L9374LF datasheet(48/80 Pages) STMICROELECTRONICS

48 / 80 page

Circuit description

L9374LF

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DocID025414 Rev 1

4.8.12

ALU- BIST (Build in self test)

The ALU BIST is based on a Cyclic Redundancy Check (CRC) value calculation. For this

reason it is possible to bring the sequencer, which controls the calculation of the current

regulation ALU, into a special BIST mode. This mode is programmable via SPI using a

special sequence of commands. The BIST is enabled when the fast switch off (FSOFF_ALL

= ‘10’) command is given. The BIST then starts when the Res_CCV command (Res_CCV =

‘01’) along with a characteristic polynomial is programmed via SPI into register 15 (see

Section 5.1.9). The BIST is autonomous, once it is started, it cannot be interrupted. The

internal registers are used to provide values to the ALU during the BIST. These registers will

be reset at the start of the BIST. After the BIST has finished the BIST busy bit (status

address 5, bit D9) is reset and the CRC checksum is available. The checksum and can be

read out via SPI from the ISAT_Q3 register (status address 8, bits D0 - D9, Section 5.2.5).

The BIST mode can then be exited when the fast switch off all command is reversed

(FSOFF_ALL = ‘01’). The used registers will be cleared to their power-on reset state when

the L9374LF exits BIST mode.

Figure 29. Functional overview of the ALU BIST

To achieve test coverage higher than 97% with the BIST the following 4 polynomial values

are recommended.

194d (1100 0010)

225d (1110 0001)

212d (1101 0100)

245d (1111 0101)

Sequence to perform the ALU built in self test during application:

Initiate the BIST sequencer; SPI command address: 2, FSOFF_ALL = 10).

Note: The sequencer is then waiting for the programming of the characteristic

polynomial to start the BIST.

Program the characteristic polynomial (SPI command address 15 RL= xxxxxxxx) while

setting Res_CCV (=’01’). While the BIST is running BIST busy bit (BIST_BUSY Status

address 5, bit D9) is set to ‘1’.

Note: Programming address 15 starts the BIST sequence. At the beginning of the

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