2. State-of-the-Art Current Sensing, Biasing Schemes and Voltage References

Current regulation circuit is essential for the squib drivers to inflate airbags. Energy less than 8 mJ should be provided to the FETs to deploy the airbag. These are applicable when the driver is powered and the ACU microprocessor commands to deploy the squibs. The HS_FET is needed to provide a precise regulated current of 1.95 A (1.75 A < I _{deploy_HI} < 2.14 A) for 0.5/0.7 ms and 1.35 A (1.2 A < I _{deploy_LO} < 1.47 A) for 2 ms. The LS_FET has a current limitation of 3 A ±15%. Based on which setting is used, i.e. either I _{deploy_HI} or I _{deploy_LO}, the duration of the current limit on the LS_FET is set for a short-to-battery condition on the drain of the LS_FET. In the unpowered or partly powered (missing supplies) scenarios, the airbag misfire should not occur, and hence additional protection is needed. However, as will be discussed in this chapter, the realization of a current regulation loop and a current limitation in unpowered state, biasing scheme, diagnostic circuits exploiting voltage and current selector circuits is not currently available and is therefore the objective of the present research.