KP216K1409

Analog Absolute Pressure Sensor

Functional Description

Data Sheet

9

Revision 1.1, 2010-08-31

2

Functional Description

The pressure is detected by an array of capacitive surface micromachined sensor cells. The sensor cell output is

amplified, temperature compensated and linearized to obtain an output voltage that is proportional to the applied

pressure.

The transfer function for linearization is computed in the digital part of the sensor using a third order polynomial

calculation. The transfer function is created from the following parameters:

•

Minimum and maximum rated pressure

•

Voltage level at minimum and maximum rated pressure

•

Clamping levels

The output is analog and ratiometric with respect to the supply voltage.

All parameters needed for the complete calibration algorithm — such as offset, gain, temperature coefficients of

offset and gain, and linearization parameters — are determined after assembly. The parameters are stored in an

integrated E²PROM. The E²PROM content is protected with forward error correction (a one bit error is detected

and corrected, errors of more than one bit are detected and the output signal is switched to ground potential).

Clamping

The output voltage is limited internally to two clamping threshold levels. Based on this feature, the open bond

detection (OBD) is simplified and improved.

Open Bond Detection

The open bond detection, in conjunction with the clamping levels, eases the implementation of error and

malfunction detection strategies (e.g. for On-Board Diagnosis requirements). The microcontroller can sample the

output of the sensor and compare it with programmed overvoltage and undervoltage limits. When the sensor’s

output voltage exceeds those limits, a broken wire condition is identified.

When the chip is not powered properly, the JFET transistors of the broken wire detection stage are self-

conducting. For example, if the GND connection is interrupted, the output is drawn strongly to VDD. Similarly, if

the VDD connection is broken, the output is drawn to GND.