Product Specs

Table Of Contents
37 SAADC Successive approximation analog-
to-digital converter
Page
358
PSEL_A
PSEL_A
PSEL_A
PSEL_A
PSEL_A
PSEL_A
PSEL_A
PSEL_A
PSEL_A
PSEL_A
PSEL_A
PSEL_A
PSEL_A
PSEL_A
PSEL_A
PSEL_A
PSEL_A
PSEL_A
RESULT = [V(P) V(N) ] * GAIN/REFERENCE * 2
(RESOLUTION - m)
CH[X].PSELP
CH[X].CONFIG
NC
AIN0
AIN1
AIN2
AIN3
AIN4
AIN5
AIN6
AIN7
VDD
ADC
RAM
MUX
P
RESULT
RESP
RESULT
RESULT
GAIN
SAR
core
EasyDMA
RESULT
NC
AIN0
AIN1
AIN2
AIN3
AIN4
AIN5
AIN6
AIN7
VDD
RESULT
N
RESULT
RESN
RESULT
RESULT
MUX
START
SAMPLE
STOP
VDD
Internal reference
REFSEL
STARTED
END
STOPPED
CH[X].PSELN
RESULT.PTR
Figure 98: Simplified ADC block diagram
Internally, the ADC is always a differential analog-to-digital converter, but by default it is configured with
single-ended input in the MODE field of the CH[n].CONFIG register. In single-ended mode, the negative
input will be shorted to ground internally.
The assumption in single-ended mode is that the internal ground of the ADC is the same as the external
ground that the measured voltage is referred to. The ADC is thus sensitive to ground bounce on the PCB in
single-ended mode. If this is a concern we recommend using differential measurement.
37.3 Digital output
The output result of the ADC depends on the settings in the CH[n].CONFIG and RESOLUTION registers as
follows:
where
V(P)
V(N)
GAIN
REFERENCE
is the voltage at input P
is the voltage at input N
is the selected gain setting
is the selected reference voltage
and m=0 if CONFIG.MODE=SE, or m=1 if CONFIG.MODE=Diff.
The result generated by the ADC will deviate from the expected due DC errors like offset, gain, differential
non-linearity (DNL), and integral non-linearity (INL). See Electrical specification for details on these
parameters. The result can also vary due to AC errors like non-linearities in the GAIN block, settling errors
due to high source impedance and sampling jitter. For battery measurement the DC errors are most
noticeable.