ZSSC3018 Datasheet

© 2020 Renesas Electronics Corporation

39

September 8, 2020

3.7 Calibration Sequence

Calibration essentially involves collecting raw signal and temperature data from the sensor-ZSSC3018 system for different known sensor-

element values (i.e., a resistive bridge or an absolute voltage source) and temperatures. This raw data can then be processed by the calibration

master (assumed to be the user’s computer), and the calculated calibration coefficients can then be written to on-chip memory.

Here is a brief overview of the three main steps involved in calibrating the ZSSC3018.

Assigning a unique identification to the ZSSC3018. This identification is written to shadow RAM and programmed in MTP memory. This unique

into a database stored on the calibration computer. This database will contain all the raw values of the connected sensor-element readings and

temperature readings for that part, as well as the known sensor-element measurand conditions and temperature to which the sensor-element

was exposed.

Data collection. Data collection involves getting uncorrected or raw data from the external sensor at different known measurand values and

temperatures. Then this data is stored on the calibration computer using the unique identification of the device as the index to the database.

Coefficient calculation and storage in MTP memory. After enough data points have been collected to calculate all the desired coefficients, the

coefficients can be calculated by the calibrating computer. Then the coefficients can be programmed to the MTP memory.

Result. The sensor signal and the characteristic temperature effect on output will be linearized according to the setup-dependent maximum

output range.

It is essential to perform the calibration with a fixed programming setup during the data collection phase. In order to prevent any accidental

incorrect processing, it is further recommended that the MTP memory setup is kept stable during the whole calibration process as well as in the

subsequent operation. A ZSSC3018 calibration only fits the setup used during its calibration. Changes of functional parameters after a

successful calibration can decrease the precision and accuracy performance of the ZSSC3018 as well as of the whole application.

Note: The ZSSC3018 supports operation with different sensor setups via the SM_config1 and SM_config2 registers. However, only one

calibration coefficient set is supported. Therefore, either an alternative ZSSC3218-external signal calibration using the alternate SM_config

settings must also be performed to ensure that the programmed SSC coefficients are valid for both setups, or a full reprogramming of the SSC

coefficients must be performed each time the sensor setup is changed. The selection of the external sensor setup (i.e., the AFE configuration)

3.7.1 Calibration Step 1 – Assigning Unique Identification

3.6.1. These two 16-bit registers allow for more than 4 billion unique devices.

3.7.2 Calibration Step 2 – Data Collection

The number of unique points (measurand and/or temperature) at which calibration must be performed generally depends on the requirements

of the application and the behavior of the sensor in use. The minimum number of points required is equal to the number of correction coefficients

to be corrected with a minimum of three different temperatures at three different sensor values. For a full calibration resulting in values for all 7

possible (external) sensor coefficients and 3 possible temperature coefficients, a minimum of 7 pairs of sensor with temperature measurements

must be collected.

Within this minimum field of 3 measurand measurements x 3 temperature measurements, data must be collected for the specific value pairs (at

known conditions) and then processed to calculate the coefficients. In order to obtain the potentially best and most robust coefficients, it is

recommended that measurement pairs (temperature vs. measurand) be collected at the outer corners of the intended operation range or at

least at points that are located far apart. It is also essential to provide highly precise reference values as nominal, expected values. The

measurement precision of the external calibration-measurement equipment should be ten times more accurate than the expected ZSSC3018

output accuracy after calibration in order to avoid accuracy losses caused by the nominal reference values (e.g., measurand signal and

temperature deviations).

Note: The coefficients SENS_shift and T_shift must not be determined during this calibration step.

Strong recommendation: Set these coefficients to zero until after initial calibration.