CC2480_11 Datasheet, PDF (26/48 Pages) Texas Instruments – Z-Accel 2.4 GHz ZigBee Processor

In addition to the input pins A0-1, the output of
an on-chip temperature sensor can be
selected as an input to the ADC for
temperature measurements.
9.3.2.4 ADC Operating Modes
This section describes the operating modes
and initialization of conversions.
The ADC uses an internal voltage reference
for single-ended conversions.
9.3.2.5 ADC Conversion Results
The digital conversion result is represented in
two's complement form. The result is always
positive. This is because the result is the
difference between ground and input signal
which is always posivitely signed
(Vconv=Vinp-Vinn, where Vinn=0V). The
maximum value is reached when the input
amplitude is equal VREF, the internal voltage
reference.
9.3.2.6 ADC Reference Voltage
The positive reference voltage for analog-to-
digital conversions is an internally generated
1.25V voltage.
9.3.2.7 ADC Conversion Timing
The ADC is run on the 32MHz system clock,
which is divided by 8 to give a 4 MHz clock.
The time required to perform a conversion
depends on the selected decimation rate.
When the decimation rate is set to for instance
128, the decimation filter uses exactly 128 of
the 4 MHz clock periods to calculate the result.
When a conversion is started, the input
CC2480
It is also possible to select a voltage
corresponding to AVDD_SOC/3 as an ADC
input. This input allows the implementation of
e.g. a battery monitor in applications where
this feature is required.
The decimation rate (and thereby also the
resolution and time required to complete a
conversion and sample rate) is configurable
from 7-12 bits.
For differential configurations the difference
between the pins is converted and this
difference can be negatively signed. For 12-bit
resolution the digital conversion result is 2047
when the analog input, Vconv, is equal to
VREF, and the conversion result is -2048
when the analog input is equal to –VREF.
multiplexer is allowed 16 4 MHz clock cycles to
settle in case the channel has been changed
since the previous conversion. The 16 clock
cycles settling time applies to all decimation
rates. Thus in general, the conversion time is
given by:
Tconv = (decimation rate + 16) x 0.25 µs.
CC2480 Data Sheet SWRS074
Page 26 of 43