SFFS367 December 2022 LM5149
This section provides a Failure Mode Analysis (FMA) for the pins of the LM5149. 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 pin diagram. For a detailed description of the device pins please refer to the Pin Configuration and Functions section in the LM5149 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 will be in FPWM mode. | C |
| EN | 19 | VOUT = 0 V. The LM5149 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 |