XE8805 SEMTECH [Semtech Corporation], XE8805 Datasheet - Page 101

• Manufacturer Part Number: XE8805
• Description: Data Acquisition MCU
• Manufacturer: SEMTECH [Semtech Corporation]

As already mentioned, N
16.7.5
The theoretical resolution of the ADC, without considering thermal noise, is given by:
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 N
higher values in order to reduce the influence of the thermal noise in the PGA (see section 16.8.4).
© Semtech 2006
n
=
Resolution
2
⋅
log
2
(
OSR
Table 16-22. Resolution vs. SET_OSR[2:0] and SET_NELC[1:0] settings
)
+
ELCONV
log
Figure 16-6. Resolution vs. SET_OSR[2:0] and SET_NELC[2:0]
2
(
SET_OSR
N
[2:0]
Table 16-21. Number of elementary conversion settings
must be equal or greater than 2 to reduce internal amplifier offsets.
ELCONV
000
001
010
011
100
101
110
111
(RegAcCfg0[6:5])
SET_NELC[1:0]
)
due to output register size RegAcOut[15:0])
(shaded area: resolution truncated to 16 bits
(Bits)
00
01
10
11
17
15
13
11
9
7
5
000
00
10
12
14
16
16
16
6
8
SET_NELC=
001
010
01
11
13
15
16
16
16
7
9
SET_NELC
11
10
01
00
16-15
SET_OSR
011
# of Elementary
Conversions
N
10
10
12
14
16
16
16
16
ELCONV
100
8
1
2
4
8
101
(-)
11
11
13
15
16
16
16
16
110
9
(Eq. 15)
111
XE8805/05A
www.semtech.com
ELCONV
to