SFFS366 October 2022 LM5149-Q1
This section provides a Failure Mode Analysis (FMA) for the pins of the LM5149-Q1. The failure modes covered in this document include the typical pin-by-pin failure scenarios:
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.
| 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 LM5149-Q1 pin diagram. For a detailed description of the device pins please refer to the Pin Configuration and Functions section in the LM5149-Q1 data sheet.
Following are the assumptions of use and the device configuration assumed for the pin FMA in this section:
| Pin Name | Pin No. | Description of Potential Failure Effect(s) | Failure Effect Class |
|---|---|---|---|
| AVSS | 1 | AVSS is ground. VOUT = expected VOUT | D |
| INJ | 2 | Active EMI filtering will not work but the regulator will continue regulating. VOUT = expected VOUT | C |
| CNFG | 3 | Active EMI filtering will be disabled. VOUT unaffected | C |
| RT | 4 | VOUT will attempt to regulate at maximum fSW, causing maximum power disippation. | B |
| EXTCOMP | 5 | VOUT = 0 V | B |
| FB | 6 | Internal FB mode, VOUT = expected VOUT | D |
| External FB mode, VOUT = VIN | A | ||
| AGND | 7 | AGND is GND. VOUT = expected VOUT | D |
| VDDA | 8 | VOUT = 0 V, no switching, loaded VCC output | B |
| VCC | 9 | VOUT = 0 V, no switching, loaded VCC output | B |
| PGND | 10 | PGND is GND. VOUT = expected VOUT | D |
| LO | 11 | VOUT = 0 V,VCC regulator loaded to the current limit | B |
| VIN | 12 | VOUT = 0 V | B |
| HO | 13 | VOUT = 0 V, VCC regulator loaded to the current limit | B |
| SW | 14 | VOUT = 0 V. High-side FET is shorted from VIN to GND. | A |
| CBOOT | 15 | VOUT = 0, VCC regulator loaded to the current limit | B |
| VCCX | 16 | VOUT = expected VOUT. The internal VCC regulator provides bias voltage. | C |
| PG | 17 | If in single phase, PG has no effect on operation. VOUT = expected VOUT | C |
| If in interleaved primary mode, the secondary will detect no clock input and will shut down. Secondary phase is disabled and primary phase can current limit. | B | ||
| PFM/SYNC | 18 | VOUT = expected VOUT. No synchronization will be availible and the LM5149-Q1 will be in FPWM mode. | C |
| EN | 19 | VOUT = 0 V. The LM5149-Q1 enters shutdown. | C |
| ISNS+ | 20 | VOUT = 0 V; HO damaged | A |
| VOUT | 21 | VOUT = 0 V. Current limit reached, Hiccup mode occurs. | B |
| AEFVDDA | 22 | AEFVDDA = VCC. VCC is shorted and VOUT = 0 V. VCC loaded | B |
| SEN | 23 | Active EMI filtering will not work but the regulator will continue regulating. VOUT = expected VOUT | B |
| REFAGND | 24 | REFAGND is ground. VOUT = expected VOUT | D |
| Pin Name | Pin No. | Description of Potential Failure Effect(s) | Failure Effect Class |
|---|---|---|---|
| AVSS | 1 | Active EMI filtering will not work but the regulator will continue regulating. VOUT = expected VOUT | C |
| INJ | 2 | Active EMI filtering will not work but the regulator will continue regulating. VOUT = expected VOUT | C |
| CNFG | 3 | VOUT will continue operating normally. CNFG is used during start-up and enables AEF. | C |
| RT | 4 | RT will regulate to 500 mV, but the internal oscillator will not function. | B |
| EXTCOMP | 5 | VOUT will oscillate. If VOUT oscillates to VIN, damage can occur if VIN > 60 V. | A |
| FB | 6 | Internal FB mode, VOUT = expected VOUT | D |
| External FB mode, VOUT = VIN | A | ||
| AGND | 7 | VOUT is indeterminate. | B |
| VDDA | 8 | Poor noise immunity | C |
| VCC | 9 | VOUT = 0 V | B |
| PGND | 10 | VOUT = 0 V | B |
| LO | 11 | VOUT = expected VOUT with reduced efficiency | C |
| VIN | 12 | VOUT = 0 V | C |
| HO | 13 | If HO is opened while HO to SW has voltage, the high-side FET will never turn off. VOUT = VIN | A |
| SW | 14 | VOUT is indeterminate. The CBOOT floating rail has no reference to the actual SW node. VOUT = VIN | A |
| CBOOT | 15 | VOUT = 0 V | B |
| VCCX | 16 | VCCX is held to ground by a weak pulldown. VOUT = expected VOUT | D |
| PG | 17 | If in single phase, PG has no effect on operation. VOUT = expected VOUT | C |
| If in interleaved primary mode, the secondary will detect no clock input and will shut down. The secondary phase is disabled and primary phase can current limit. | B | ||
| PFM/SYNC | 18 | VOUT = expected VOUT | D |
| EN | 19 | VOUT = expected VOUT | D |
| ISNS+ | 20 | The OPEN ISNS+ pin will block current limit and cause VOUT oscillations. | A |
| VOUT | 21 | VOUT = 0 V | B |
| AEFVDDA | 22 | Active EMI filtering will not function. | C |
| SEN | 23 | Active EMI filtering will not function. | C |
