L9788 datasheet(120/264 Pages) STMICROELECTRONICS

120 / 264 page

High/low-side drivers - STARTER STR[1:3]

L9788

120/264

DS12308 Rev 4

8.6

Starter control

To prevent unintended activation of starter relays at the same time a dual control

mechanism is implemented inside the logic by means of independent MSC commands for

on/off for each starter (RLY4_ON RLY4_OFF STR2_ON STR2_OFF STR3_ON

STR3_OFF). If the RLY4, STR2, STR3 are not configured as starter they are controlled by

data frame on/off as the other drivers

The starter control function comes with a dedicated failsafe management circuit to always

provide a safety switch off path able to disconnect the main supply in case of fault

conditions. Starter switch off path is implemented with dual polarity command acting on

drivers STR[2:3] and RLY4: if the EN_P pin is high or the EN_N pin is high or if the

FAULT_WARN is activated. RLY4, STR2, STR3 are switched off by the safety switched off

path independently if they are configured as starter.

Safety switch off path can be triggered both by the micro-controller through EN pins or by

the L9788 detection of an internal fault as described in the Figure 47.

The functionality of the switch off path is guaranteed through physical isolation from the rest

of the device: the circuit is kept layouted in a dedicated area surrounded by trench

isolations, avoiding top routing over this cell and keeping a safe distance respect to the

nearby functional top routing to ensure complete independency.

The switch off path generates locally its supply voltage to drive the safety turn-off switch in

order to avoid interactions with the rest of the L9788; the supply voltage is created starting

directly from battery line. All the circuits used inside the switch-off path are able to sustain

high voltage to prevent unwanted functionality in case of local failure, moreover no external

reference is routed to this area and the EN_N and EN_P control logic is located inside this

area as well to complete isolation and remove any dependency from the rest of the L9788.

L9788 Datasheet(PDF) 120 Page - STMicroelectronics