SFFS347 December 2021 LM25149

4 Pin Failure Mode Analysis (Pin FMA)

This section provides a Failure Mode Analysis (FMA) for the pins of the LM25149. 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 LM25149 pin diagram. For a detailed description of the device pins please refer to the Pin Configuration and Functions section in the LM25149 data sheet.

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 LM25149 data sheet is used
- PG is pulled up to VOUT

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
AVSS	1	AVSS is ground. V_OUT = expected V_OUT	D
INJ	2	Active EMI filtering will not work but the regulator will continue regulating. V_OUT = expected V_OUT	C
CNFG	3	Active EMI filtering will be disabled. V_OUT is unaffected.	C
RT	4	V_OUT will attempt to regulate at maximum f_SW, causing maximum power dissipation.	B
EXTCOMP	5	V_OUT = 0 V	B
FB	6	Internal FB mode, V_OUT = expected V_OUT	D
FB	6	External FB mode, V_OUT = V_IN	A
AGND	7	AGND is GND. V_OUT = expected V_OUT	D
VDDA	8	V_OUT = 0 V, no switching, loaded VCC output	B
VCC	9	V_OUT = 0 V, no switching, loaded VCC output	B
PGND	10	PGND is GND. V_OUT = expected V_OUT	D
LO	11	V_OUT = 0 V, VCC regulator loaded to the current limit	B
VIN	12	V_OUT = 0 V	B
HO	13	V_OUT = 0 V, VCC regulator loaded to the current limit	B
SW	14	V_OUT = 0 V. High-side FET is shorted from VIN to GND.	A
CBOOT	15	V_OUT = 0, VCC regulator loaded to the current limit	B
VCCX	16	V_OUT = expected V_OUT. The internal VCC regulator provides bias voltage.	C
PG	17	If in single phase, PG has no effect on operation. V_OUT = expected V_OUT	C
PG	17	If in interleaved primary mode, the secondary will detect no clock input and will shut down. Secondary phase is disabled and primary phase can current limit.	B
PFM/SYNC	18	V_OUT = expected V_OUT. No synchronization will be available and the LM25149 will be in FPWM mode.	C
EN	19	V_OUT = 0 V. The LM25149 enters shutdown.	C
ISNS+	20	V_OUT = 0 V; HO damaged	A
VOUT	21	V_OUT = 0 V. Current limit reached and hiccup mode occurs.	B
AEFVDDA	22	AEFVDDA = VCC. VCC is shorted and V_OUT = 0 V. VCC is loaded.	B
SEN	23	Active EMI filtering will not work but the regulator will continue regulating. V_OUT = expected V_OUT	B
REFAGND	24	REFAGND is ground. V_OUT = expected V_OUT	D

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

Pin Name	Pin No.	Description of Potential Failure Effect(s)	Failure Effect Class
AVSS	1	Active EMI filtering will not work but the regulator will continue regulating. V_OUT = expected V_OUT	C
INJ	2	Active EMI filtering will not work but the regulator will continue regulating. V_OUT = expected V_OUT	C
CNFG	3	V_OUT will continue operating normally. CNFG is used during start-up and enables AEF.	C
RT	4	RT will regulate to 500 mV, but the internal oscillator will not function.	B
EXTCOMP	5	V_OUT will oscillate. If V_OUT oscillates to V_IN, damage can occur if V_IN > 60 V.	A
FB	6	Internal FB mode, V_OUT = expected V_OUT	D
FB	6	External FB mode, V_OUT = V_IN	A
AGND	7	V_OUT is indeterminate.	B
VDDA	8	Poor noise immunity	C
VCC	9	V_OUT = 0 V	B
PGND	10	V_OUT = 0 V	B
LO	11	V_OUT = expected V_OUT with reduced efficiency	C
VIN	12	V_OUT = 0 V	C
HO	13	If HO is opened while HO to SW has voltage, the high-side FET will never turn off. V_OUT = V_IN	A
SW	14	V_OUT is indeterminate. The CBOOT floating rail has no reference to the actual SW node. V_OUT = V_IN	A
CBOOT	15	V_OUT = 0 V	B
VCCX	16	VCCX is held to ground by a weak pulldown. V_OUT = expected V_OUT	D
PG	17	If in single phase, PG has no effect on operation. V_OUT = expected V_OUT	C
PG	17	If in interleaved primary mode, the secondary will detect no clock input and will shut down. The secondary phase is disabled and primary phase can current limit.	B
PFM/SYNC	18	V_OUT = expected V_OUT	D
EN	19	V_OUT = expected V_OUT	D
ISNS+	20	The OPEN ISNS+ pin will block current limit and cause V_OUT oscillations.	A
VOUT	21	V_OUT = 0 V	B
AEFVDDA	22	Active EMI filtering will not function.	C
SEN	23	Active EMI filtering will not function.	C
REFAGND	24	Active EMI filtering will not function.	C

