution. Tables I and II and Figure 2 show the effect
of the filter notch frequency and gain on the effective resolution
of the AD7712. The output data rate (or effective conversion
time) for the device is equal to the frequency selected for the
first notch of the filter. For example, if the first notch of the filter
is selected at 50 Hz, then a new word is available at a 50 Hz rate
or every 20 ms. If the first notch is at 1 kHz, a new word is avail-
able every 1 ms.
The settling time of the filter to a full-scale step input change is
worst case 4 ϫ 1/(output data rate). This settling time is to
100% of the final value. For example, with the first filter notch
at 50 Hz, the settling time of the filter to a full-scale step input
change is 80 ms max. If the first notch is at 1 kHz, the settling
time of the filter to a full-scale input step is 4 ms max. This
settling time can be reduced to 3 ϫ l/(output data rate) by syn-
chronizing the step input change to a reset of the digital filter. In
other words, if the step input takes place with SYNC low, the
settling time will be 3 ϫ l/(output data rate). If a change of
channels takes place, the settling time is 3 ϫ l/(output data rate)
regardless of the SYNC input.
The –3 dB frequency is determined by the programmed first
notch frequency according to the relationship filter –3 dB
frequency = 0.262 ϫ first notch frequency.
–10–
REV. F
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