SFFS570 January   2025 ISOUSB211

 

  1.   1
  2.   Trademarks
  3. 1Overview
  4. 2Functional Safety Failure In Time (FIT) Rates
  5. 3Failure Mode Distribution (FMD)
  6. 4Pin Failure Mode Analysis (Pin FMA)
  7. 5Revision History

3 Failure Mode Distribution (FMD)

The failure mode distribution estimation for the ISOUSB211 (DP-28 package) 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 resulting from misuse or overstress.

Table 3-1 Die Failure Modes and Distribution
Die Failure Modes Failure Mode Distribution (%)
DD+ and DD- stuck low
DD+ or DD- stuck low		 7.5
DD+ and DD- stuck high
DD+ or DD- stuck high		 7.5
DD+ and DD- undetermined
DD+ or DD- undetermined		 20
DD+ and DD- out of electrical or timing specification
DD+ or DD- out of electrical or timing specification		 15
UD+ and UD- stuck low
UD+ or UD- stuck low		 7.5
UD+ and UD- stuck high
UD+ or UD- stuck high		 7.5
UD+ and UD- undetermined
UD+ or UD- undetermined		 20
UD+ and UD- out of electrical or timing specification
UD+ or UD- out of electrical or timing specification		 15

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

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

Apply creepage and clearance requirements according to the specific equipment isolation standards of an application. Care must 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.