SFFS311 October 2021 LMR51420 , LMR51430

4 Pin Failure Mode Analysis (Pin FMA)

This section provides a Failure Mode Analysis (FMA) for the pins of the LMR51420 and LMR51430. The failure modes covered in this document include the typical pin-by-pin failure scenarios:

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

Table 4-2 through Table 4-5 also indicate how these pin conditions can affect the device as per the failure effects classification in Table 4-1.

Table 4-1 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 4-1 shows the LMR51420 and LMR51430 pin diagram. For a detailed description of the device pins please refer to the 'Pin Configuration and Functions' section in the LMR51420 and LMR51430 datasheet.

Figure 4-1 Pin Diagram

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

Application circuit, as per the LMR51430 data sheet is used.

Table 4-2 Pin FMA for Device Pins Short-Circuited to Ground

Pin Name	Pin No	Description of Potential Failure Effect(s)	Failure Effect Class
GND	1	Normal operation	D
SW	2	Damage to HS FET	A
VIN	3	VOUT = 0 V	B
FB	4	VOUT >> than programmed output voltage	B
EN	5	VOUT = 0 V	B
CB	6	VOUT = 0 V	B

Table 4-3 Pin FMA for Device Pins Open-Circuited

Pin Name	Pin No	Description of Potential Failure Effect(s)	Failure Effect Class
GND	1	VOUT can be abnormal due to switching noise on analog circuits.	B
SW	2	VOUT = 0 V	B
VIN	3	Device can shut off	B
FB	4	VOUT >> than programmed output voltage	B
EN	5	Device can shut off	B
CB	6	VOUT = 0 V	B

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

Pin Name	Pin No	Description of Potential Failure Effect(s)	Failure Effect Class
GND	SW	Damage to HS FET	A
SW	VIN	Damage to LS FET	A
CB	EN	EN pin ESD Damage if VIN > 31 V	A
EN	FB	EN voltage lower than 5.5 V, VOUT = 0 V	B
EN	FB	EN higher than 5.5 V, damage to FB	A

Table 4-5 Pin FMA for Device Pins Short-Circuited to supply

Pin Name	Pin No	Description of Potential Failure Effect(s)	Failure Effect Class
GND	1	VOUT = 0 V. Damage to other pins referred to GND	A
SW	2	Damage to LS FET	A
VIN	3	Normal mode	D
FB	4	If VIN exceeds 5.5 V damage will occur, VOUT = 0 V.	A
EN	5	Device enabled	D
CB	6	VOUT = 0 V. CBOOT ESD clamp will run current to destruction.	A