XE8000EV104 Semtech, XE8000EV104 Datasheet - Page 98

• Manufacturer Part Number: XE8000EV104
• Description: EVAL BOARD FOR XE8805AMI028LF
• Manufacturer: Semtech
• Type: MCUr

Specifications of XE8000EV104

• Contents: Fully Assembled Evaluation Board
• For Use With/related Products: XE88LC05AMI028
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

16.6.1
Depending on the application objectives, the user may enable or bypass each PGA stage. This is done according to
the word ENABLE and the coding given in Table 16-13. To reduce power dissipation, the ADC can also be
inactivated while idle.
16.6.2
The first stage can have a buffer function (unity gain) or provide a gain of 10 (see Table 16-14). The voltage V
the output of PGA1 is:
where GD
16.6.3
The second PGA has a finer gain and offset tuning capability, as shown in Table 16-15 and Table 16-16. The
voltage V
where GD
PGA2_GAIN[1:0] and PGA2_OFFSET[3:0].
As shown in equation 6, the offset correction is directly proportional to the reference voltage. All drifts and
perturbations on the reference voltage will affect the precision of the offset compensation.
16.6.4
The finest gain and offset tuning is performed with the third and last PGA stage, according to the coding of Table
16-17 and Table 16-18. The output of PGA3 is also the input of the ADC. Thus, similarly to PGA2, we find that the
voltage entering the ADC is given by:
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.
As shown in equation 7, the offset correction is directly proportional to the reference voltage. All drifts and
perturbations on the reference voltage will affect the precision of the offset compensation.
© Semtech 2006
V
V
V
V
D2
D
D
IN
D
1
2
1
1
2
PGA & ADC Enabling
PGA1
PGA2
PGA3
,
3
is the gain of PGA1 (in V/V) controlled with the bit PGA1_GAIN.
,
ADC
at the output of PGA2 is given by:
and GDoff
=
=
V
and GDoff
D
GD
GD
2
=
<
1
GD
2
V
⋅
⋅
V
V
DD
IN
3
D
⋅
1
2
V
−
D
are respectively the gain and offset of PGA2 (in V/V). These are controlled with the words
(V)
GDoff
3
2
−
are respectively the gain and offset of PGA3 (in V/V). The control words are
GDoff
2
(V)
⋅
V
3
REF
⋅
V
REF
(V)
(V)
16-12
(Eq. 5)
(Eq. 6)
(Eq. 7)
(Eq. 8)
XE8805/05A
www.semtech.com
D1
at