Start
Sampling and
Clock Request
Stop
Sampling
Conversion
Complete
SAMPCON
SHI
t
sample
t
convert
t
phase
16 × ADC14CLK
Start
Conversion
ADC14CLK
Note: If internal ADC reference buffers are used, the SHI signal is gated while ADC14RDYIFG = 0.
t
clk
Data
Stored
t
dmove
Precision ADC Operation
847
SLAU356I – March 2015 – Revised June 2019
Copyright © 2015–2019, Texas Instruments Incorporated
Precision ADC
The regular-power mode (ADC14PWRMD = 00b) supports sampling rates up to 1 Msps and can be used
with any of the resolutions settings. The low-power mode (ADC14PWRMD = 10b) is a power saving mode
recommended for 12-, 10-, or 8-bit resolution settings with sampling rates not exceeding 200 ksps.
22.2.6 Sample and Conversion Timing
An analog-to-digital measurement is initiated with a rising edge of the sample input signal SHI. The source
for SHI is selected with the SHSx bits and includes the following:
•
ADC14SC bit
•
Up to seven other sources which may include timer output (see to the device-specific data sheet for
available sources).
When the sample input signal SHI is asserted, the Precision ADC clock is requested and after t
clk
(a
maximum of 3 cycles when SHI is generated based on the same clock source of the Precision ADC or 5
cycles when a different clock source is used to generate SHI signal), the request clock becomes available.
The analog-to-digital conversion requires 9, 11, 14 and 16 ADC14CLK cycles for 8-bit, 10-bit, 12-bit, and
14-bit resolution modes respectively. The polarity of the SHI signal source can be inverted with the
ADC14ISSH bit. 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. Once the conversion is complete, converted data is stored to ADC14MEMx register within 1
cycle ( t
dmove
). Two different sample-timing methods are defined by control bit ADC14SHP, extended
sample mode, and pulse mode. See the device-specific datasheet for available timers for SHI sources.
22.2.6.1 Extended Sample Mode
The extended sample mode is selected when ADC14SHP = 0. The SHI signal directly controls SAMPCON
and defines the length of the sample period t
sample.
If an ADC internal buffer is used, the application should
assert the sample trigger, wait for the ADC14RDYIFG flag to be set (indicating the Precision ADC local
buffered reference is settled), and then keep the sample trigger asserted for the desired sample period
before deasserting. Alternately, if an internal ADC buffer is used, the user may assert the sample trigger
for the desired sample time plus the max time for the reference and buffers to settle (reference and buffer
settling times are provided in the device-specific data sheet). The maximum sampling time must not
exceed 420 µs. An ADC internal buffer is used when ADC14VRSEL= 0001 or 1111. The high-to-low
SAMPCON transition starts the conversion after phase alignment with ADC14CLK (see
and
).
Figure 22-3. Extended Sample Mode in 14-Bit Mode