L9374LF datasheet(44/80 Pages) STMICROELECTRONICS

44 / 80 page

Circuit description

L9374LF

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DocID025414 Rev 1

Figure 28. Thermal detection / protection behavior.

4.8.5

Power ground loss (PGND-loss)

PGND-loss continuously monitors the voltage between SGND and PGNDxy. If the

measured value is higher than VPG_L (Table 16) for longer than tPGND_L (Table 18) a failure

is detected. This sets the PGNDL_Qx bit (Section 5.2.2) and sets all of the set point and

control variables to zero disabling the output. There is a power ground loss bit for each

output even though Output 1 shares power ground with Output 2 and Output 3 shares

power ground with Output 4. It is not possible to switch on the output as long as the failure is

detected.

Once the power ground loss condition is removed the outputs are re-enabled by reading the

appropriate status register (SPI Status register 1 - 4). This clears the failure bit in the status

The status of the failure is shown via SPI. PGND-loss is latched and can be reset only by

accessing this register when the failure does not exist anymore.

4.8.6

Signal ground loss (SGND-loss)

The SGND-loss monitors the voltage between SGND and PGNDxy. If the measured value is

higher than VSG_L (Table 16) for tSGND_L (Table 18) a failure is detected. After this time ALL

outputs are switched off immediately and the driver is shut down. The SPI communication is

possible but there is a threshold shift at the logic output drivers due to an additional

substrate diode in the ground path between PGNDxy and SGND (see Section 5.2.1).

4.8.7

Freewheeling diode loss detection (Dx-loss)

Freewheeling diode loss is detected by measuring the current through the output clamping

structure. If the clamping structure is used for more than tDX_L(Table 18) a Dx_Loss is

detected and the appropriate Status register bit (bit D5 of status registers 1 - 4,

Section 5.2.2) is latched on. This bit can only be cleared once the failure is removed and the

status register is read.

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