4 Pin Failure Mode Analysis (Pin FMA)

This section provides a failure mode analysis (FMA) for the pins of the LM5171-Q1 and LM5171. The failure modes covered in this document include the typical pin-by-pin failure scenarios:

Pin short-circuited to ground (see Pin FMA for Device Pins Short-Circuited to Ground)
Pin open-circuited (see Pin FMA for Device Pins Open-Circuited)
Pin short-circuited to an adjacent pin (see Pin FMA for Device Pins Short-Circuited to Adjacent Pin)

Table 4-2 through Table 4-3 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.

Pin Diagram shows the LM5171-Q1/LM5171 pin diagram. For a detailed description of the device pins, see the Pin Configuration and Functions section in the LM5171-Q1/LM5171 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:

Device used within the Recommended Operation Conditions and the Absolute Maximum Ratings found in the LM5171-Q1 or LM5171 data sheet.
For the analysis, the typical application as shown in the Typical Application section of the LM5171-Q1 or LM5171 is used.
V_supply = V_cc = 10 V
V_OUT = 12 V

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

Pin No	Pin Name	Description of Potential Failure Effect (s)	Failure Effect Class
1	VREF	No switching	B
2	FBLV	No switching	B
3	ERRLV	No switching	B
4	IMON2	Normal operation, but loss of CH-2 current monitor	D
5	CSA2	Invalid current sense, and 12V Rail is shorted to GND	B
6	CSB2	Invalid current sense, and 12V Rail is shorted to GND	B
7	ISET2	Loss of current setting command in CH-2	B
8	COMP2	No switching in CH-2	B
9	SS/DEM2	No switching in CH-2	B
10	EN2	No switching in CH-2	B
11	DIR2	CH-2 can only operate in Boost Mode, no Buck Mode possible	C
12	VDD	Unable to startup	B
13	HV2	CH-2 Unable to Startup	B
14	HB2	No CH-2 high-side boot voltage; not able to run CH-2 in buck mode	B
15	HO2	CH-2 high side driver may be damaged	B
16	SW2	Switch Node of CH-2 grounded	B
17	LO2	Overloading of the CH-2 low side driver	B
18	PGND	Normal operation	D
19	VCC	Loss of VCC bias supply. Unable to start up	B
20	LO1	Overloading of the CH-1 low side driver	B
21	SW1	Switch Node of CH-1 grounded	B
22	HO1	CH-1 high side driver may be damaged	B
23	HB1	No CH-1 high-side boot voltage; not able to run CH-1 in buck mode	B
24	HV1	CH-1 Unable to Startup	B
25	LDODRV	Normal operation, but VCC pin must be supplied externally	D
26	DIR1	CH-1 can only operate in Boost Mode, no Buck Mode possible	C
27	EN1	No switching in CH-1	B
28	SS/DEM1	No switching in CH-1	B
29	COMP1	No switching in CH-1	B
30	ISET1	Loss of current setting command in CH-1	B
31	CSB1	Invalid current sense, and 12V Rail is shorted to GND	B
32	CSA1	Invalid current sense, and 12V Rail is shorted to GND	B
33	IMON1	Normal operation, but loss of CH-1 current monitor	D
34	EERHV	No switching	B
35	FBHV	No switching	B
36	OVP	Normal operation. Loss of 48V OVP in CH-1 or both channels in parallel operation	D
37	SDA	Normal operation but no I2C communication	D
38	SCL	Normal operation but no I2C communication	D
39	SYNCO	Normal operation, loss of synchronization for responder phases	D
40	SYNCI	Normal operation, loss of synchronization	D
41	OPT	Normal operation, loss of synchronization	D
42	OSC	Clock frequency is higher, unpredictable switching behavior	B
43	AGND	Normal operation	D
44	CFG	Normal operation, but current monitor only possible for Boost mode for single I2C address	D
45	UVLO	Unable to startup	B
46	DT/SD	Unable to startup	B
47	IPK	No switching	B
48	VSET	No switching	B

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

Pin No	Pin Name	Description of Potential Failure Effect (s)	Failure Effect Class
1	VREF	No switching	B
2	FBLV	No switching	B
3	ERRLV	No switching	B
4	IMON2	Normal operation, but loss of CH-2 current monitor	D
5	CSA2	Loss of CH-2 current regulation	B
6	CSB2	Loss of CH-2 current regulation	B
7	ISET2	Loss of current setting command in CH-2	B
8	COMP2	Loss of CH-2 loop compensation and loss of loop stability	B
9	SS/DEM2	No soft-start or DEM mode operation in CH-2	B
10	EN2	No switching in CH-2	B
11	DIR2	Invalid DIR command and no switching in CH-2	B
12	VDD	Normal operation can not be ensured	B
13	HV2	CH-2 Unable to startup	B
14	HB2	Loss of CH-2 Buck Mode Operation	C
15	HO2	Loss of CH-2 Buck Mode Operation	C
16	SW2	Loss of CH-2 Buck Mode Operation	C
17	LO2	Loss of CH-2 Buck Mode Operation	C
18	PGND	No switching	B
19	VCC	No switching	B
20	LO1	Loss of CH-1 Boost Mode Operation	C
21	SW1	Loss of CH-1 Boost Mode Operation	C
22	HO1	Loss of CH-1 Boost Mode Operation	C
23	HB1	Loss of CH-1 Boost Mode Operation	C
24	HV1	CH-1 Unable to Startup	B
25	LDODRV	Normal operation, but VCC pin must be supplied externally	D
26	DIR1	Invalid DIR command and no switching in CH-1	B
27	EN1	No CH-1 switching	B
28	SS/DEM1	No soft-start or DEM mode operation in CH-1	B
29	COMP1	Loss of CH-1 loop compensation and loss of loop stability	B
30	ISET1	Loss of current setting command in CH-1	B
31	CSB1	Loss of CH-1 current regulation	B
32	CSA1	Loss of CH-1 current regulation	B
33	IMON1	Normal operation, but loss of CH-1 current monitor	D
34	EERHV	No switching	B
35	FBHV	No switching	B
36	OVP	Normal operation. Loss of 48V OVP in CH-1 or both channels in parallel operation	D
37	SDA	Normal operation but no I2C communication	D
38	SCL	Normal operation but no I2C communication	D
39	SYNCO	Normal operation, loss of synchronization	D
40	SYNCI	Normal operation, loss of synchronization	D
41	OPT	Normal operation, in 120 degree interleaving	D
42	OSC	Loss of clock function, No switching	B
43	AGND	Loss of analog reference ground. No switching	B
44	CFG	Normal operation, but loss of current monitor and I2C Interface	D
45	UVLO	Unable to startup	B
46	DT/SD	Normal switching with built-in adaptive dead time scheme	D
47	IPK	No switching	B
48	VSET	No switching	B

