L9396 datasheet(64/109 Pages) STMICROELECTRONICS

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System functional safety implementations

L9396

64/109

DS12539 Rev 6

System functional safety implementations

7.1

General functional safety implementations

The device comes with a set of analog and digital design implementations:



Double independent voltage reference;



Oscillator clock monitoring;



Battery monitoring;



ECU supply voltage monitoring;



Internal (more than 30 channels) and external (up to 7 channels) analog voltage

measurements;



Double watchdog control;



Pump motor driver diagnostics;



Reset output pin;



Fault output pin;



Fail-safe configurable output pin;



Analog BIST on all analog voltage monitors;



Digital BIST;



Over temperature protection;



Temperature sensor

7.2

System monitoring and reset handling

7.2.1

Analog to Digital algorithmic converter

The device hosts an integrated 10-bit Analog to Digital converter, running at a clock

frequency of 16MHz. The ADC output is processed by a D to D converter with the following

functions:



Use of trimming bits to recover additional gain error due to resistor dividers mismatch;



Digital low-pass filtering;



Conversion from 12 to 10 bits.

10-bit data are filtered inside the digital section. The number of samples that are filtered vary

depending on the chosen conversion. The sample number can be configured by accessing

the ADC_CFG register. After low pass filter, the residual total error is +/-5 LSB. This error

figure applies to the case of a precise reference voltage: the spread of reference voltage

causes a proportional error in the conversion output.

The reference voltage of the ADC VREFH is set to 2.5 V and VREFL set to 0.1 V. Therefore

the voltage range is 2.4 V.

The conversion time is comprised of several factors: the number of measurements loaded

into the queue, the number of samples taken for any measurement, and the various settling

times. An example of conversion time calculation for a full ADC request queue is reported in

Figure 10. The timings reported in Figure 10 are nominal ones, min/max values can be

obtained by considering the internal oscillator frequency variation reported in the DC

characteristics section.

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