Analog Power Sequencing

Simplified Power Sequencing (XAPP1375)

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1.1 English

Analog power sequencers can be used to control the power-up and power-down of VRMs. This method usually includes comparators, state machines, and control circuitry that are used for power-on and power-off sequencing that is settable by resistor and capacitor combinations, and supports the cascading of multiple devices. For instance, a 4-channel sequencer can be cascaded with another 4-channel sequencer to make an 8-channel sequencer.

Some parameters to consider before choosing an analog power sequencer is the accuracy of the comparators and delays, and the number of channels and fault pins (if included). The analog power sequencer has fewer features compared to a digital power sequencer. The primary benefits of using an analog sequencer are its small size, low cost, and low complexity. An example of an analog sequencer is the LM388X series from Texas Instruments, as shown in the following figure. For a full list of power sequencers offered by Texas Instruments, see Sequencers.

Figure 1. Texas Instruments LM388X Analog Sequencer