DigitalResult
4096
x(InputVoltage
- AD
)
REFLO
(AD
- AD
)
REFHI
REFLO
---------------------------------------------------------------------------------------
0.5
–
=
DigitalResult
1024
x (InputVoltage - AD
)
REFLO
AD
- AD
REFHI
REFLO
---------------------------------------------------------------------------------------
0.5
–
=
Overview
852
SPNU563A – March 2018
Copyright © 2018, Texas Instruments Incorporated
Analog To Digital Converter (ADC) Module
22.1.1.1 Input Multiplexor
The input multiplexor (MUX) connects the selected input channel to the AIN input of the ADC core. The
ADC1 module supports up to 32 inputs as shown in
. The ADC2 module supports up to 25
inputs. The sequencer selects the channel to be converted. Enabling the enhanced channel selection
mode also allows one or more of the analog input channels to be connected to the output of an external
analog switch or multiplexor.
22.1.1.2 Self-Test and Calibration Cell
The ADC includes specific hardware that allows a software algorithm to detect open/short on an ADC
analog input. It also allows the application program to calibrate the ADC. Also see
and
22.1.1.3 Analog-to-Digital Converter Core
The ADC core is a combination voltage scaling, charge redistribution Successive Approximation Register
(SAR) based analog-to-digital converter. The core can be configured for operation in 10-bit resolution
(default) or 12-bit resolution. This is controlled by the sequencer logic. This selection applies to all
conversions performed by the ADC module. It is not possible to convert some channels with a 12-bit
resolution and some with a 10-bit resolution.
A single conversion from an analog input to a digital conversion result occurs in two distinct periods:
•
Sampling Period:
–
The sequencer generates a START signal to the ADC core to signal the start of the sampling
period.
–
The analog input signal is sampled directly on to the switched capacitor array during this period,
providing an inherent sample-and-hold function.
–
The sampling period ends one full ADCLK after the falling edge of the START signal.
–
The sequencer can control the sampling period duration by configuring the conversion group’s
sample time control register (ADEVSAMP, ADG1SAMP, ADG2SAMP). This register controls the
time for which the START signal stays high.
•
Conversion Period:
–
The conversion period starts one full ADCLK after the falling edge of START.
–
One bit of the conversion result is output on each rising edge of ADCLK in the conversion period,
starting with the most-significant bit first.
–
The conversion period is 12 ADCLK cycles in case of a 12-bit ADC, and is 10 ADCLK cycles in
case of a 10-bit ADC.
–
The ADC core generates an End-Of-Conversion (EOC) signal to the sequencer at the end of the
conversion period. At this time the complete 12-, or 10-bit conversion result is available.
–
The sequencer captures the ADC core conversion result output as soon as EOC is driven High.
The analog conversion range is determined by the reference voltages: AD
REFHI
and AD
REFLO
. AD
REFHI
is the
top reference voltage and is the maximum analog voltage that can be converted. An analog input voltage
equal to AD
REFHI
or higher results in an output code of 0x3FF for 10-bit resolution and 0xFFF for 12-bit
resolution. AD
REFLO
is the bottom reference voltage and is the minimum analog voltage that can be
converted. Applying an input voltage equal to AD
REFLO
or lower results in an output code of 0x000. Both
AD
REFHI
and AD
REFLO
must be chosen not to exceed the analog power supplies: V
CCAD
and V
SSAD
,
respectively. Input voltages between AD
REFHI
and AD
REFLO
produce a conversion result given by
for 10-bit resolution and by
for 12-bit resolution.
(27)
(28)