SFFSAN5 July 2025 UCC25661-Q1
4 Pin Failure Mode Analysis (Pin FMA)
This section provides a failure mode analysis (FMA) for the pins of the UCC25661x-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 VCC (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 UCC25661x-Q1 pin diagram. For a detailed description of the device pins, see the Pin Configuration and Functions section in the UCC25661x-Q1 data sheet.
Figure 4-1 Pin DiagramFollowing are the assumptions of use and the device configuration assumed for the pin FMA in this section:
- The analysis is based on the typical application schematic in the UCC25661x-Q1 data sheet.
- VCCP 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 Effects | Failure Effect Class |
|---|---|---|---|
| HV | 1 | The device is not biased. No output. | B |
| N/A | 2 | N/A | N/A |
| BLK | 3 | No output. | B |
| OVP/OTP | 4 | The system tries to restart. No output. | B |
| FB | 5 | The system tries to restart. No output. | B |
| LL | 6 | The burst-mode function is disabled. | C |
| TSET | 7 | The system does not start up. | B |
| V5P | 8 | The system does not start up. | B |
| ISNS | 9 | Protection triggers. No output. | B |
| GNDP | 10 | No effect. | D |
| LO | 11 | The system does not start up. | B |
| VCCP | 12 | The device is not biased. No output. | B |
| N/A | 13 | N/A | N/A |
| HB | 14 | The device is not biased. No output. | B |
| HO | 15 | Protection triggers. No output. | B |
| HS | 16 | Half-bridge shoot through; power stage is damaged. No output. | B |
Table 4-3 Pin FMA for Device Pins Open-Circuited
| Pin Name | Pin No. | Description of Potential Failure Effects | Failure Effect Class |
|---|---|---|---|
| HV | 1 | The device is not biased. No output. | B |
| N/A | 2 | N/A | N/A |
| BLK | 3 | No output. | B |
| OVP/OTP | 4 | OVP/OTP loses protections. | C |
| FB | 5 | Protection triggers. No output. | B |
| LL | 6 | The burst-mode function is lost. | C |
| TSET | 7 | The system does not start up. No output. | B |
| V5P | 8 | The output is not regulated. | B |
| ISNS | 9 | The system does not start up. | B |
| GNDP | 10 | The output is not regulated. | B |
| LO | 11 | No output. | B |
| VCCP | 12 | No output. | B |
| N/A | 13 | N/A | N/A |
| HB | 14 | No output. | B |
| HO | 15 | The output is not regulated. | B |
| HS | 16 | Power stage is damaged. No output. | B |
Table 4-4 Pin FMA for Device Pins Short-Circuited to
Adjacent Pin
| Pin Name | Pin No. | Shorted to | Description of Potential Failure Effects | Failure Effect Class |
|---|---|---|---|---|
| HV | 1 | N/A | N/A | D |
| N/A | 2 | BLK | N/A | D |
| BLK | 3 | OVP/OTP | The output is not regulated. | B |
| OVP/OTP | 4 | FB | The output is not regulated. | B |
| FB | 5 | LL | The output is not regulated. | B |
| LL | 6 | TSET | The output is not regulated. | B |
| TSET | 7 | V5P | The system does not start up. | B |
| V5P | 8 | ISNS | N/A | D |
| ISNS | 9 | GNDP | Protection triggers. No output. | B |
| GNDP | 10 | LO | No output. | B |
| LO | 11 | VCCP | No output. | B |
| VCCP | 12 | N/A | N/A | D |
| N/A | 13 | HB | N/A | D |
| HB | 14 | HO | The power stage and device are damaged. | A |
| HO | 15 | HS | No output. | B |
Table 4-5 Pin FMA for Device Pins Short-Circuited to
VCC
| Pin Name | Pin No. | Description of Potential Failure Effects | Failure Effect Class |
|---|---|---|---|
| HV | 1 | The system is in normal operation after the HV series resistor is burned. | C |
| N/A | 2 | N/A | D |
| BLK | 3 | The output is not regulated. | B |
| OVP/OTP | 4 | The output is not regulated. | B |
| FB | 5 | The output is not regulated. | B |
| LL | 6 | The output is not regulated. | B |
| TSET | 7 | The output is not regulated. | B |
| V5P | 8 | The output is not regulated. | B |
| ISNS | 9 | The device is not biased. No output. | B |
| GNDP | 10 | The device is not biased. No output. | B |
| LO | 11 | No output. | B |
| VCCP | 12 | No impact. | D |
| N/A | 13 | N/A | D |
| HB | 14 | The device and system are damaged. | A |
| HO | 15 | The device and system are damaged. | A |
| HS | 16 | The output is not regulated. | B |