| REFAGND | 24 | Active EMI filtering will not function. | C |
| Pin Name | Pin No. | Shorted to | Description of Potential Failure Effect(s) | Failure Effect Class |
|---|---|---|---|---|
| AVSS | 1 | INJ | Active EMI filtering will not function. VOUT = expected VOUT | C |
| INJ | 2 | CNFG | Active EMI filtering will not function. VOUT = expected VOUT | C |
| CNFG | 3 | RT | VOUT = expected VOUT with erractic switching | B |
| RT | 4 | EXTCOMP | COMP cannot regulate down due to clamping by the internal RT. | B |
| EXTCOMP | 5 | FB | External FB Mode: COMP will regulate to .8 V and the output will be unregulated. VOUT = any voltage | B |
| Internal FB Mode: COMP will rise up to VDD. VOUT = VIN | A | |||
| FB | 6 | AGND | External FB Mode: VOUT = VIN | A |
| Internal FB Mode: VOUT = expected VOUT | D | |||
| AGND | 7 | VDDA | VDDA will be grounded. VOUT = 0 V | B |
| VDDA | 8 | VCC | VOUT = expected VOUT | D |
| VCC | 9 | PGND | VCC will be grounded. VOUT = 0 V | B |
| PGND | 10 | LO | VOUT = 0 V. VCC is loaded by LO driver. | B |
| LO | 11 | VIN | VOUT = 0 V. The driver will be damaged if VIN > 6.5 V. | A |
| VIN | 12 | HO | VOUT = VIN | A |
| HO | 13 | SW | VOUT = 0 V | B |
| SW | 14 | CBOOT | VOUT = 0 V | B |
| CBOOT | 15 | VCCX | VOUT < 5 V | A |
| VCCX | 16 | PG | PG pulldown can damage. VOUT = expected VOUT | A |
| PG | 17 | PFM/SYNC | VOUT = expected VOUT | C |
| PFM/SYNC | 18 | EN | VOUT = expected VOUT | A |
| EN | 19 | ISNS+ | EN is high voltage rated. VOUT = expected VOUT if VOUT > 1 V. If VOUT < 1 V, the device is disabled. | B |
| ISNS+ | 20 | VOUT | Current limit is disabled since the current limit resistor would be shorted. VOUT cannot regulate since current mode feedback is shorted. | A |
| VOUT | 21 | AEFVDDA | Active EMI filtering will not function and damage will occur if VOUT > 6.5 V. VOUT = expected VOUT | A |
| AEFVDDA | 22 | SEN | Active EMI filtering will not function. VOUT = expected VOUT | C |
| SEN | 23 | REFAGND | Active EMI filtering will not function. VOUT = expected VOUT | C |
| REFAGND | 24 | AVSS | No impact | D |
| Pin Name | Pin No. | Description of Potential Failure Effect(s) | Failure Effect Class |
|---|---|---|---|
| AVSS | 1 | Active EMI filtering will not function, high VIN current | A |
| INJ | 2 | Active EMI filtering will not function, high VIN current | A |
| CNFG | 3 | VOUT = VIN | A |
| RT | 4 | VOUT = 0 V; High VIN current | A |
| EXTCOMP | 5 | This will bring VDDA up to VIN. VOUT = VIN. | A |
| FB | 6 | This will bring VDDA up to VIN. VOUT = VIN | A |
| AGND | 7 | VOUT = VIN; High VIN current | A |
| VDDA | 8 | If VIN < 6.5 V, VOUT = expected VOUT | D |
| If VIN > 6.5 V, exceeds maximum ratings and VDDA is damaged. | A | ||
| VCC | 9 | If VIN < 6.5 V, VOUT = expected VOUT | D |
| If VIN > 6.5 V, exceeds maximum ratings and VCC is damaged. | A | ||
| PGND | 10 | VOUT = VIN; High VIN current | A |
| LO | 11 | For VIN < 6.5 V, VOUT = 0; excess current from VIN | B |
| For VIN > 6.5 V, exceeds maximum ratings and pin LO is damaged. | A | ||
| VIN | 12 | N/A | D |
| HO | 13 | For VIN < 6.5 V, VOUT = dropout lower than VIN, no switching, excess current from VIN | B |
| For VIN > 6.5 V, exceeds maximum ratings and HO is damaged, VOUT = VIN | A | ||
| SW | 14 | VOUT = VIN, excess current from VIN. LO turns on and shorts against VIN. | A |
| CBOOT | 15 | For VIN < 6.5 V, VOUT = expected VOUT, erratic switching | B |
| For VIN > 6.5 V, exceeds maximum ratings and the CBOOT pin is damaged, HO damaged. VOUT = VIN | A | ||
| VCCX | 16 | If VCCX = VOUT, for VIN < 6.5 V, VOUT = VIN | B |
| For VIN > 6.5 V, exceeds maximum ratings and VCCX is damaged. | A | ||
| PG | 17 | For VIN < 6.5 V, VOUT = expected VOUT, PG forced high | B |
| For VIN > 6.5 V, exceeds maximum ratings and PG is destroyed. | A | ||
| PFM/SYNC | 18 | If PFM = GND, VOUT = 0 V, excess current from VIN | B |
| If PFM = VDDA and VIN < 6.5 V, VOUT = expected VOUT and erratic switching. | B | ||
| If VIN > 6.5 V, exceeds maximum ratings and PFM is damaged. VOUT = expected VOUT | A | ||
| EN | 19 | The part will be always on. VOUT = expected VOUT | C |
| ISNS+ | 20 | If VIN < 60 V, VOUT = VIN | B |
| If VIN > 60 V, exceeds maximum ratings and CS is damaged. | A | ||
| VOUT | 21 | If VIN < 60 V, VOUT = VIN | B |
| If VIN > 60 V, exceeds maximum ratings and CS is damaged. | A | ||
| AEFVDDA | 22 | Active EMI filtering will not function, high VIN current | A |
| SEN | 23 | Active EMI filtering will not function, high VIN current | A |
| REFAGND | 24 | Active EMI filtering will not function, high VIN current | A |