SFFS125 June 2021 SN74HCS74-Q1

4 Pin Failure Mode Analysis (Pin FMA)

This section provides a Failure Mode Analysis (FMA) for the pins of the SN74HCS74-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 V_CC (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 SN74HCS74-Q1 pin diagram. For a detailed description of the device pins please refer to the Pin Configuration and Functions section in the SN74HCS74-Q1 data sheet.

Figure 4-1 Pin Diagram

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

Pin Name	Pin Number	Description of Potential Failure Effect(s)	Failure Effect Class
1CLR; 1D; 1CLK; 1PRE; 2PRE; 2CLK; 2D; 2CLR	1; 2; 3; 4; 5; 10; 11; 12; 13	Input pin functionality is defined such as input is LOW – See Device Function Table	B
1Q; 1Q; 2Q; 2Q	5; 6; 8; 9	Can cause excessive output current; output will not switch (For example, if buffer output is shorted to ground and is attempting to drive to VCC).	A
V_CC	14	The device is not powered, because short is external to the device. System level damage may occur in this scenario.	B
GND	7	Normal operation.	D
PAD	—	Normal operation.	D

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

Pin Name	Pin Number	Description of Potential Failure Effect(s)	Failure Effect Class
1CLR; 1D; 1CLK; 1PRE; 2PRE; 2CLK; 2D; 2CLR	1; 2; 3; 4; 5; 10; 11; 12; 13	The pin is floating, and it can change the output state and cause excessive current to flow from V_CC to GND. Refer to the Implications of Slow or Floating CMOS Inputs section in the SN74HCS74-Q1 application note for more information.	A
1Q; 1Q; 2Q; 2Q	5; 6; 8; 9	Normal operation.	D
V_CC	14	The device is not powered.	B
GND	7	The device is not powered.	B
PAD	—	Normal operation.	D

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

Pin Name	Shorted to	Description of Potential Failure Effect(s)	Failure Effect Class
1CLR; 1D; 1CLK; 1PRE; 2PRE; 2CLK; 2D; 2CLR	1CLR; 1D; 1CLK; 1PRE; 2PRE; 2CLK; 2D; 2CLR	Two inputs shorted together will not cause damage unless there is an external bus contention that drives the input (such that VIL<Input Voltage<VIH), in which case excessive supply current to GND may cause damage. System level damage may occur in this scenario.	A
1CLR; 1D; 1CLK; 1PRE; 2PRE; 2CLK; 2D; 2CLR	1Q; 1Q; 2Q; 2Q	Can cause excessive output current, output will not switch (for example, if inverter input is shorted to output).	A
1CLR; 1D; 1CLK; 1PRE; 2PRE; 2CLK; 2D; 2CLR	GND	See Table 4-2 input response for more information.	A
1CLR; 1D; 1CLK; 1PRE; 2PRE; 2CLK; 2D; 2CLR	V_CC	See Table 4-5 input response for more information.	A
1Q; 1Q; 2Q; 2Q	1Q; 1Q; 2Q; 2Q	Can cause excessive output current, and the output will not switch (for example, if one output is driving to VCC and another output is driving to GND).	A
1Q; 1Q; 2Q; 2Q	GND	See Table 4-2 output response for more information.	A
1Q; 1Q; 2Q; 2Q	V_CC	See Table 4-5 output response for more information.	A
GND	V_CC	The device is not powered, because short is external to the device. System level damage may occur in this scenario.	B
PAD	V_CC	The device is not powered, because short is external to the device. System level damage may occur in this scenario.	B
PAD	Inputs/Outputs	Can cause excessive output current, output will not switch.	A

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

Pin Name	Pin Number	Description of Potential Failure Effect(s)	Failure Effect Class
1CLR; 1D; 1CLK; 1PRE; 2PRE; 2CLK; 2D; 2CLR	1; 2; 3; 4; 5; 10; 11; 12; 13	The input pin functionality is defined as high input. For example, if the buffer input is V_CC, then the output will always be driven high.	B
1Q; 1Q; 2Q; 2Q	5; 6; 8; 9	Can cause excessive output current, and the output will not switch (for example, if the buffer output is shorted to V_CC and is attempting to drive to GND).	A
V_CC	14	Normal operation.	D
GND	7	The device is not powered, because short is external to the device. System level damage may occur in this scenario.	B
PAD	—	The device is not powered, because short is external to the device. System level damage may occur in this scenario.	B