Automatic Pressure Range Operation - Infineon SP37 Function Manual

SP37
Tire Pressure Monitoring Sensor
ROM Library Functions
2.2.6

Automatic Pressure Range Operation

The Automatic Pressure Range feature is implemented as two separate pressure range calibrations within the
SP37 A5 device. One calibration is optimized for a "low range" of 100-500kPa, the other for a "high range" of 500-
900kPa. When the Automatic Pressure Range feature is enabled, the SP37 applies the calibration from the most
appropriate pressure range. For example, if the input pressure is within the low range, the low range calibration is
used to obtain the best measurement accuracy. The Automatic Pressure Range feature is only available when
compensated measurements are being performed.
The Automatic Pressure Range function includes a hysteresis feature to prevent "range toggling" at the boundary
between high range and low range calibrations. The hysteresis is implemented as an upper threshold, and a lower
threshold. During an Automatic Pressure Range measurement, if the input pressure is below the lower threshold
value, the lower range calibration is used during measurement. If the input pressure is above the higher threshold
value, the upper range calibration is used during measurement. If the input pressure is between the two threshold
values, the calibration range from the previous pressure measurement is used. The values of the hysteresis
thresholds may be either the Infineon default values, or values supplied as parameters to the pressure
measurement functions.
To apply the default hysteresis values when using Automatic Pressure Range, the [SensorConfig.10[ARANGE]]
bit within the [SensorConfig] parameter must be set to 1 , and the [SensorConfig.11[HYST]] bit within the
B
[SensorConfig] parameter must be cleared to 0 . For the 900kPa SP37 A5 device, the default upper threshold
B
value is 550kPa, and the default lower threshold value is 500kPa. When these default threshold values are used,
the pressure measurement error as specified within the SP37 A5 900kPa datasheet applies.
If the default hysteresis thresholds are not suitable, new threshold values may be supplied as parameters via the
[PressResult] array as shown in Table 16. In this case, both the [SensorConfig.10[ARANGE]] and
[SensorConfig.11[HYST]] bits within the [SensorConfig] parameter must be set to 1 . See Table 13 in
B
Chapter 2.2.4 for more details.
Note: If the lower hysteresis level is set to less than 500kPa, the measurement error is unspecified for input
pressures between the lower hysteresis threshold and 500kPa.
Note: The upper hysteresis level must not be set above 550kPa.
If Automatic Pressure Range is not desired, the pressure measurement function may be manually configured to
use only the high range or only the low range. In this case, the [SensorConfig.10[ARANGE]] bit within the
[SensorConfig] parameter must be cleared to 0 , and the [SensorConfig.9[PRANGE]] bit is used to select high
B
range calibration or low range calibration by being set to 1 or cleared to 0 , respectively.
B B
ROM Library Function Guide 36 Revision 1.0, 2011-12-15