AMS 5105

Pressure sensor with one analog and two switching outputs

May 2012 - Rev. 2.0

Page 5/8

www.analogmicro.de

FUNCTIONAL DESCRIPTION

The pressure sensors/pressure switches in the AMS 5105 series combine a high-quality piezoresistive

silicon sensing element with a modern, mixed-signal CMOS ASIC for signal conditioning with full digital

correction on a ceramic substrate. This enables high-precision measurements and excellent drift and long-

term stability.

The functional principle of the AMS 5105 is explained in Figure 1.

The physical pressure is measured at AMS 5105's piezoresistive pressure sensing element where the

pressure is converted into a differential voltage signal which is almost proportional to the pressure. This

differential voltage signal is corrected and conditioned by the ASIC in multiple steps.

Firstly, the differential voltage signal from the sensing element is pre-amplified by the amplifier and

transmitted by a multiplexer to the A/D converter (ADC). The ADC converts the signal into digital values with

a resolution of 14 bits. The digitized signal is corrected and calibrated in the follow-on ASIC microcontroller.

Factory precision calibration of AMS 5105 sets the sensor-specific correction coefficients and stores these in

the EEPROM for each sensor. This permits sensor-specific calibration and correction (i.e. temperature

compensation and linearization) of the digitized pressure signal. The temperature signal necessary for

temperature compensation is also measured at the piezoresistive measuring cell and is transmitted by the

multiplexer to the ADC, where it is digitized. The ASIC microcontroller runs a cyclic program which

continuously calculates the current standardized and corrected digital pressure values.

To generate the analog output signal the corrected digital pressure value is converted into an analog voltage

by an 11-bit D/A converter (DAC). The standardized analog output voltage (0.5…4.5 V) at the sensor's PIN 4

(VOUT) is ratiometric to the supply voltage.

The logic output signals at the sensor's switching outputs PIN 8 (SWITCH 1) and PIN 7 (SWITCH 2) are

generated by the ASIC's programmable comparator. This compares the corrected digital pressure value with

the specific threshold and hysteresis values programmed and stored in the EEPROM. Depending on the

selected configuration mode for the particular switching output the logic output signal is set to high or low.

The configuration setting (normally open, normally closed or window mode) and the settings of the particular

thresholds, hysteresis and delay for the two switching outputs are stored in the EEPROM. These settings are

changed by programming with the AMS 5105 starter kit via the sensor's programming interface at PIN 5

(SDA) and PIN 6 (SCL).

ADC

uC

DAC

EEPROM

Buffer

pressure

sensing

element

TSig

Amp

MUX

3

7

8

2

4

AMS 5105

Switch2

Switch1

VCC

GND

COMP

6

5

SDA SCL

SIF

Programming

Figure 1: Functional principle of AMS 5105