TPS629xx-Q1 Functional Safety FIT Rate and Pin FMA

1 Overview

This document contains information for the TPS629xx-Q1 (VQFN 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
Pin failure mode analysis (Pin FMA)

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

Figure 1-1 Functional Block Diagram

The TPS629xx-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 TPS629xx-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)
Power Dissipation	0.5 W	1.0 W	1.5 W
Total Component FIT Rate	12	26	59
Die FIT Rate	8	22	55
Package FIT Rate	4	4	4

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: Automotive Control
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 29500-2T

Table	Category	Reference FIT Rate	Reference Virtual T_j
5	CMOS, BICMOS Digital, analog/mixed	25 FIT	55°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 infromation in SN 29500-2 section 4.

3 Pin Failure Mode Analysis (Pin FMA)

This section provides a Failure Mode Analysis (FMA) for the pins of the TPS629xx-Q1. The failure modes covered in this document include the typical pin-by-pin failure scenarios:

Pin short-circuited to Ground (see Table 3-2)
Pin open-circuited (see Table 3-3)
Pin short-circuited to an adjacent pin (see Table 3-4)
Pin short-circuited to VIN (see Table 3-5)

Table 3-2 through Table 3-5 also indicate how these pin conditions can affect the device as per the failure effects classification in Table 3-1.

Table 3-1 TI Classification of Failure Effects

Class	Failure Effects
A	Potential device damage that affects functionality
B	No device damage, but loss of functionality
C	No device damage, but performance degradation
D	No device damage, no impact to functionality or performance

Figure 3-1 shows the TPS629xx-Q1 pin diagram. For a detailed description of the device pins please refer to the 'Pin Configuration and Functions' section in the TPS629xx-Q1 datasheet.

Figure 3-1 PIin Diagram

Following are the assumptions of use and the device configuration assumed for the pin FMA in this section:

The device is operating in one of the two typical application configurations show in Figure 3-2 or Figure 3-3.

Figure 3-2 Adjustable V_O Operation Schematic

Figure 3-3 Selectable V_O Operation Schematic

Table 3-2 Pin FMA for Device Pins Short-Circuited to Ground

Pin Name	Pin No.	Application Configuration	Description of Potential Failure Effect(s)	Failure Effect Class
PG	1		Loss of PG functionality	C
SW	2		Possible device damage	A
VOS	3		Loss of output voltage	B
GND	4		Intended pin connection	D
EN	5		The device does not power on.	B
VIN	6		The device does not power on.	B
MODE/S-CONF	7	External FB⁽³⁾	The device runs in 2.5M-Hz APFM with AEE mode.⁽⁵⁾	C⁽⁵⁾
MODE/S-CONF	7	Internal FB⁽⁴⁾	Loss of output voltage regulation. Output voltage goes to V_IN.⁽⁵⁾ Possible device damage. ⁽²⁾ Absolute maximum voltage may be exceeded.	A⁽⁵⁾
SS/TR	8		The device does not power on.	B
FB/VSET	9	External FB⁽³⁾	Loss of output voltage regulation. Output voltage goes to V_IN. Possible device damage. ⁽²⁾Absolute maximum voltage may be exceeded.	A
FB/VSET	9	Internal FB⁽⁴⁾	The device regulates output voltage to 1.2 V.	D

Table 3-3 Pin FMA for Device Pins Open-Circuited

Pin Name	Pin No.	Application Configuration	Description of Potential Failure Effect(s)	Failure Effect Class
PG	1		Loss of PG functionality	C
SW	2		Loss of output voltage regulation	B
VOS	3	External FB⁽³⁾	Open loop operation. Undetermined output voltage behavior	B
VOS	3	Internal FB⁽⁴⁾	Loss of output voltage regulation. Output voltage may go to V_IN. Possible device damage. ⁽²⁾ Absolute maximum voltage may be exceeded.	A
GND	4		Potential device damage	A
EN	5		The device does not power on.	B
VIN	6		The device does not power on.	B
MODE/S-CONF	7	External FB⁽³⁾	The device runs in 2.5-MHz APFM with AEE mode⁽⁵⁾. Output voltage is not set based on the external resistor divider ratio. Instead, V_OUT is set according to the internal FB (VSET) table based on external feedback resistance values.	B⁽⁵⁾
MODE/S-CONF	7	Internal FB⁽⁴⁾	The device runs in 2.5-MHz APFM with AEE mode.⁽⁵⁾	C⁽⁵⁾
SS/TR	8		Allowable pin condition. Soft-start time is minimized.	D
FB/VSET	9	External FB⁽³⁾	Loss of output voltage regulation. Output voltage may go to V_IN. Possible device damage. ⁽²⁾ Absolute maximum voltage may be exceeded.	A
FB/VSET	9	Internal FB⁽⁴⁾	The device regulates output voltage to 3.3 V.	D

