Datasheet

ADuC7060/ADuC7061 Data Sheet
Rev. D | Page 48 of 108
Bit Name Description
7 NOTCH2 Sinc3 modify. Set by user to modify the standard sinc3 frequency response to increase the filter stop-band rejection by
approximately 5 dB. This is achieved by inserting a second notch (NOTCH2) at
f
NOTCH2
= 1.333 × f
NOTCH
where f
NOTCH
is the location of the first notch in the response.
6:0 SF[6:0] Sinc3 decimation factor (SF).
1
The value (SF) written in these bits controls the oversampling (decimation factor) of the
sinc3 filter. The output rate from the sinc3 filter is given by
f
ADC
= (512,000/([SF + 1] × 64)) Hz
2
when the chop bit (Bit 15, chop enable) = 0 and the averaging factor (AF) = 0. This is valid for all SF values ≤ 125.
For SF = 126, f
ADC
is forced to 60 Hz.
For SF = 127, f
ADC
is forced to 50 Hz.
For information on calculating the f
ADC
for SF (other than 126 and 127) and AF values, refer to Table 46.
1
Due to limitations on the digital filter internal data path, there are some limitations on the combinations of the sinc3 decimation factor (SF) and averaging factor (AF)
that can be used to generate a required ADC output rate. This restriction limits the minimum ADC update in normal power mode to 4 Hz or 1 Hz in lower power mode.
2
In low power mode, the ADC is driven directly by the low power oscillator (131 kHz) and not 512 kHz. All f
ADC
calculations should be divided by 4 (approximately).
Table 46. ADC Conversion Rates and Settling Times
Chop
Enabled
Averaging
Factor
Running
Average
f
ADC
Normal Mode f
ADC
Low Power Mode t
SETTLING
1
No
No
No
64]1[
000,512
×+SF
64]1[
072,131
×+SF
ADC
f
3
No
No
Yes
64]1[
000,512
×+SF
64]1[
072,131
×+SF
ADC
f
4
No Yes No
]3[64]1[
000,512
AFSF +××+
]3[64]1[
072,131
AFSF +××+
ADC
f
1
No Yes Yes
]3[64]1[
000,512
AFSF +××+
]3[64]1[
072,131
AFSF +××+
ADC
f
2
Yes N/A N/A
3]3[64]1[
000,512
++××+ AFSF
3]3[64]1[
072,131
++××+ AFSF
ADC
f
2
1
An additional time of approximately 60 µs per ADC is required before the first ADC is available.
Table 47. Allowable Combinations of SF and AF
AF Range
SF
0
1 to 7
8 to 63
0 to 31
Yes
Yes
Yes
32 to 63
Yes
Yes
No
64 to 127 Yes No No