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

Pin Name	Pin No.	Shorted to	Description of Potential Failure Effect(s)	Failure Effect Class
AVSS	1	INJ	Active EMI filtering will not function. VOUT = expected V_OUT	C
INJ	2	CNFG	Active EMI filtering will not function. VOUT = expected V_OUT	C
CNFG	3	RT	V_OUT = expected V_OUT with erratic switching	B
RT	4	EXTCOMP	COMP cannot regulate down due to clamping by the internal RT.	B
EXTCOMP	5	FB	External FB mode: COMP will regulate to .8 V and the output will be unregulated. V_OUT = any voltage	B
EXTCOMP	5	FB	Internal FB mode: COMP will rise up to VDD. V_OUT = V_IN	A
FB	6	AGND	External FB mode: V_OUT = V_IN	A
FB	6	AGND	Internal FB mode: V_OUT = expected V_OUT	D
AGND	7	VDDA	VDDA will be grounded. V_OUT = 0 V	B
VDDA	8	VCC	V_OUT = expected V_OUT	D
VCC	9	PGND	VCC will be grounded. V_OUT = 0 V	B
PGND	10	LO	V_OUT = 0 V. VCC is loaded by LO driver.	B
LO	11	VIN	V_OUT = 0 V. The driver will be damaged if V_IN > 6.5 V.	A
VIN	12	HO	V_OUT = V_IN	A
HO	13	SW	V_OUT = 0 V	B
SW	14	CBOOT	V_OUT = 0 V	B
CBOOT	15	VCCX	V_OUT < 5 V	A
VCCX	16	PG	PG pulldown can damage. V_OUT = expected V_OUT	A
PG	17	PFM/SYNC	V_OUT = expected V_OUT	C
PFM/SYNC	18	EN	V_OUT = expected V_OUT	A
EN	19	ISNS+	EN is high voltage rated. V_OUT = expected V_OUT if V_OUT > 1 V. If V_OUT < 1 V, the device is disabled.	B
ISNS+	20	VOUT	Current limit is disabled since the current limit resistor would be shorted. V_OUT cannot regulate since current mode feedback is shorted.	A
VOUT	21	AEFVDDA	Active EMI filtering will not function and damage will occur if V_OUT > 6.5 V. V_OUT = expected V_OUT	A
AEFVDDA	22	SEN	Active EMI filtering will not function. V_OUT = expected V_OUT	C
SEN	23	REFAGND	Active EMI filtering will not function. V_OUT = expected V_OUT	C
REFAGND	24	AVSS	No impact	D

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

Pin Name	Pin No.	Description of Potential Failure Effect(s)	Failure Effect Class
AVSS	1	Active EMI filtering will not function, high V_IN current	A
INJ	2	Active EMI filtering will not function, high V_IN current	A
CNFG	3	V_OUT = V_IN	A
RT	4	V_OUT = 0 V; high V_IN current	A
EXTCOMP	5	This will bring VDDA up to V_IN. V_OUT = V_IN.	A
FB	6	This will bring VDDA up to V_IN. V_OUT = V_IN	A
AGND	7	V_OUT = V_IN; high VIN current	A
VDDA	8	If V_IN < 6.5 V, V_OUT = expected V_OUT	D
VDDA	8	If V_IN > 6.5 V, exceeds maximum ratings and VDDA is damaged.	A
VCC	9	If V_IN < 6.5 V, V_OUT = expected V_OUT	D
VCC	9	If V_IN > 6.5 V, exceeds maximum ratings and VCC is damaged.	A
PGND	10	V_OUT = VIN; high V_IN current	A
LO	11	For V_IN < 6.5 V, V_OUT = 0; excess current from V_IN	B
LO	11	For V_IN > 6.5 V, exceeds maximum ratings and pin LO is damaged.	A
VIN	12	N/A	D
HO	13	For V_IN < 6.5 V, V_OUT = dropout lower than V_IN, no switching, excess current from V_IN	B
HO	13	For V_IN > 6.5 V, exceeds maximum ratings and HO is damaged, V_OUT = V_IN	A
SW	14	V_OUT = V_IN, excess current from V_IN. LO turns on and shorts against V_IN.	A
CBOOT	15	For V_IN < 6.5 V, V_OUT = expected V_OUT, erratic switching	B
CBOOT	15	For V_IN > 6.5 V, exceeds maximum ratings and the CBOOT pin is damaged, HO damaged. V_OUT = V_IN	A
VCCX	16	If VCCX = V_OUT, for V_IN < 6.5 V, V_OUT = V_IN	B
VCCX	16	For V_IN > 6.5 V, exceeds maximum ratings and VCCX is damaged.	A
PG	17	For V_IN < 6.5 V, V_OUT = expected V_OUT, PG forced high	B
PG	17	For V_IN > 6.5 V, exceeds maximum ratings and PG is destroyed.	A
PFM/SYNC	18	If PFM = GND, V_OUT = 0 V, excess current from V_IN	B
		If PFM = VDDA and V_IN < 6.5 V, V_OUT = expected V_OUT and erratic switching.	B
		If V_IN > 6.5 V, exceeds maximum ratings and PFM is damaged. V_OUT = expected V_OUT	A
EN	19	The part will be always on. V_OUT = expected V_OUT	C
ISNS+	20	If V_IN < 60 V, V_OUT = V_IN	B
ISNS+	20	If V_IN > 60 V, exceeds maximum ratings and CS is damaged.	A
VOUT	21	If V_IN < 60 V, V_OUT = V_IN	B
VOUT	21	If V_IN > 60 V, exceeds maximum ratings and CS is damaged.	A
AEFVDDA	22	Active EMI filtering will not function, high V_IN current	A
SEN	23	Active EMI filtering will not function, high V_IN current	A
REFAGND	24	Active EMI filtering will not function, high V_IN current	A