XE8000EV101 Semtech, XE8000EV101 Datasheet - Page 97

• 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

16.7 ADC Characteristics
The main performance characteristics of the ADC (resolution, conversion time, etc.) are determined by three
programmable parameters. The setting of these parameters and the resulting performances are described later.
16.7.1
A conversion is started each time the bit START or the bit DEF is set. As depicted in Figure 16-5, a complete analog-
to-digital conversion sequence is made of a set of N
quantization step. Each elementary conversion is made of (OSR+1) sampling periods T
The result is the mean of the elementary conversion results. An important feature is that the elementary conversions
are alternatively performed with the offset of the internal amplifiers contributing in one direction and the other to the
output code. Thus, converter internal offset is eliminated if at least two elementary sequences are performed (i.e. if
N
16.7.2
The word FIN[1:0] is used to select the sampling frequency f
RC-based frequency f
on oscillators and their control can be found in the clock block documentation.
© Semtech 2005
ELCONV
•
•
•
sampling frequency f
over-sampling ratio OSR, and
number of elementary conversions N
T
≥ 2). A few additional clock cycles are also required to initiate and end the conversion properly.
ELCONV
Conversion Sequence
Sampling Frequency
=
Conversion index
Table 16-19 Sampling frequency settings (f
(
OSR
+
RCEXT
1
/ )
Init
Offset
f
S
can be chosen. For FIN = "11", sampling frequency is about 8kHz. Additional information
S
Elementary
Conversion
,
(s)
1
+
Figure 16-5 Analog-to-digital conversion sequence
FIN[1:0]
T
ELCONV
00
01
10
11
Conversion
Elementary
ELCONV
= (OSR+1)/f
2
-
.
T
S
CONV
16-12
XE8801A, SX8801
Sampling Frequency f
ELCONV
and XE8805A
Conversion
Elementary
N
1/32⋅f
ELCONV
1/4⋅f
1/8⋅f
RC
∼8kHz
+
S
or f
elementary incremental conversions and a final
RC
RC
(Table 16-19). Three sub-multiples of the internal
RC
- 1
RCEXT
(Eq. 12)
Elementary
Conversion
is the RC oscillator frequency)
N
ELCONV
-
1/16⋅f
1/64⋅f
1/8⋅f
S
XE8802
∼4kHz
(Hz)
RCEXT
RCEXT
RCEXT
XE8801A – SX8801R
End
S
=1/f
Conversion
S
, i.e.:
Result
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