L9969X datasheet(36/70 Pages) STMICROELECTRONICS

36 / 70 page

Figure 23. Principle of the short circuit across load detection (OVC on HS2 when PWM = 1)

Device enabled and working: HS2 and LS1 are ON

OVC occurs on HS2

HS2 is immediately turned OFF (t_DF_off)

LS1 is turned OFF too after t_DF_del

Drivers are turned ON again after t_retest

OVC occurs on HS2?

HS2 is immediately turned OFF (t_DF_off)

LS1 is turned OFF too after t_DF_del

HS2 Driver is turned ON again after t_SC

With LS1 OFF

OVC occurs on HS2?

HS2 is immediately turned OFF (t_DF_off)

SCG is asserted on DIA1_REG

SCL is asserted on DIA1_REG

YES

Attempt to restart

Short discrimination

3.2.6.7

Short Circuit detection and behavior afterwards

•

After a detected short circuit (SCG, SCB or SCL) both outputs are switched to tri-state.

•

If only one output has diagnosed a short circuit, the second output is switched off after a delay time tDF_del .

This delay time allows the free-wheeling of the inductive energy stored in the load.

•

If a short circuit is detected on both outputs, they are both switched off immediately. If the second short

circuit is detected during tDF_del, the second output is switched off immediately too.

Anytime a SCB or a SCG is detected, L9969 allows to distinguish if there is only a single SC or a SCL. Therefore

a sequence starts running internally after the detected fault SCB or SCG. This sequence of confirmation is short

enough to prevent any mechanical reaction in the connected load.

This is checked internally by switching the second half-bridge to GND and the first half-bridge to GND too, by

releasing the power-stage for a short period tretest. If now the SCB on OUT1 disappears, one has a SCL,

otherwise the SCB on OUT1 is detected correctly. This testing is different from the normal operation, where only

one diagonal path is switched.

Theoretically, there could be the following failure scenario: as DIRx=0 and PWMx=0, a short to battery on OUTx1

occurs, consequently a short to battery detection on OUTx1 LS eventually leads to both OUTx1 LS and OUTx2

LS drivers turn-OFF after filter-time; t_RETEST timer starts. During t_RETEST counting, the short condition

changes from short to battery on OUTx1 to short to ground on OUTx1; as t_RETEST counting expires, both

OUTx1 LS and OUTx2 LS drivers are re-enabled and the previous fault detection is not confirmed and bridge

actuation control returns to the PWMx pin. As PWMx pin status changes back from 0 to 1, OUTx1 HS driver is

enabled as requested; by the way, short to ground on OUTx1 is present, thus both OUTx1 HS and OUTx2 LS

drivers are turned-OFF after filter-time: as no further scenario change occurs, the short confirmation procedure is

completed, confirming the short to ground on OUTx1.

3.2.6.8

Undervoltage shutdown

In case of undervoltage on VS, L9969 reacts by shutting down. The diagnosis of VS undervoltage is also available

on SPI registers; in fact undervoltage on VS does not reset the SPI interface. The involved parameters in

undervoltage shutdown are reported in Table 22.

L9969x

Functional description

DS14029 - Rev 6

page 36/70

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