xe8802 Semtech Corporation, xe8802 Datasheet - Page 123

• Manufacturer Part Number: xe8802
• Description: Data Acquisition Soc With 16+10 Bit Zoomingadc? Embedded Risc Controller And Lcd Driver
• Manufacturer: Semtech Corporation

where GD
PGA3_GAIN[6:0] and PGA3_OFFSET[6:0] . To remain within the signal compliance of the PGA stages, the
condition:
must be verified.
related to V
where the total PGA gain is defined as:
and the total PGA offset is:
17.7 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 hereafter.
17.7.1
A conversion is started each time the bit START or the bit DEF is set. As depicted in Figure 17-5, a complete
analog-to-digital conversion sequence is made of a set of N
quantitative 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
properly.
© Semtech 2006
Finally, combining equations Eq. 5 to Eq. 7 for the three PGA stages, the input voltage V
V
V
V
T
GD
GDoff
ELCONV
IN
D
IN
1
Conversion Sequence
,
3
,
,
IN
TOT
ADC
ADC
sampling frequency f
over-sampling ratio OSR, and
number of elementary conversions N
V
and GDoff
by:
D
TOT
2
=
=
=
=
<
(
GD
GD
GD
OSR
=
V
GDoff
ELCONV
DD
3
3
TOT
⋅
⋅
+
V
GD
1
⋅
D
(V)
/ )
V
3
2
3
2
IN
f
−
≥ 2). A few additional clock cycles are also required to initiate and end the conversion
+
S
⋅
are respectively the gain and offset of PGA3 (in V/V). The control words are
GD
GDoff
−
GD
GDoff
1
3
(s)
⋅
S
GDoff
3
,
⋅
TOT
V
REF
⋅
V
2
(V/V)
REF
XE8802 Sensing Machine Data Acquisition MCU
(V)
(V)
(V/V)
ELCONV
17-11
.
ELCONV
with ZoomingADC™ and LCD driver
elementary incremental conversions and a final
(Eq. 7)
(Eq. 8)
(Eq. 9)
(Eq. 10)
(Eq. 11)
(Eq. 12)
S
=1/f
S
, i.e.:
IN,ADC
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of the ADC is