L9958XP datasheet(20/38 Pages) STMICROELECTRONICS

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Diagnostics and protections

L9958

20/38

Doc ID 17269 Rev 5

5.2

Protection and on state diagnostics

L9958 is protected against short circuits, overload and invalid supply voltage by the

following measures.

5.2.1

Over-current on high-side - short to ground

The high-side switches are protected against a short of the output to ground by an over-

current shutdown. If a high-side switch is turned on and the current rises above the short

circuit detection current Ioc all output transistors are turned off after a filter time Toc_ls and

the error bits "overcurrent on high side 1 (2)", OC_HS1 (OC_HS2) are stored in the internal

status register.

5.2.2

Over-current on low-side - short to Vs

Due to the chopper current regulation, the low-side switches are already protected against a

short to the supply voltage. To be able to distinguish a short circuit from normal current limit

operation, the current limitation is deactivated for the blanking time tb after the current has

exceeded the current limit threshold IH. If the short circuit detection current Ioc is reached

within this blanking time, a short circuit is detected. All output transistors are turned OFF

and the according error bit “Over-Current on Low Side 1 (2)”, OC_LS1 (OC_LS2) is set.

5.2.3

Short circuit over-load

If, during the Blanking time (tb) of the current regulation mode, the current reaches the Ioc

threshold; after a filtering time, the output MOS are switched OFF and the “Short circuit over

load” can be checked by the reading of the overcurrent bits of the DIA_REG (please refer to

Table 8 bit 8, 9,10 and 11).

Figure 15.

Diagnostics for SCB / SCOL

5.2.4

Open load in on state

To perform the Open Load diagnosis in ON state, the flag OL_ON has to be set high through

SPI. After every open load diagnosis in ON state, the OL_ON flag is resetted, to perform a

new open load diagnosis in ON state the OL_ON flag has to be set again.

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