SFFS410 July 2022 LM73605
4 Pin Failure Mode Analysis (Pin FMA)
This section provides a failure mode analysis (FMA) for the pins of the LM73605. 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)
Table 4-2 through Table 4-4 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 LM73605 pin diagram. For a detailed description of the device pins, see the Pin Configuration and Functions section in the LM73605 data sheet.
Figure 4-1 Pin DiagramFollowing are the assumptions of use and the device configuration assumed for the pin FMA in this section:
- Application Circuit as per the
LM73605 data sheet is
used
- PG is pulled up to VOUT
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 |
|---|---|---|---|
| SW | 1, 2, 3, 4, 5 | Shorting the SW pin to ground results in large currents through the device and subsequent damage. No output voltage is produced. | A |
| CBOOT | 6 | Driver supply to the high-side MOSFET is lost. Output voltage is not regulated. Possible damage to internal regulator and CBOOT charging circuit | B |
| VCC | 7 | Internal circuits are disabled. No output voltage is generated. Possible increase in input current and possible damage to internal LDO | C |
| BIAS | 8 | A valid connection for the BIAS input. The internal LDO is powered from the input voltage. | D |
| RT | 9 | The device is incapable of switching, and no output voltage is produced. | C |
| SS/TRK | 10 | The device does not start up. No signal on switch and no output voltage is produced. | C |
| FB | 11 | The regulator operates at maximum duty cycle. Output voltage rises to nearly the input voltage level. Possible damage to customer load, output stage components, or both, can occur. | B |
| NC | 12, 13, 14, 15 | No risk | D |
| PGOOD | 16 | A valid connection for the PG output. PG functionality is lost. Damage to customer components connected to PG input can occur. | C |
| SYNC/MODE | 17 | A valid connection for the SYNC/MODE input. Enable auto mode operation. | D |
| EN | 18 | A valid connection for the EN input. Enable functionality is lost; the device remains off with no output voltage generated. Damage to customer components connected to EN input can occur. | D |
| AGND | 19 | No risk. Ground pin | D |
| VIN | 20, 21, 22 | No output voltage is generated. Possible damage to customer input supply, PCB, or both, can occur unless customer provides protection. Reverse current from SW pin to VIN pin due to discharge of output capacitors can damage the regulator. | B |
| PGND | 23, 24, 25, 26 | No risk. Ground pin | D |
| NC | 27, 28, 29, 30 | No risk | D |
Table 4-3 Pin FMA for Device Pins Open-Circuited
| Pin Name | Pin No. | Description of Potential Failure Effect(s) | Failure Effect Class |
|---|---|---|---|
| SW | 1, 2, 3, 4, 5 | Loss of output voltage | B |
| CBOOT | 6 | Driver supply to high-side MOSFET is lost. Output voltage is not regulated. Low or no output voltage; erratic switching behavior | B |
| VCC | 7 | Internal LDO can oscillate. VCC voltage is not stable. Internal circuits do not function correctly. Output voltage may not be regulated. Damage to internal LDO is possible. | A |
| BIAS | 8 | The internal LDO is be powered from the input voltage. | D |
| RT | 9 | A valid condition for the RT pin. The device uses the default switching frequency of 500 kHz. | C |
| SS/TRK | 10 | A valid condition for the SS/TRK pin. The device uses the internal soft-start ramp. | D |
| FB | 11 | The device does not regulate. Output voltage can rise or fall. Damage to customer load, output stage components, or both, is possible. | B |
| NC | 12, 13, 14, 15 | No risk | D |
| PGOOD | 16 | A valid connection for the PG output. PG functionality is lost. | C |
| SYNC/MODE | 17 | Floating this pin can cause unexpected operation mode. | B |
| EN | 18 | Loss of enable functionality. Erratic operation; probable loss of regulation | B |
| AGND | 19 | Erratic operation; probable loss of regulation. Possible output voltage increase and damage to customer load | B |
| VIN | 20, 21, 22 | Loss of output voltage | B |
| PGND | 23, 24, 25, 26 | Erratic operation; probable loss of regulation. Possible output voltage increase and damage to customer load | B |
| NC | 27, 28, 29, 30 | No risk | D |
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 |
|---|---|---|---|---|
| SW | 1, 2, 3, 4, 5 | CBOOT | Boot capacitor does not charge. Erratic operation with loss of regulation | B |
| CBOOT | 6 | VCC | Damage to VCC regulator, other internal circuits, or both. Output voltage can be affected. | A |
| VCC | 7 | BIAS | FETs are undersupplied. No regulation on output. Unloaded device is able to regulate. | A |
| BIAS | 8 | RT | Internal circuits are disabled. No output voltage is generated. Possible increase in input current and possible damage to internal LDO | A |
| RT | 9 | SS/TRK | Internal circuits are disabled. No output voltage is generated. | B |
| SS/TRK | 10 | FB | The regulator operates at maximum duty cycle. Output voltage rises to nearly the input voltage level. Possible damage to customer load, output stage components, or both, can occur. | B |
| FB | 11 | NC | When NC is not connected, there is no issue. | D |
| When connecting NC to ground, the regulator operates at maximum duty cycle. Output voltage rises to nearly the input voltage level. Possible damage to customer load, output stage components, or both, can occur. | B | |||
| NC | 12, 13, 14, 15 | PG | When NC is not connected, there is no issue. | D |
| When connecting NC to ground, the PGOOD pin is shorted to ground. Consequently, the PGOOD output is not functional. | C | |||
| PG | 16 | SYNC/MODE | When SYNC/MODE is tied low: the PGOOD pin is shorted to ground. Consequently, the PGOOD output is not functional. If PGOOD is tied to VOUT, then the output voltage is shorted and the device enters hiccup operation. | C |
| When SYNC/MODE is tied high: if PGOOD is shorted to VOUT < 5.5 V, possible damage to customer load, output stage components, or both, can occur. | B | |||
| When SYNC/MODE is tied high: if PGOOD is > 5.5 V, this exceeds to the absolute maximum of SYNC/MODE. The device is at risk to be damaged. | A | |||
| SYNC/MODE | 17 | EN | When SYNC/MODE is tied low: a valid connection for the EN input. Enable functionality is lost; the device remains off with no output voltage generated. | B |
| When SYNC/MODE is tied high to external supply: a valid connection for the EN input. Enable functionality is lost; the device remains on. | C | |||
| When SYNC/MODE is tied high to VCC: if short occurs before start-up, the device does not start up. If short occurs during regulation, enable functionality is lost and the device remains on. | B | |||
| EN | 18 | AGND | A valid connection for the EN input. Enable functionality is lost; the device remains off with no output voltage generated. | B |
| AGND | 19 | PVIN | No output voltage is generated. Possible damage to customer input supply, PCB, or both, can occur unless customer provides protection. Reverse current from SW pin to the VIN pin due to discharge of output capacitors can damage regulator. | B |
| PVIN | 20, 21, 22 | PGND | No output voltage is generated. Possible damage to customer input supply, PCB, or both, can occur unless customer provides protection. Reverse current from SW pin to the VIN pin due to discharge of output capacitors can damage regulator. | B |
| PGND | 23, 24, 25, 26 | NC | No issue. PGND is a valid connection for NC. | D |
| NC | 27, 28, 29, 30 | SW | When NC is floating, there is no issue. | D |
| When NC is connected to GND: this is high risk. Shorting the SW pin to ground results in large currents through the device and subsequent damage. No output voltage is produced. | A |