XE8000EV101 Semtech, XE8000EV101 Datasheet - Page 100

• Manufacturer Part Number: XE8000EV101
• Description: EVAL BOARD FOR XE8801AMI027LF
• Manufacturer: Semtech
• Type: MCUr

Specifications of XE8000EV101

• Contents: Fully Assembled Evaluation Board
• For Use With/related Products: XE88LC01AMI027
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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
values in order to reduce the influence of the thermal noise in the PGA (see section 16.8.4).
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:
© Semtech 2005
Table 16-23 Normalized conversion time (T
T
CONV
Conversion Time & Throughput
Output Code Format
=
(
N
Figure 16-7 Resolution vs. normalized conversion time for different SET_NELC[1:0]
ELCONV
⋅
(
OSR
SET_OSR
+
[2:0]
000
001
010
011
100
101
110
111
) 1
+
1
/ )
CONV
f
S
16.0
14.0
12.0
10.0
(s)
8.0
6.0
4.0
1026
130
258
514
. For example, consider an over-sampling ratio of 256, 2 elementary
00
10
18
34
66
10.0
00
Normalized Conversion Time - T
01
to sampling period 1/f
SET_NELC[1:0]
1027
2051
131
259
515
10
01
19
35
67
CONV
100.0
11
16-15
⋅
SET_NELC
f
S
1029
2053
4101
) vs. SET_OSR[2:0] and SET_NELC[1:0](normalized
133
261
517
10
37
69
1000.0
1033
2057
4105
8201
137
265
521
11
73
CONV
(Eq. 16)
S
*f
)
S
[-]
10000.0
XE8801A – SX8801R
RC
= 2MHz, and FIN =
www.semtech.com
ELCONV
to higher