SFFS313 November 2021 UCC28781-Q1

4 Pin Failure Mode Analysis (Pin FMA)

This section provides a failure mode analysis (FMA) for the pins of the UCC28781-Q1. 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 UCC28781-Q1 pin diagram. For a detailed description of the device pins, see the Pin Configuration and Functions section in the UCC28781-Q1 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:

IC is set up according to the typical application circuit shown in UCC28781-Q1 datasheet Figure 11-1
VDD pin is considered as the supply pin

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
FLT	1	IC enters fault mode, no PWML or PWMH output.	B
RTZ	2	Pin short protection. IC tries to restart. Converter has no output.	B
RDM	3	Pin short protection. IC tries to restart. Converter has no output.	B
IPC	4	No impact on operation. Converter operates with slightly lower efficiency at light load.	C
BUR	5	Burst mode threshold sets to minimum. Light load efficiency will be worse.	C
FB	6	Converter delivers minimum power. PWML with minimum on time. No PWMH output.	B
REF	7	No PWML or PWMH output. Converter has no output.	B
AGND	8	No effect.	D
CS	9	Controller enters CS pin short protection. IC tries to restart. Converter has no output.	B
RUN	10	VREF overload. IC shuts down and retries.	B
PGND	11	No effect.	D
PWML	12	PWML has no output. IC protects and retries after UVLO.	B
S13	13	No PWML or PWMH output. Converter has no output.	B
P13	14	No PWML or PWMH output. Converter has no output.	B
PWMH	15	VREF overload. IC shuts down and retries.	B
SWS	16	IC can't start up.	B
XCD	17	XCD function is lost. Possible damage on the line sensing device.	B
XCD	18	XCD function is lost. Possible damage on the line sensing device.	B
VDD	19	No PWML or PWMH output. Converter has no output.	B
GTP1	20	No effect.	D
GTP2	21	No effect.	D
GTP3	22	No effect.	D
VS	23	Controller enters brownout protection. IC enters UVLO mode and retries.	B
SET	24	Configure to GaN MOSFET. Either no impact, or converter operates with worse efficiency.	C

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

Pin Name	Pin No.	Description of Potential Failure Effect(s)	Failure Effect Class
FLT	1	No impact on operation. IC loses FLT pin fault protection function.	C
RTZ	2	RTZ pin open pin protection. IC tries to restart. Converter has no output.	B
RDM	3	RDM pin open pin protection. IC tries to restart. Converter has no output.	B
IPC	4	No impact on operation. Converter operates with slightly higher efficiency at light load. Converter might have audible noise.	C
BUR	5	Burst level sets to highest. Burst mode threshold and the light load efficiency will be different.	C
FB	6	OVP is triggered. IC shuts down and retries.	B
REF	7	No effect. IC might shutdown due to the noise coupling into REF pin.	C
AGND	8	Behavior can be unpredictable. IC damage is possible.	A
CS	9	CS pin open protection. IC enters UVLO mode and retries.	B
RUN	10	No effect.	D
PGND	11	Behavior can be unpredictable. IC damage is possible.	A
PWML	12	Converter has no output.	B
S13	13	No effect.	D
P13	14	P13 pin open pin protection.	B
PWMH	15	No SR driver signal, converter operates with less efficiency. Power stage might get damaged.	C
SWS	16	IC does not start.	B
XCD	17	No effect.	D
XCD	18	No effect.	D
VDD	19	IC is not biased. No PWML or PWMH output.	B
GTP1	20	No effect.	D
GTP2	21	No effect.	D
GTP3	22	No effect.	D
VS	23	IC enters protection mode, shuts down and retries.	B
SET	24	IC sets to Si MOSFET mode. Either no impact or converter operates with worse efficiency	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
FLT	1	RTZ	RTZ pin setting is wrong. Converter efficiency will be lower. RTZ pin short protection is possible. IC loses FLT pin fault protection function.	C
RTZ	2	RDM	RDM pin open protection. IC tries to restart. Converter has no output.	B
RDM	3	IPC	RDM pin short protection. IC tries to restart. Converter has no output.	B
IPC	4	BUR	Burst level is lower than designed. Wrong burst threshold. Converter light load efficiency might be worse.	C
BUR	5	FB	Burst level is higher than designed. Wrong burst threshold. Converter light load efficiency might be different. The converter might reduce its maximum power handling capability.	C
FB	6	N/A	N/A	N/A
REF	7	AGND	No PWML or PWMH output. Converter has no output.	B
AGND	8	CS	IC enters CS pin short protection. IC enters UVLO mode and retries.	B
CS	9	RUN	IC shuts down and retries. Converter has no output.	B
RUN	10	PGND	VREF overload protection. IC shuts down and retries.	B
PGND	11	PWML	VREF overload protection. IC shuts down and retries.	B
PWML	12	N/A	N/A	N/A
S13	13	P13	No impact.	D
P13	14	PWMH	PWMH stays high. Possible IC and power stage damage.	A
PWMH	15	SWS	IC can't start up.	B
SWS	16	XCD	XCD function is lost.	C
XCD	17	XCD	No effect.	D
XCD	18	N/A	N/A	N/A
VDD	19	GTP1	IC is not biased. No PWML or PWMH output.	B
GTP1	20	GTP2	No effect.	D
GTP2	21	GTP3	No effect.	D
GTP3	22	VS	IC can't start up.	B
VS	23	SET	IC can't start up.	B
SET	24	N/A	N/A	N/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
FLT	1	IC enters protection mode. Possible IC damage.	A
RTZ	2	IC shuts down and retries. Possible IC damage.	A
RDM	3	IC shuts down and retries. Possible IC damage.	A
IPC	4	IC operates with higher peak current at light load mode. Possible IC damage.	A
BUR	5	IC shuts down and retries. Possible IC damage.	A
FB	6	IC triggers OVP protection. Possible IC damage.	A
REF	7	IC enters protection mode. Possible IC damage.	A
AGND	8	IC is not biased. No PWML or PWMH output. Converter has no output	B
CS	9	IC enters protection mode. Possible IC damage.	A
RUN	10	IC enters protection mode. Possible IC damage.	A
PGND	11	IC is not biased. No PWML or PWMH output. Converter has no output.	B
PWML	12	IC can't start up.	B
S13	13	IC can't start up.	B
P13	14	IC can't start up.	B
PWMH	15	IC can't start up.	B
SWS	16	IC tries to start up. Possible power stage damage.	B
XCD	17	XCD function is lost. Possible IC damage if VDD exceeds 30V.	A
XCD	18	XCD function is lost. Possible IC damage if VDD exceeds 30V.	A
VDD	19	No effect	D
GTP1	20	IC is not biased. No PWML or PWMH output. Converter has no output.	B
GTP2	21	IC is not biased. No PWML or PWMH output. Converter has no output.	B
GTP3	22	IC is not biased. No PWML or PWMH output. Converter has no output.	B
VS	23	OVP is triggered. IC shuts down and retries. Possible IC damage.	A
SET	24	IC sets to Si MOSFET mode. Possible IC damage.	A