SLUAAA8 November 2020 UCC28740-Q1

4 Pin Failure Mode Analysis (Pin FMA)

This section provides a Failure Mode Analysis (FMA) for the pins of the UCC28740-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 UCC28740-Q1 pin diagram. For a detailed description of the device pins please refer to the Pin Configuration and Functions section in the UCC28740-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:

The device is connected according to the design procedure application example shown in Figure 19, in UCC28740-Q1 datasheet
The supply pin refers to VDD 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
VDD	1	Device is not functional, system will not startup.	B
VS	2	IC remains in input under voltage protection mode. The output of the flyback converter remains at zero.	B
FB	3	Device operates at its maximum switching frequency with maximum duty cycle. Output OVP is triggered.	B
GND	4	No effect.	D
CS	5	When CS pin is shorted to ground before the IC startup, CS pin short protection. The output of the flyback converter remains at zero.	B
CS	5	When CS pin is shorted to ground after the IC in operation, potnetial power stage damange and it might cause IC damage.	A
DRV	6	DRV remains low. The output of the flyback converter remains at zero.	B
N/A	7
HV	8	The VDD capacitor cannot be trickle charged and the converter will never startup.	B

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

Pin Name	Pin No.	Description of Potential Failure Effect(s)	Failure Effect Class
VDD	1	No positive supply applied to device, device is not functional.	B
VS	2	IC remains in input under voltage protection mode. The output of the flyback converter remains at zero.	B
FB	3	Device operates at its maximum switching frequency with maximum duty cycle. Output OVP is triggered.	B
GND	4	Device Damage	A
CS	5	CS pin open protection. The output of the Flyback converter remains at zero.	B
DRV	6	The output of the Flyback converter remains at zero.	B
N/A	7
HV	8	The VDD capacitor cannot be trickle charged. Output of the converter remains at zero volts.	B

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
VDD	1	VS	VS max voltage rating exceeded, device damaged, possible Flyback switch damage	A
VS	2	FB	FB will not be stable, output voltage will not regulate correctly	C
FB	3	GND	Device operates at maximum switching frequency with maximum duty cycle. Output over voltage protection will be triggered	B
GND	4	N/A
CS	5	DRV	CS max voltage rating will be exceeded, device damage, possible Flyback switch damage	A
DRV	6	N/A
N/A	7	N/A
HV	8	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
VDD	1	No Effect.	D
VS	2	Pin's maximum voltage rating exceeded, posibble IC damage.	A
FB	3	Pin's maximum voltage rating exceeded, posibble IC damage.	A
GND	4	No positive supply applied to device. Device is non-functional.	B
CS	5	DRV remains low. Possible IC damage.	A
DRV	6	DRV remains high. Possible IC damage and Flyback switch damage.	A
N/A	7
HV	8	The max rating of VDD will be exceeded, possible device damage and Flyback switch damage.	A