TRANSIENT BLOCKING UNIT HAVING A FAB-ADJUSTABLE THRESHOLD CURRENT

摘要

A transient blocking unit (TBU) is a transistor circuit that is normally on, but rapidly and automatically switches to a high-resistance current blocking state when a current threshold is exceeded, thereby protecting a series connected load from over-voltage or over-current conditions. Process variation of transistor threshold voltage and on-resistance can cause undesirable variation of the TBU threshold current and/or of TBU resistance. Control of TBU threshold current and/or resistance is improved by providing for trimming the TBU during its fabrication to provide a one-time adjustment of the threshold current or resistance. Such trimming can be done with a resistive trimming circuit placed in series with the on- resistance of the relevant TBU transistor. Alternatively, a segmented TBU transistor having an on-resistance that is adjustable by way of wire bonding during fabrication can be employed.