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Si4430
Preliminary Rev. 0.4
55
8.3. General Purpose ADC
An 8-bit SAR ADC is integrated onto the chip for general purpose use, as well as for digitizing the temperature
sensor reading. “Register 0Fh. ADC Configuration,” on page 93 must be configured depending on the use of the
GP ADC before use. The architecture of the ADC is demonstrated in Figure 24. First the input of the ADC must be
selected by setting the ADCSEL[2:0] depending on the use of the ADC. For instance, if the ADC is going to be
used to read out the internal temperature sensor, then ADCSEL[2:0] should be set to 000. Next, the input reference
voltage to the ADC must be chosen. By default, the ADC uses the bandgap voltage as a reference so the input
range of the ADC is from 0–1.02 V with an LSB resolution of 4 mV (1.02/255). Changing the ADC reference will
change the LSB resolution accordingly.
Every time the ADC conversion is desired, the ADCStart bit in “Register 0Fh. ADC Configuration,” on page 93 must
be set to 1. This is a self clearing bit that will be cleared at the end of the conversion cycle of the ADC. The
conversion time for the ADC is 350 us. After the 350 us or when the ADCstart/busy bit is cleared, then the ADC
value may be read out of "Register 11h. ADC Value". Setting the "Register 10h. ADC Sensor Amplifier Offset", ADC
Sensor Amplifier Offset is only necessary when the ADC is configured to used as a Bridge Sensor as described in
the following section.
Figure 24. General Purpose ADC Architecture
Add R/W
Function/Description
D7
D6
D5
D4
D3
D2
D1
D0
POR Def.
0F
R/W
ADC Configuration
adcstart/adcbusy
adcsel[2] adcsel[1] adcsel[0]
adcref[1]
adcref[0]
adcgain[1] adcgain[0]
00h
10
R/W
ADC Sensor Amplifier Offset
adcoffs[3]
adcoffs[2]
adcoffs[1]
adcoffs[0]
00h
11
R
ADC Value
adc[7]
adc[6]
adc[5]
adc[4]
adc[3]
adc[2]
adc[1]
adc[0]
—
……
……
……
Diff. MUX
Diff. Amp.
Input MUX
Ref MUX
Vin
Vref
……
ADCSEL<2:0>
OTR<3:0>
GAIN<1:0>
ADCSEL<2:0>
REFSEL<1:0>
VMEAS<7:0>
V
BAT
/ 3
V
BAT
/ 2
GPIO1
GPIO0
GPIO2
TS
V
BG
(1.2V)
8-bit ADC
0-1020mV / 0-255