ADC12_B Operation
873
SLAU367P – October 2012 – Revised April 2020
Copyright © 2012–2020, Texas Instruments Incorporated
ADC12_B
34.2.4 Auto Power Down
The ADC12_B is designed for low-power applications. When the ADC12_B is not actively converting, the
core is automatically disabled and automatically reenabled when needed. The MODOSC that sources
MODCLK is also automatically enabled when needed and disabled when not needed, if the ADC12VRSEL
selects the internal reference for the ADC.
If REFON=1, the internal reference is on continually; otherwise, it is only requested when an ADC
conversion is triggered. The REF buffer is powered down between conversions to save power unless
REFOUT=1, or pulse sample mode is used with ADC12MSC=1, or a conversion mode other than single-
channel single conversion is used. When the REF buffer is powered down in pulse sample mode, the ADC
sample time does not start until the REF buffer is ready (ADC12RDYIFFG=1), so the user does not need
to do anything. When the REF buffer is powered down in extended sample mode, the user must account
for the REF buffer settle/ready time by using the ADC12RDYIFFG=1 in calculating the time the trigger
should be asserted to make sure that the application meets the required sample time or ADC12_B
minimum sample time.
34.2.5 Sample Frequency Mode Selection
The ADC12PWRMD bit optimizes the ADC12_B power consumption at two ADC12CLK ranges. Select the
lowest ADC12CLK frequency that meets or exceeds the application requirements. If ADC12CLK is 1/4 or
less of data sheet specified maximum for ADC12PWRMD=0, ADC12PWRMD=1 may be set to save
power.
34.2.6 Sample and Conversion Timing
A rising edge of the sample input signal (SHI) initiates an analog-to-digital conversion. The sample input
signal can be inverted with the ADC12ISSH bit. The SHSx bits select the source for SHI and include the
following:
•
ADC12SC bit
•
Up to seven other sources that may include timer output (see to the device-specific data sheet for
available sources).
The ADC12_B supports 8-bit, 10-bit, and 12-bit resolution modes, and the ADC12RES bits select the
current mode. The analog-to-digital conversion requires 10, 12, and 14 ADC12CLK cycles, respectively.
The ADC12ISSH bit can invert the polarity of the SHI signal source. The SAMPCON signal controls the
sample period and start of conversion. When SAMPCON is high, sampling is active. The high-to-low
SAMPCON transition starts the analog-to-digital conversion after one clock cycle for pulse sample mode
and after one clock cycle plus a clock sync in extended sample mode. Control bit ADC12SHP defines the
sample-timing method, either extended sample mode or pulse mode. See the device-specific data sheet
for timers that are available for SHI sources.
34.2.6.1 Extended Sample Mode
ADC12SHP = 0 selects the extended sample mode. The SHI signal directly controls SAMPCON and
defines the length of the sample period t
sample.
If an ADC local reference buffer is used, the user should
assert the sample trigger, wait for the ADC12RDYIFG flag to be set (which indicates that the ADC12_B
local reference buffer is settled, and the flag does not occur if the sample trigger has not been asserted),
and then keep the sample trigger asserted for the desired sample period before de-asserting. Alternately,
if a local reference buffer is used, the user may assert the sample trigger for the desired sample time plus
the maximum time for the reference and buffers to settle (reference and buffer settling times are provided
in the device-specific data sheet). An ADC local reference buffer is used when ADC12VRSEL= 0001,
0011, 0101, 0111, 1001, 1011, 1101, or 1111. When SAMPCON is high, sampling is active. The high-to-
low SAMPCON transition starts the conversion after synchronization with ADC12CLK plus one clock cycle
(see
and