MLX90809 Datasheet, PDF (5/11 Pages) Melexis Microelectronic Systems – Relative Pressure Sensor

MLX90809
Relative Pressure Sensor
7 Detailed General Description
The pressure sensing element consists of a square diaphragm realized in the silicon chip by backside
etching. The diaphragm reacts to a pressure difference between the top and bottom side of the diaphragm.
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 a transducer.
The electronics front end amplifies the signal from the bridge, performs a coarse offset compensation and an
ADC conversion. The DSP performs the compensations over temperature. Furthermore, the digital circuit
provides some filtering, the possibility to linearize the pressure signal and also implements the clamping
function. The analog back end consists of a 12 bit DAC and an output driver. This chip delivers an analog
output proportional to the pressure or a SENT output compliant with SAE J2716 spec dated January 2010.
A broken wire detection block allows actively driving the output to one of the rails in case of a broken supply
or ground connection. Extensive protection of the supply lines allows the MLX90809 to handle extreme
overvoltage conditions and is immune to severe external disturbances. Several diagnostic functions (over-
voltage, under-voltage, overpressure, under pressure detections) have been implemented on the 90809 and
can be enabled by programming EEPROM settings. Figure 2 describes MLX90809 block diagram.
Piezoresistive
sensing element
Temperature
sensor
Gain & Offset
compensation
OPA
Diagnostic signals
Broken wire
Test
detection
DSP
Micro controller
Gain & Offset temperature
M
ADC
U
16 bits
compensation
Pressure Linearization
X
Programmable filter
Diagnostics Logic
Rom
FW
EE
PROM
Ram
Figure 2: MLX90809 block diagram
Overvoltage &
reverse voltage
protection
Vext
Analog & Digital
Regulator and
POR
DAC
12 bits
Analog driver
Analog
Gain
Output
Slew
rate
control
SENT driver
SENT
Output
Ground
Rev 002
390109080901
Page 5 of 11
Data Sheet
Oct/14