L9908 datasheet(18/152 Pages) STMICROELECTRONICS

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Functional safety

4.1

Safe states

To reach the safety requirements of the system, the following safe states are supported by L9908, with a different

associated priority level:

•

SAFE-OFF due to CLK1_TIME_OUT or NDIS=’0’. Priority Level = 1

•

SAFE-HIZ. Priority Level = 2

•

SAFE-OFF due to STD Fault detection except INT_RST or Configurable fault with related FRC set as 00.

Priority Level = 3

•

SAFE-DIS. Priority Level = 4

In case of simultaneous safe state activation requests with different safe states required, the safe state reached

by L9908 is determined by the highest priority level.

Note:

•

Priority is descending, 1 = higher priority.

•

SAFE – OFF by NDIS assertion has the highest priority all over.

4.1.1

SAFE-OFF

When SAFE-OFF is active the gate driver unit is disabled by forcing the three Half Bridges in a tristate mode so

that VGHS_n-VSHS_n = 0 V actively, VGLS_n-VSLS_n = HIZ and by disabling the Gate Drive Supply block

(CP1_EN = CP2_EN = 0).

SAFE-OFF is activated by default if the following conditions are verified:

•

STD Fault detection except INT_RST

•

CLK1_TIME_OUT

•

Configurable fault with related FRC set as 00

•

NDIS = 0

4.1.2

SAFE-DIS

When SAFE-DIS is active the gate driver unit is disabled by forcing the three Half Bridges in a tristate mode so

that VGHS_n-VSHS_n and VGLS_n-VSLSn are kept tight to 0 V actively.

SAFE-DIS is activated by default if the following conditions are verified:

•

VPRE UV fault detection

•

Configurable fault with related FRC set as 01

•

EN_BR = 0

4.1.3

SAFE-HIZ

When SAFE-HIZ is active the gate driver unit is disabled by forcing the driver output in a tristate mode so that

VGHS_n-VSHS_n and VGLS_n-VSLSn = HIZ.

SAFE-HIZ is activated by default if the following conditions are verified:

•

Fault detection which generates INT_RST

•

SW_RST

•

No STD faults present & HBn_DIS = 0 [n = 1,2,3] & STD DRV_HIZ = 1

L9908

Functional safety

DS13546 - Rev 5

page 18/152

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