Table 3-4 Pin FMA for Device Pins Short-Circuited to Adjacent Pin

Pin Name	Pin No.	Shorted to	Application Configuration	Description of Potential Failure Effect(s)	Failure Effect Class
PG	1	SW		Loss of output voltage regulation and possible device damage.⁽¹⁾ Absolute maximum voltage may be exceeded if PG is connected to VOS through a resistor.	A
SW	2	VOS		Loss of output voltage regulation. Possible device damage.⁽¹⁾ Absolute maximum voltage may be exceeded.	A
VOS	3	GND		Loss of output voltage	B
GND	4	EN		The device does not power on.	B
EN	5	VIN		The device cannot be disabled.	B
VIN	6	MODE/S_CONF	External FB⁽³⁾	The device runs in 2.5-MHz FPFM mode.	C
VIN	6	MODE/S_CONF	Internal FB⁽⁴⁾	Loss of output voltage regulation. Output voltage goes to V_IN.⁽⁵⁾ Possible device damage. ⁽²⁾ Absolute maximum voltage may be exceeded.	A
MODE/S_CONF	7	SS/TR	External FB⁽³⁾	The device operating mode is indeterminate. ⁽⁵⁾	B⁽⁵⁾
MODE/S_CONF	7	SS/TR	Internal FB⁽⁴⁾	Loss of output voltage regulation. Possible device damage.⁽¹⁾ Absolute maximum voltage may be exceeded.	A
SS/TR	8	FB/VSET		Output voltage is regulated below the target value.	B
FB/VSET	9	PG		Loss of output voltage regulation. Possible device damage.⁽¹⁾ Absolute maximum voltage may be exceeded if PG is connected to VIN through a resistor.	A

Table 3-5 Pin FMA for Device Pins Short-Circuited to VIN

Pin Name	Pin No.	Application Configuration	Description of Potential Failure Effect(s)	Failure Effect Class
PG	1		Potential device damage. Absolute maximum current rating for the pin.	A
SW	2		Possible device damage. ⁽²⁾ Absolute maximum voltage may be exceeded.	A
VOS	3		Possible device damage.⁽¹⁾ Absolute maximum voltage may be exceeded.	A
GND	4		The device is not functional.	B
EN	5		The device cannot be disabled.	B
VIN	6		Intended pin connection	D
MODE/S-CONF	7	External FB⁽³⁾	The device runs in 2.5-MHz FPFM mode. ⁽⁵⁾	C⁽⁵⁾
MODE/S-CONF	7	Internal FB⁽⁴⁾	Loss of output voltage regulation. Output voltage goes to V_IN.⁽⁵⁾ Possible device damage. ⁽²⁾ Absolute maximum voltage may be exceeded.	A⁽⁵⁾
SS/TR	8		Potential device damage. Absolute maximum current rating for pin	A
FB/VSET	9		Possible device damage.⁽¹⁾ Absolute maximum voltage may be exceeded.	A

(1) Damage occurs if V_IN is greater than the 6-V absolute maximum rating for the pin.

(2) Damage occurs if V_IN is greater than the 6-V absolute maximum rating for the VOS pin.

(3) Applies to a typical application schematic as shown in Figure 3-2

(4) Applies to a typical application schematic as shown in Figure 3-3

(5) Assumes Pin FMA condition occurs prior to device being enabled. If Pin FMA condition occurs after the device is operating, the device continues operating as previously configured.

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