Power-on

Notes

Excessive supply current at power-on is the classic early sign of a short, a floating input or a reset sequencing error.

Overview

Power-on is the first application of power to new silicon or a new board, and in silicon bring-up it marks the formal start of work on the real part. Engineers bring the supplies up in a controlled way and check rail voltages, current draw, clocks and reset behaviour before attempting anything more ambitious. The same word also describes every routine start-up of a finished product, which on the chip is handled by a power-on reset circuit.

How it works

A first power-on, often called a smoke test or power-on test in electronics generally, is the moment design or assembly mistakes show themselves. Engineers commonly raise the supply gradually while watching the current, because a short circuit, a reversed part or a wrong component shows up as excess current or heat long before anything works. Each rail is then measured against its target before the next step.

Processors, FPGAs, ASICs and microcontrollers usually need several supplies for the core, memory and I/O, and many of them require those rails to rise and fall in a specific order for reliable operation. Boards therefore use sequencers, from simple analogue parts to programmable digital controllers, together with voltage supervisors that monitor the rails and hold reset until they are valid. Getting the order or timing wrong can prevent a reliable start.

Inside the chip, a power-on reset circuit holds the logic in reset as the supply rises, so that the device starts in a known state rather than wherever its flip-flops happened to settle. A simple version uses a resistor and capacitor with a Schmitt trigger; a very slow supply ramp can defeat it, releasing reset too early. Modern chips also generate many other resets on chip for power management and debug, so the power-on reset is only the first of several. Once reset is released, engineers confirm that clocks start and that the first boot code runs before moving on to wider testing.

Examples

• The first power-on of a new SoC on an evaluation board, with each rail raised in turn from a current-limited supply and its current logged.
• A digital sequencer from Texas Instruments' UCD90 family bringing up core, memory and I/O rails in the order a processor requires.
• A slowly ramping supply that lets an RC-based power-on reset release too early, leaving the chip in an unknown state.
• A smoke test on a hand-built prototype board where excess current reveals a part fitted the wrong way round.

Why it matters

First power-on is a schedule milestone and a risk point: a fault found here can cost a board, a sample or weeks of investigation. Silicon and board bring-up engineers, lab technicians, hardware designers and power management designers all prepare for it with checklists, current-limited supplies and agreed sequences.

In the chip lifecycle, the power and reset strategy is set at architecture, power-up behaviour is checked in power-aware simulation, the first power-on happens when samples arrive after tapeout, and every later start-up in qualification, production test and the field repeats the same sequence.

It matters most to: Board Bring-up Engineer, Hardware Bring-Up Technician, Post-Silicon Validation Engineer, Power Management IC Design Engineer, Silicon Bring-up Engineer

Common confusions

Not the same as power-on reset (POR)

A power-on reset is the circuit that produces a reset each time power is applied. Power-on in bring-up is the event and milestone of first powering a new part.

Not the same as power-on self-test (POST)

POST is a set of diagnostic checks that firmware runs at each start-up of a computer. It happens after power-on, once the processor is already executing code.

Sources

1. Sequencers (opens in a new tab), Texas Instruments, 2026-10-22
2. Supervisor and reset ICs (opens in a new tab), Texas Instruments, 2026-10-22
3. What is Reset Domain Crossing? ASIC Design Challenges (Paras Mal Jain and Rimpy Chugh, 7 February 2022) (opens in a new tab), Synopsys, 2026-10-22
4. Power-on reset (Wikipedia) (opens in a new tab), Wikimedia Foundation, 2026-10-22
5. Smoke testing (electrical) (Wikipedia) (opens in a new tab), Wikimedia Foundation, 2026-10-22

Related terms

• Smoke test
• First silicon
• Rail
• Silicon debug

Where it appears on the Hub

Used on 13 pages of the Hub. In each group, the pages that mention it most come first.