XE8805 SEMTECH [Semtech Corporation], XE8805 Datasheet - Page 102

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

16.7.6
As explained using Figure 16-5, conversion time is given by:
and throughput is then simply 1/T
conversions, and a sampling frequency of 500kHz (SET_OSR = "101", SET_NELC = "01", f
"00"). In this case, using Table 16-23, the conversion time is 515 sampling periods, or 1.03ms. This corresponds to
a throughput of 971Hz in continuous-time mode. The plot of Figure 16-7 illustrates the classic trade-off between
resolution and conversion time.
16.7.7
The ADC output code is a 16-bit word in two's complement format (see Table 16-24). For input voltages outside the
range, the output code is saturated to the closest full-scale value (i.e. 0x7FFF or 0x8000). For resolutions smaller
than 16 bits, the non-significant bits are forced to the values shown in Table 16-25. The output code, expressed in
LSBs, corresponds to:
Recalling equation Eq. 9, this can be rewritten as:
© Semtech 2006
T
OUT
CONV
Conversion Time & Throughput
Output Code Format
ADC
=
(
Figure 16-7. Resolution vs. normalized conversion time for different SET_NELC[1:0]
N
=
ELCONV
2
16
Table 16-23. Normalized conversion time (T
⋅
V
⋅
V
IN
(
OSR
REF
,
ADC
SET_OSR
[2:0]
+
⋅
000
001
010
011
100
101
110
111
) 1
OSR
OSR
+
SET_NELC[1:0](normalized to sampling period 1/f
1
/ )
+
CONV
1
f
S
16.0
14.0
12.0
10.0
8.0
6.0
4.0
(s)
(LSB)
1026
. For example, consider an over-sampling ratio of 256, 2 elementary
130
258
514
10.0
00
10
18
34
66
00
Normalized Conversion Time - T
01
SET_NELC[1:0]
1027
2051
10
131
259
515
01
19
35
67
100.0
11
16-16
SET_NELC
1029
2053
4101
133
261
517
10
37
69
1000.0
CONV
1033
2057
4105
8201
CONV
137
265
521
11
73
(Eq. 16)
(Eq.17)
⋅
*f
f
S
S
) vs. SET_OSR[2:0] and
[-]
10000.0
S
)
RC
XE8805/05A
= 2MHz, and FIN =
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