SFFS301 May 2025 LM74720-Q1
4 Pin Failure Mode Analysis (Pin FMA)
This section provides a failure mode analysis (FMA) for the pins of the LM74720-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 supply (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 LM74720-Q1 pin diagram. For a detailed description of the device pins please refer to the Pin Configuration and Functions section in the LM74720-Q1 data sheet.
Figure 4-1 WSON 12-Pin DRR Transparent Top ViewFollowing are the assumptions of use and the device configuration assumed for the pin FMA in this section:
- The device is operating under the specified ranges within the Recommended Operating Conditions section of the data sheet.
Table 4-2 Pin FMA for Device Pins Short-Circuited to Ground
| Pin Name | Pin No. | Description of Potential Failure Effects | Failure Effect Class |
|---|---|---|---|
| DGATE | 1 | The device is damaged due to internal conduction. The external DGATE FET can also be damaged due to a violation of the maximum VGS rating. | A |
| A | 2 | Input supply shorted to ground. Device not functional. | B |
| VSNS | 3 | The input supply monitoring feature is not available. | B |
| SW | 4 | No device damage is expected if VSNS is floating. The device is damaged if VSNS is connected to A. | A |
| OV | 5 | The overvoltage protection functionality is disabled. | B |
| EN | 6 | The device is in shutdown mode. | B |
| GND | 7 | No impact on device functionality. | D |
| PD | 8 | The HGATE gate drive is off. | B |
| LX | 9 | The externals FETs are always OFF. VBATT is short to GND; the inductor can be damaged. | A |
| CAP | 10 | The device is damaged due to internal conduction between VS and CAP. | A |
| VS | 11 | The device does not power up. BFET is damaged. VBATT is short to GND. | A |
| C | 12 | BFET is damaged. VBATT is short to GND. | A |
Table 4-3 Pin FMA for Device Pins Open-Circuited
| Pin Name | Pin No. | Description of Potential Failure Effects | Failure Effect Class |
|---|---|---|---|
| GATE | 1 | The external FET is not controlled. The system is still protected by the body diode of the FET. | B |
| A | 2 | The DGATE drive is off. The system is still protected by the body diode of the FET. | B |
| VSNS | 3 | The input supply monitoring feature is not available. | B |
| SW | 4 | The input supply monitoring feature is not available. | B |
| OV | 5 | The overvoltage pin is internal pulldown when floating. OV functionality is DISABLED. | B |
| EN | 6 | The device is in shutdown mode due to the internal pulldown on the EN pin. | B |
| GND | 7 | The device does not power up. | B |
| PD | 8 | The HFET is off since the PD gate drive is open. | B |
| LX | 9 | The boost output does not switch. BFET is OFF. The output is at VIN-2VD. | B |
| CAP | 10 | The device detects CAP open and shuts off. | B |
| VS | 11 | The boost converter is OFF due to no supply. Both FETS are OFF. | B |
| C | 12 | The part powers up but latches off after one full boost cycle. The latch is cleared by the EN pin or power cycling. | 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 |
|---|---|---|---|---|
| GATE | 1 | A | The DGATE FET is always off as the external FET GATE to SOURCE is shorted. | B |
| A | 2 | VSNS | No impact on device functionality. | D |
| VSNS | 3 | SW | The input supply monitoring feature is always available. There is a higher system Iq when EN = low, due to constant current drawn through the external R-ladder. | B |
| SW | 4 | OV | The PD turns off, provided the voltage of the SW pin is higher than the overvoltage threshold of the overvoltage comparator. | B |
| OV | 5 | EN | The PD is on or off based on the voltage level of the EN/UVLO pin being lower or higher than the overvoltage threshold of the overvoltage comparator. | B |
| EN | 6 | GND | The device is always OFF. No impact on device operation. | B |
| GND | 7 | PD | The PD is pulled low and the external FET is off. | B |
| PD | 8 | LX | N/A | B |
| LX | 9 | CAP | The boost converter diode is bypassed. The device shuts off boost after detecting the fault. | B |
| CAP | 10 | VS | The boost operation is in closed loop (the inductor builds up from C and discharges back to VS or C) at every switching cycle. Continuous switching of boost. | B |
| VS | 11 | C | VS follows C. No impact on device operation. | D |
| C | 12 | N/A | No impact on device operation. | D |
Table 4-5 Pin FMA for Device Pins Short-Circuited to Supply
| Pin Name | Pin No. | Description of Potential Failure Effects | Failure Effect Class |
|---|---|---|---|
| GATE | 1 | The diode FET is always off since the external FET GATE to SOURCE is shorted. | B |
| A | 2 | No impact on device operation. | D |
| VSNS | 3 | No impact on device operation. | D |
| SW | 4 | The input supply monitoring feature is always available. | B |
| OV | 5 | When the input of the overvoltage comparator is higher than the overvoltage threshold, the PD is off. | B |
| EN | 6 | The device is always on. The undervoltage functionality is not available. | B |
| GND | 7 | The input supply is shorted to ground. The device does not power up. | B |
| PD | 8 | The PD gate drive is off when EN = high. The PD internal pulldown FET is damaged when EN = low. | A |
| LX | 9 | The device shuts off boost after detecting the fault. | B |
| CAP | 10 | The charge pump does not power up. DGATE and HGATE drive remain off. | B |
| VS | 11 | No impact on the operation of the device when the supply voltage is positive. The device is damaged when the supply voltage is negative. | A |
| C | 12 | The reverse-current blocking functionality is lost when the supply is positive. The device is damaged when the supply voltage is negative. | A |