SFFS070 February 2021 TPS25846-Q1

3 Failure Mode Distribution (FMD)

The failure mode distribution estimation for TPS25846-Q1 in Table 3-1 comes from the combination of common failure modes listed in standards such as IEC 61508 and ISO 26262, the ratio of sub-circuit function size and complexity and from best engineering judgment.

The failure modes listed in this section reflect random failure events and do not include failures due to misuse or overstress.

Table 3-1 Die Failure Modes and Distribution

Die Failure Modes	Failure Mode Distribution (%)
SW no output	25%
CSN/OUT not in specification – voltage or timing	20%
LS/GD no output	5%
LS/GD not in specification – voltage or timing	5%
DP_IN, DM_IN, DP_OUT, DM_OUT no output	15%
DP_IN, DM_IN, DP_OUT, DM_OUT not in specification – voltage or timing	20%
FAULT, BUCK_ST false trip or fails to trip	5%
Short circuit any two pins	5%

The FMD in Table 3-1 excludes short circuit faults across the isolation barrier. Faults for short circuit across the isolation barrier can be excluded according to ISO 61800-5-2:2016 if the following requirements are fulfilled:

The signal isolation component is OVC III according to IEC 61800-5-1. If a SELV/PELV power supply is used, pollution degree 2/OVC II applies. All requirements of IEC 61800-5-1:2007, 4.3.6 apply.
Measures are taken to ensure that an internal failure of the signal isolation component cannot result in excessive temperature of its insulating material.

Creepage and clearance requirements should be applied according to the specific equipment isolation standards of an application. Care should be taken to maintain the creepage and clearance distance of a board design to ensure that the mounting pads of the isolator on the printed-circuit board do not reduce this distance.