ATX Version 3 Multi Rail Desktop Platform Power Supply

Design Guide

ID Date Version Classification
336521 11/01/2023 Public
Document Table of Contents

Timing, Housekeeping and Control – REQUIRED

Figure 4-3: Power on Timing

image6.png

Table 4-10: Power Supply Timing

Parameter

Description

Value

Legacy Timings1

Required

Recommended

T0

AC power on time

-

<2s

-

T1

Power-on time7

< 500 ms

< 200 ms

<150 ms8

T2

Rise time

-

0.2 – 20 ms

-

T3

PWR_​OK delay7

100 ms2 – 500 ms

100 ms2 – 250 ms

100 ms2 – 150 ms8

T4

PWR_​OK rise time

-

< 10 ms

-

T5

AC loss to PWR_​OK hold-up time

-

> 11 ms3

> 16 ms4

T6

PWR_​OK inactive to DC loss delay

-

> 1 ms5

> 1 ms6

  1. Value in the Legacy column list timings for power supplies designed before the year 2020. In 2020, the T1 and T3 timings have moved from the Legacy timing to the new Required column for all new power supply designs.
  2. T3 minimum time faster than 100 ms is not recommended for previous generation motherboards and systems. All design tolerances must be considered before allowing T3 faster than 100 ms.
    1. A T3 time less than 100 ms may be designed based on system requirements and a need to provide faster PSU and system turn on capability. However, PSU and system designers are highly recommended to verify and ensure no PSU and system compatibility problems exist, especially for previous generation motherboards and systems.
  3. T5 Required value to be defined for both Full/Light load conditions.
  4. T5 Recommended value is defined for 80% of full load condition.
  5. T6 Required value to be defined for coming from both Full/Light load conditions.
  6. T6 Recommended value is defined for coming from 80% of full load condition.
  7. PSUs are recommended to label or indicate the timing value for system designer and integrator reference for T1 and T3. This allows system designers to optimize “turn on” time within the system.
  8. Timing values recommended for systems that use ALPM.