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A programmable after-package, on-chip reference voltage trim circuit for an integrated circuit having a plurality of programmable trim cells generating a programmed sequence. A converter is provided to convert the bit sequence into a trim current. The trim current is added to an initial value of a r

A programmable after-package, on-chip reference voltage trim circuit for an integrated circuit having a plurality of programmable trim cells generating a programmed sequence. A converter is provided to convert the bit sequence into a trim current. The trim current is added to an initial value of a reference voltage to be trimmed, as generated by the integrated circuit. Once the correct value of the trim current is determined, isolation circuitry is programmed to isolate the trim circuitry from the remainder of the IC, thereby freeing the logic and package pins associated with the IC for use by users of the IC. The preferred trim circuitry includes fuses which are blown in accordance with a bit value supplied to the trim cell to permanently fix a trim current value, once a best fit value is determined.

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1. A programmable after-package, on-chip reference voltage trim circuit for an IC, said programmable trim circuit comprising: a register being controlled to generate a sequence of test bit signal and a sequence of set bit signals; a plurality of after package programmable trim cell circuits selectiv

1. A programmable after-package, on-chip reference voltage trim circuit for an IC, said programmable trim circuit comprising: a register being controlled to generate a sequence of test bit signal and a sequence of set bit signals; a plurality of after package programmable trim cell circuits selectively coupled to said register, each said cell receiving a test bit signal and set bit signal from said register, said after package trim cells being adapted to generate an output signal equal to said test bit signal or said set bit signal, respectively, supplied to each after package trim cell; and a digital to analog converter (DAC) circuit coupled to said output signals and generating a trim current signal proportional to said output signals; a resistor to convert the trim current into a trim voltage signal, said trim voltage being added to an initial value of a reference voltage generated by said IC.