MLX90808 Datasheet, PDF (4/8 Pages) Melexis Microelectronic Systems – Absolute Integrated Pressure Sensor

MLX90808
Absolute Integrated Pressure Sensor
5 Diagnostic features
DC Operating Parameters T_A = -40^oC to 140^oC, V_DD = 5 V (unless otherwise specified)
Parameter
Symbol
Output when sensor is broken
Output when Vdd is broken
Output when Vdd is broken
Output when Vss is broken
Output when Vss is broken
Table 3: Diagnostic features
Test Conditions
Sensor broken
Pull up > 4k7
Pull down
Pull down > 10kΩ
Pull up
Min Typ Max Units
2
% Vdd
4
% Vdd
0
% Vdd
96
% Vdd
100
% Vdd
6 Detailed General Description
This chip integrates a pressure sensor and the associated signal conditioning on the same die. The supply
voltage V_DD directly supplies the pressure sensor.
The pressure sensing element consists of a square diaphragm realized in the silicon chip by backside
etching. Due to its small thickness this diaphragm reacts to a pressure difference at both of its side by
cambering. The internal strain increases, in particular at the border of the diaphragm. Here, the piezo-
resistive elements have been implanted into the silicon diaphragm, which act as transducer.
The piezo-resistive elements react to pressure induced changes of strain by changes in their resistance. Four
resistors are placed at all four borders of the square diaphragm. They are arranged in a Wheatstone-bridge.
A chopped instrumentation stage amplifies the differential output signal of the sensor. The gain of this
amplifier can be adjusted with 3 bits. After the input stage, there is a 3 bit programmable coarse offset which
is followed by a differential to single-ended conversion. The reference voltage for this stage is generated by a
10 bit DAC and varies linearly with temperature in order to perform the offset and offset drift compensation. A
digital hardware multiplier calculates this compensation. The temperature signal, serving as input for this
multiplier, is generated from the ADC of the output signal of the internal temperature sensor.
The chopped signal is demodulated with a switched capacitor stage. The buffered output serves as reference
for a 10 bit DAC to perform the span and span drift compensation. The DAC is controlled by the digital part.
Finally the signal is given out by a class AB rail-to-rail amplifier capable of sourcing and sinking large
currents.
A 3-point temperature and 2-point pressure calibration is required (room temperature, a low temperature and
a high temperature), to achieve an error less than ±1% over the complete pressure and temperature range
(the output error is referred to the output span).
PTC (Programming Through Connector) protocol is used to perform calibration.
The programming of the sensor chip is carried out via the analog connections (i.e. supply, ground, signal out).
No additional pins are necessary for calibration.
The output circuit is protected against short circuit to GND, Vbat (16V) and V_dd.
3901090808
Rev 001
Page 4 of 8
Data Sheet
Feb 08