L9678P datasheet(110/203 Pages) STMICROELECTRONICS

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Deployment drivers

L9678P, L9678P-S

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DocID029274 Rev 3

Deployment drivers

The squib deployment block consists of 4 independent high side drivers and 4 independent

low side drivers. Squib deployment logic requires a deploy command received through SPI

communications and either an arming condition processed by safing logic or a proper FENH

and FENL input pin assessment, depending on whether the internal safing engine is used or

not. FENH signal is used to enable high side squib drivers and is active high, while FENL

enables low side drivers and is active low. Both conditions must exist in order for the

deployment to occur. Once a deployment is initiated, it can only be terminated by a RESET

event.

L9678P allows all 4 squib loops to be deployed at the very same time or in other possible

timing sequence. Deployment drivers are capable of granting a successful deployment also

in case of short to ground on low-side circuit (SRx pins). Firing voltage capability across high

side circuit is maximum 25 V. High side and low side drivers account for a maximum series

total resistance of 2 Ω. Each loop is granted for a minimum number of deployments of 50,

under all normal operating conditions and with a deployment repetition time higher than 10s.

6.1

Control logic

A block diagram representing the deployment driver logic is shown below. Deployment

driver logic features include:



Deploy command logic



Deployment current selection



Deployment current monitoring and deploy success feedback



Diagnostic control and feedback

Figure 20. Deployment driver control blocks

L9678P Arkusz danych(PDF) 110 Page - STMicroelectronics