AN3077 datasheet(41/82 Pages) STMICROELECTRONICS

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AN3077

Functional safety requirements for application software

Figure 10. Implementation of ADC_SW_TEST1 through the ADC presample feature

●

ADC_SWTEST_TEST2

To detect short failures two different voltages are acquired by the ADC. If these values

are different from the expected ones, a short failure on the multiplexed circuitry has

been detected.

To implement this test a presampling feature of the ADC can be exploited. The

presampling must be configured in such a way that the sampling of the channel is

bypassed and the presampling reference supply voltages are converted.

During the first step the VDD_HV_ADR0/1 is converted and compared with the its

expected value, then the VSS_HV_ADR0/1 is converted and compared with its expected

value (See Figure 12).

Figure 12 includes the conversion of the 2 different presampling reference voltages

(VDD_HV_ADR0/1 and VSS_VH_ADR0/1).

Note:

Rationale: To detect short failures of the channel multiplexing circuitry (See Figure 11)

Figure 11. Software BISTs to test the multiplexing circuitry (ADC_SWTEST_TEST2)

Note:

Implementation hint: The implementation hints of the ADC_SWTEST_TEST1 applies also

to the ADC_SWTEST_TEST2

To bypass the conversion of the input channel and convert the presampled values,

ADC_x_PSCR[PRECONV] register shall be set to 1.

Figure 12. Implementation of ADC_SW_TEST2 through the ADC presample feature

Convert

Ch A

Presample

Ch B

Sample

Ch B

Convert

Ch B

Presample

Ch A

Sample

Ch A

Vdd_HV_ADRx

Vss_HV_ADRx

Note: Either VDD_HV_ADR0/1 or VSS_HV_ADR0/1 can be used as presampling voltage.

ADC

Reference

value 2

pins

ADC

Reference

value 1

pins

ADC

Reference

value 1

First reference conversion

Short detection:

Second reference conversion

pins

Presample

Ch x

Convert

Ch x

Presample

Ch x

Convert

Ch x

Vdd_HV_ADRx

Vss_HV_ADRx

Note: Either VDD_HV_ADR0/1 or VSS_HV_ADR0/1 can be used as presampling voltage.

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