Apparatus and method for power sequencing for a power management unit

Abstract

A PMU that includes LDOs is provided. The PMU also includes, for each LDO, a corresponding reference circuit that provides a reference voltage for the LDO. Further, the PMU includes a central bias circuit that provides a reference current to each of the voltage reference circuits. Each reference circuit includes a delay circuit, a counter, a binary-weighted resistor ladder, and switches coupled to the resistor ladder. In each reference circuit, the resistor ladder provides the corresponding reference voltage from the received reference current. Further, the counter controls the switches to 'step up' the reference voltage in a well-defined manner during the power-up sequence. The reference voltage is stepped up from a minimum voltage to a final reference voltage by one least significant bit at each clock pulse. Also, the delay circuits are employed to control when each reference voltage begins to increase from the minimum voltage.