VNF9Q20F datasheet(70/109 Pages) STMICROELECTRONICS

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Safety-related functions

Two built-in self-tests (BIST) have been implemented in VNF9Q20F to automatically check the ADC conversion

and I²t comparators health along the device working life. The two BISTs are contemporarily executed, as soon as

VCC is present (the device leaves the start phase).

9.1

ADC BIST

At each power on reset, the digital part executes the ADC BIST. During the execution of that sequence, current

sense reading is disabled and a multiplexer will pass a low reference current IBIST_MIN for combination <0, 0>, a

medium reference current IBIST_MID for combination <0, 1> and a high reference current IBIST_MAX for

combination <1, 0>.

Table 44. ADC built in self-test

adc_bist <1>

adc_bist <0>

IBIST

Expected analog current

Low

50 µA

Mid

200 µA

High

550 µA

IVFRAME

Dependent on frame temperature

The ADC conversion results are stored into three distinct R&C registers:

•

Address 0x32h - Digital Current for self-test (Low Level) (ADCLSR)

•

Address 0x33h - Digital Current for self-test (Medium Level) (ADCMSR)

•

Address 0x34h - Digital Current for self-test (High Level) (ADCHSR)

The microcontroller validates the expected conversions in the fail-safe state before activating the channels.

During ADC BIST execution the channels are released and could be switched on, even if no output current

sampling is executed through the ADC.

A R&C command should be sent to these registers to check for any stuck bit.

Configuration <1, 1> (default one) will end the BIST procedure by redirecting the multiplexer output current to the

IVFRAME. It is kept until the next power on reset.

Table 45. ADC BIST conversion results

Symbol

Parameter

Test conditions

Min.

Typ.

Max.

Unit

IBIST_Low

IBIST low conversion result

ADC BIST at POR;

VCC =13 V;

-12%

12%

IBIST_Mid

IBIST mid conversion result

ADC BIST at POR;

VCC =13 V;

-10%

325

10%

IBIST_High

IBIST high conversion result

ADC BIST at POR;

VCC =13 V;

-8%

890

ADC_bistexec

ADC BIST execution time

ADC BIST at POR;

VCC =13 V;

100

μs

I2t_bistexec

I²t BIST execution time (channels off)

μs

VNF9Q20F

Safety-related functions

DS13909 - Rev 6

page 70/109

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