SI4430-B1 Datasheet, PDF (52/74 Pages) Silicon Laboratories – Si4430/31/32 ISM TRANSCEIVER

Si4430/31/32-B1
8.3. General Purpose ADC
An 8-bit SAR ADC is integrated for general purpose use, as well as for digitizing the on-chip temperature sensor
reading. Registers 0Fh "ADC Configuration", 10h "Sensor Offset" and 4Fh "Amplifier Offset" can be used to
configure the ADC operation. Details of these registers are in “AN440: EZRadioPRO Detailed Register
Descriptions.”
Every time an ADC conversion is desired, bit 7 "adcstart/adcdone" in Register 0Fh “ADC Configuration” must be
set to 1. The conversion time for the ADC is 350 µs. After the ADC conversion is done and the adcdone signal is
showing 1, then the ADC value may be read out of “Register 11h: ADC Value." When the ADC is doing its
conversion, the adcstart/adcdone bit will read 0. When the ADC has finished its conversion, the bit will be set to 1.
A new ADC conversion can be initiated by writing a 1 to the adcstart/adcdone bit.
The architecture of the ADC is shown in Figure 27. The signal and reference inputs of the ADC are selected by
adcsel[2:0] and adcref[1:0] in register 0Fh “ADC Configuration”, respectively. The default setting is to read out the
temperature sensor using the bandgap voltage (VBG) as reference. With the VBG reference 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.
A differential multiplexer and amplifier are provided for interfacing external bridge sensors. The gain of the amplifier
is selectable by adcgain[1:0] in Register 0Fh. The majority of sensor bridges have supply voltage (VDD) dependent
gain and offset. The reference voltage of the ADC can be changed to either V_DD/2 or V_DD/3. A programmable V_DD
dependent offset voltage can be added using soffs[3:0] in register 10h.
Diff. MUX
Diff. Amp.
GPIO0
GPIO1
GPIO2
adcsel [2:0]
Temperature Sensor
aoffs [4:0] soffs [3:0]
adcgain [1:0]
Input MUX
V_DD / 3
V_DD / 2
V_BG (1.2V)
adcsel [2:0]
Ref MUX
8-bit ADC
V_in
V_ref
0 -1020mV / 0-255
adc [7:0]
adcref [1:0]
Figure 27. General Purpose ADC Architecture
Add R/W
0F R/W
Function/Description
ADC Configuration
D7
D6
D5
D4
D3
D2
D1
D0 POR Def.
adcstart/adcdone adcsel[2] adcsel[1] adcsel[0] adcref[1] adcref[0] adcgain[1] adcgain[0]
00h
10 R/W
Sensor Offset
soffs[3] soffs[2] soffs[1] soffs[0]
00h
11
R
ADC Value
adc[7]
adc[6] adc[5] adc[4]
adc[3]
adc[2]
adc[1]
adc[0]
—
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Rev 1.1