![](http://datasheet.mmic.net.cn/Semtech/XE8805AMI028LF_datasheet_100002/XE8805AMI028LF_101.png)
Semtech 2006
www.semtech.com
16-15
XE8805/05A
SET_NELC[1:0]
(RegAcCfg0[6:5])
# of Elementary
Conversions
NELCONV (-)
00
1
01
2
10
4
11
8
Table 16-21. Number of elementary conversion settings
As already mentioned, NELCONV must be equal or greater than 2 to reduce internal amplifier offsets.
16.7.5
Resolution
The theoretical resolution of the ADC, without considering thermal noise, is given by:
)
(
log
)
(
log
2
ELCONV
N
OSR
n
+
=
(Bits)
(Eq. 15)
5
7
9
11
13
15
17
000
001
010
011
100
101
110
111
SET_OSR
R
e
s
o
lu
ti
o
n
-
n
[B
it
s
]
11
10
01
00
SET_NELC=
Figure 16-6. Resolution vs. SET_OSR[2:0] and SET_NELC[2:0]
SET_NELC
SET_OSR
[2:0]
00
01
10
11
000
6
7
8
9
001
8
9
10
11
010
10
11
12
13
011
12
13
14
15
100
14
15
16
101
16
110
16
111
16
(shaded area: resolution truncated to 16 bits
due to output register size RegAcOut[15:0])
Table 16-22. Resolution vs. SET_OSR[2:0] and SET_NELC[1:0] settings
Using look-up Table 16-22 or the graph plotted in Figure 16-6, resolution can be set between 6 and 16 bits. Notice
that, because of 16-bit register use for the ADC output, practical resolution is limited to 16 bits, i.e. n
≤ 16. Even
if the resolution is truncated to 16 bit by the output register size, it may make sense to set OSR and NELCONV to
higher values in order to reduce the influence of the thermal noise in the PGA (see section 16.8.4).
Not
Recommended
for
New
Designs