Specifications

ADC12D1000RF, ADC12D1600RF
SNAS519G –JULY 2011–REVISED APRIL 2013 www.ti.com
The power-on calibration will be not be performed if the CAL pin is logic-high at power-on. In this case, the
calibration cycle will not begin until the on-command calibration conditions are met. The
ADC12D1600/1000RF will function with the CAL pin held high at power up, but no calibration will be done
and performance will be impaired.
If it is necessary to toggle the CalDly Pin before the system power up sequence, then the CAL Pin/Bit
must be set to logic-high during the toggling and afterwards for 10
9
Sampling Clock cycles. This will
prevent the power-on calibration, so an on-command calibration must be executed or the performance will
be impaired.
6.3.3.4 On-command Calibration
In addition to the power-on calibration, it is recommended to execute an on-command calibration
whenever the settings or conditions to the device are altered significantly, in order to obtain optimal
parametric performance. Some examples include: changing the FSR via either ECM or Non-ECM, power-
cycling either channel, and switching into or out of DES Mode. For best performance, it is also
recommended that an on-command calibration be run 20 seconds or more after application of power and
whenever the operating temperature changes significantly, relative to the specific system performance
requirements.
Due to the nature of the calibration feature, it is recommended to avoid unnecessary activities on the
device while the calibration is taking place. For example, do not read or write to the Serial Interface or use
the DCLK Reset feature while calibrating the ADC. Doing so will impair the performance of the device until
it is re-calibrated correctly. Also, it is recommended to not apply a strong narrow-band signal to the analog
inputs during calibration because this may impair the accuracy of the calibration; broad spectrum noise is
acceptable.
6.3.3.5 Calibration Adjust
The sequence of the calibration event itself may be adjusted. This feature can be used if a shorter
calibration time than the default is required; see t
CAL
in Converter Electrical Characteristics Calibration.
However, the performance of the device, when using this feature is not ensured.
The calibration sequence may be adjusted via CSS (Addr: 4h, Bit 14). The default setting of CSS = 1b
executes both R
IN
and R
IN_CLK
Calibration (using Rtrim) and internal linearity Calibration (using Rext).
Executing a calibration with CSS = 0b executes only the internal linearity Calibration. The first time that
Calibration is executed, it must be with CSS = 1b to trim R
IN
and R
IN_CLK
. However, once the device is at
its operating temperature and R
IN
has been trimmed at least one time, it will not drift significantly. To save
time in subsequent calibrations, trimming R
IN
and R
IN_CLK
may be skipped, i.e. by setting CSS = 0b.
6.3.3.6 Read/Write Calibration Settings
When the ADC performs a calibration, the calibration constants are stored in an array which is accessible
via the Calibration Values register (Addr: 5h). To save the time which it takes to execute a calibration, t
CAL
,
or to allow re-use of a previous calibration result, these values can be read from and written to the register
at a later time. For example, if an application requires the same input impedance, R
IN
, this feature can be
used to load a previously determined set of values. For the calibration values to be valid, the ADC must be
operating under the same conditions, including temperature, at which the calibration values were originally
determined by the ADC.
To read calibration values from the SPI, do the following:
1. Set ADC to desired operating conditions.
2. Set SSC (Addr: 4h, Bit 7) to 1.
3. Read exactly 240 times the Calibration Values register (Addr: 5h). The register values are R0, R1, R2...
R239 where R0 is a dummy value. The contents of R<239:1> should be stored.
4. Set SSC (Addr: 4h, Bit 7) to 0.
48 Functional Description Copyright © 2011–2013, Texas Instruments Incorporated
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