SX8724C Datasheet, PDF (31/67 Pages) Semtech Corporation – ZoomingADC for sensing data acquisition

SX8724C
ZoomingADC for sensing data acquisition
ADVANCED COMMUNICATIONS & SENSING
DATASHEET
resolution is truncated to 16 bit by the output register size, it may make sense to set OSR and N_ELCONV to higher values
in order to reduce the influence of the thermal noise in the PGA .
Table 17. Resolution¹ vs. SetOsr and SetNelconv settings
SetOsr
SetNelconv control bits
control bits
‘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
16
‘101‘
16
16
16
16
‘110‘
16
16
16
16
‘111‘
16
16
16
16
1. In shaded area, the resolution is truncated to 16 bits due to output register size RegA-
COut[15:0]
7.7.6 Conversion Time & Throughput
As explained in Figure 15, conversion time is given by:
T_CONV = (N_ELCONV ⋅ (OSR+1) +1) / f_S [s]
Equation 17
and throughput is then simply 1/TCONV. For example, consider an over-sampling ratio of 256, 2 elementary conversions,
and a sampling frequency of 500 kHz (SetOsr = "101", SetNelconv = "01" and SetFs = "00"). In this case, using Table 18,
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 illustrates the classic trade-off between resolution and conversion time.
Table 18. Normalized conversion time (Tconv x fs) vs. SetOsr and SetNelconv settings¹
SetNelconv control bits
SetOsr bits
NELCONV
OSR
‘00‘
‘01‘
‘10‘
‘11‘
1
2
4
8
‘000‘
10
19
37
73
‘001‘
18
‘010‘
34
‘011‘
66
35
69
137
67
133
265
131
261
521
Revision 1.01
© Semtech
January 2011
Page 31
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