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

Pin No	Pin Name	Description of Potential Failure Effect (s)	Failure Effect Class
1	VREF	Loss of loop control and no switching activity in Buck Mode	C
2	FBLV	Loss of loop control and no switching activity in Buck Mode	C
3	ERRLV	Loss of loop control and no switching activity in Buck Mode	C
4	IMON2	Pin voltage rating is exceeded and may cause pin damage when shorted to 12V rail	B
5	CSA2	Loss of current sense and loss of CH-2 current regulation	B
6	CSB2	Loss of current sense and loss of CH-2 current regulation	B
7	ISET2	Loss of current setting command, Pin voltage rating is exceeded and may cause pin damage when shorted to CSB2	B
8	COMP2	Loop compensation may be altered by SS capacitor and causing instable operation	B
9	SS/DEM2	Normal operation without soft-start or DEM mode operation in CH-1	D
10	EN2	Normal operation in Buck Mode, no Boost Mode in CH-2	C
11	DIR2	Normal operation in Buck Mode, no Boost Mode in CH-2	C
12	VDD	Normal operation in Buck Mode, no Boost Mode in CH-2	C
13	HV2	No switching in CH-2	B
14	HB2	Pin voltage rating is exceeded and may cause pin damage when shorted to HV2	B
15	HO2	Pin voltage rating is exceeded and may cause pin damage when shorted to SW2	B
16	SW2	No switching in CH-2	B
17	LO2	Pin voltage rating is exceeded and may cause pin damage when shorted to HV2	B
18	PGND	No switching on LO2 when LO2 is shorted to ground rail. Unable to startup when VCC rail is shorted to ground rail	B
19	VCC	Unable to startup when VCC rail is shorted to ground rail. No switching on LO1 when LO1 is shorted to VCC rail	B
20	LO1	Pin voltage rating is exceeded and may cause pin damage when shorted to SW1	B
21	SW1	No switching in CH-1	B
22	HO1	Pin voltage rating is exceeded and may cause pin damage when shorted to SW1	B
23	HB1	Pin voltage rating is exceeded and may cause pin damage when shorted to HV1	B
24	HV1	No switching in CH-1	B
25	LDODRV	Normal operation	D
26	DIR1	Normal operation in Buck Mode, no Boost Mode in CH-1 when shorted to EN1, Pin voltage rating is exceeded and may cause pin damage when shorted to LDODRV	C
27	EN1	Normal operation in Buck Mode, no Boost Mode in CH-1	C
28	SS/DEM1	Normal operation without soft-start or DEM mode operation in CH-1	D
29	COMP1	Loop compensation may be altered by SS capacitor and causing instable operation	B
30	ISET1	Loss of current setting command, Pin voltage rating is exceeded and may cause pin damage when shorted to CSB1	B
31	CSB1	Loss of current sense and loss of CH-1 current regulation	B
32	CSA1	Loss of current sense and loss of CH-1 current regulation	B
33	IMON1	Normal operation with loss of CH-1 current monitor, Pin voltage rating is exceeded and may cause pin damage when shorted to CSA1	D
34	EERHV	Loss of loop control and no switching activity in Boost Mode	C
35	FBHV	Loss of loop control and no switching activity in Boost Mode	C
36	OVP	Normal operation. Loss of 48V OVP in CH-1 or both channels in parallel operation	D
37	SDA	Normal operation but no I2C communication	D
38	SCL	Normal operation but no I2C communication	D
39	SYNCO	Normal operation, loss of synchronization	D
40	SYNCI	Normal operation, loss of synchronization	D
41	OPT	Unreliable clock interleaving may affect operation	B
42	OSC	Unpredictable clock function, unpredictable switching behavior	B
43	AGND	Unpredictable clock function, unpredictable switching behavior	B
44	CFG	Normal operation, but current monitor function not available	D
45	UVLO	Normal operation with unpredictable DT setting when shorted to DT/SD pin	D
46	DT/SD	Normal operation with unpredictable DT setting when shorted to DT/SD pin	D
47	IPK	Unreliable peak current setting and unpredictable switching behavior	B
48	VSET	Unpredictable switching behavior	B