TUSB4020BI-Q1
Functional Safety FIT Rate, FMD and Pin FMA

Trademarks

All trademarks are the property of their respective owners.

1 Overview

This document contains information for the TUSB4020BI-Q1 (HTQFP package) to aid in a functional safety system design. Information provided are:

Functional safety failure in time (FIT) rates of the semiconductor component estimated by the application of industry reliability standards
Component failure modes and their distribution (FMD) based on the primary function of the device
Pin failure mode analysis (pin FMA)

Figure 1-1 shows the device functional block diagram for reference.

Figure 1-1 Functional Block Diagram

The TUSB4020BI-Q1 was developed using a quality-managed development process, but was not developed in accordance with the IEC 61508 or ISO 26262 standards.

2 Functional Safety Failure In Time (FIT) Rates

This section provides functional safety failure in time (FIT) rates for the TUSB4020BI-Q1 based on two different industry-wide used reliability standards:

Table 2-1 provides FIT rates based on IEC TR 62380 / ISO 26262 part 11
Table 2-2 provides FIT rates based on the Siemens Norm SN 29500-2

Table 2-1 Component Failure Rates per IEC TR 62380 / ISO 26262 Part 11

FIT IEC TR 62380 / ISO 26262	FIT (Failures Per 10⁹ Hours)
Total component FIT rate	35
Die FIT rate	3
Package FIT rate	32

The failure rate and mission profile information in Table 2-1 comes from the reliability data handbook IEC TR 62380 / ISO 26262 part 11:

Mission profile: Passenger compartment from table 11
Power dissipation: 345 mW
Climate type: World-wide table 8
Package factor (lambda 3): Table 17b
Substrate material: FR4
EOS FIT rate assumed: 0 FIT

Table 2-2 Component Failure Rates per Siemens Norm SN 29500-2

Table	Category	Reference FIT Rate	Reference Virtual T_J
5	CMOS, BICMOS Digital, analog, or mixed ≤ 50V supply	70 FIT	70°C

The reference FIT rate and reference virtual T_J (junction temperature) in Table 2-2 come from the Siemens Norm SN 29500-2 tables 1 through 5. Failure rates under operating conditions are calculated from the reference failure rate and virtual junction temperature using conversion information in SN 29500-2 section 4.

3 Failure Mode Distribution (FMD)

The failure mode distribution estimation for the TUSB4020BI-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 resulting from misuse or overstress.

Table 3-1 Die Failure Modes and Distribution

Outputs of the TUSB4020BI-Q1	Function	Die Failure Modes	Failure Mode Distribution (%)
USB2 Upstream	Communication	Upstream communication error	18
USB Downstream 1	Communication	Downstream 1 communication error	18
USB Downstream 2	Communication	Downstream 2 communication error	18
Both USB Downstream 1 and 2	Communication	Both downstream 1 and 2 communication error	2
USB Downstream 1	Charging control	Downstream 1 charging error	14
USB Downstream 2	Charging control	Downstream 2 charging error	14
Both USB Downstream 1 and 2	Charging control	Both downstream 1 and 2 charging error	2
I²C/SMBus	Communication	I²C/SMBus control communication error	14