SNVA957A April 2020 – May 2022 LM62440-Q1
4 Pin Failure Mode Analysis (Pin FMA)
This section provides a failure mode analysis (FMA) for the pins of the LM62440-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 LM62440-Q1 pin diagram. For a detailed description of the device pins, see the Pin Configuration and Functions section in the LM62440-Q1 Automotive 3-V to 36-V, 4-A, Low-Noise Synchronous Step-Down Converter data sheet.
Figure 4-1 Pin DiagramThe following are the assumptions of use and the device configuration assumed for the pin FMA in this section:
- The application circuit, as per the LM62440-Q1 Automotive 3-V to 36-V, 4-A, Low-Noise Synchronous Step-Down Converter data sheet is used.
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 |
|---|---|---|---|
| BIAS | 1 | Normal operation if the pin is not tied directly to VOUT. VOUT = 0 V if tied directly to VOUT. | B |
| VCC | 2 | VOUT = 0 V | B |
| AGND | 3 | Normal operation | D |
| FB (ADJ option) | 4 | VOUT >> than programmed output voltage | B |
| FB (3.3 V or 5 V option) | 4 | VOUT = 0 V if the pin has no resistor between VOUT and FB. Otherwise, VOUT >> than programmed output voltage. | B |
| PGOOD | 5 | PGOOD is not valid signal. VOUT is in regulation. | D |
| MODE/SYNC | 6 | Auto mode with spread spectrum operation | C |
| EN | 7 | VOUT = 0 V | B |
| VIN1 | 8 | VOUT = 0 V | B |
| PGND1 | 9 | Normal operation | D |
| SW | 10 | Damage to the HS FET | A |
| PGND2 | 11 | Normal operation | D |
| VIN2 | 12 | VOUT = 0 V | B |
| RBOOT | 13 | VOUT = 0 V | A |
| CBOOT | 14 | VOUT = 0 V | B |
Table 4-3 Pin FMA for Device Pins Open-Circuited
| Pin Name | Pin No. | Description of Potential Failure Effect(s) | Failure Effect Class |
|---|---|---|---|
| BIAS | 1 | Normal operation | D |
| VCC | 2 | VCC output is unstable and can increase above 5.5-V rating of the VCC pin. | A |
| AGND | 3 | VOUT can be abnormal due to switching noise on analog circuits. | B |
| FB | 4 | VOUT >> than programmed output voltage | B |
| PGOOD | 5 | PGOOD not valid signal. VOUT is in regulation. | D |
| MODE/SYNC | 6 | Auto mode versus FPWM operation and spread spectrum cannot be predicted. | C |
| EN | 7 | Unpredictable operation | B |
| VIN1 | 8 | VOUT is normal. Current loop is affected, potentially affecting noise, jitter, EMI, and reliability. | C |
| PGND1 | 9 | VOUT is normal. Current loop is affected, potentially affecting noise, jitter, EMI, and reliability. | C |
| SW | 10 | VOUT = 0 V | B |
| PGND2 | 11 | VOUT is normal. Current loop is affected, potentially affecting noise, jitter, EMI, and reliability. | C |
| VIN2 | 12 | VOUT is normal. Current loop is affected, potentially affecting noise, jitter, EMI, and reliability. | C |
| RBOOT | 13 | VOUT normal, low efficiency | C |
| CBOOT | 14 | VOUT = 0 V | B |
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 |
|---|---|---|---|---|
| BIAS | 1 | VCC | VCC ESD clamp is damaged if BIAS > 5.5 V. | A |
| VCC | 2 | AGND | VOUT = 0 V | B |
| AGND (ADJ option) | 3 | FB | VOUT >> than programmed output voltage | B |
| AGND (3.3 V or 5 V option) | 4 | FB | VOUT = 0 V if there is no resistor between VOUT and FB. Otherwise, VOUT >> than the programmed output voltage. | B |
| FB (ADJ option) | 4 | PGOOD | VOUT = 0 V. Damage if PGOOD > 16 V | A |
| FB ((3.3 V or 5 V option) | 4 | PGOOD | VOUT is normal. PGOOD is damaged if there is no resistor between FB and VOUT. VOUT = 0 V, otherwise, damage if PGOOD > 16 V. | A |
| PGOOD | 5 | MODE/SYNC | VOUT normal. The device operates in auto mode with spread spectrum after start-up. | D |
| MODE/SYNC | 6 | EN | VOUT normal, the devices operates in FPWM mode with no spread spectrum. | D |
| EN | 7 | VIN1 | Normal operation | D |
| VIN1 | 8 | PGND1 | VOUT = 0 V. Damage to low-side circuitry if PGND >> AGND | B |
| PGND1 | 9 | SW | Damage to the HS FET | A |
| SW | 10 | PGND2 | Damage to the HS FET | A |
| PGND2 | 11 | VIN2 | VOUT = 0 V. Damage to low-side circuitry if PGND >> AGND | B |
| VIN2 | 12 | RBOOT | VOUT = 0 V. RBOOT ESD clamp runs current to destruction. | A |
| RBOOT | 13 | CBOOT | VOUT is normal. | D |
| CBOOT | 14 | BIAS | VOUT = 0 V | B |
Table 4-5 Pin FMA for Device Pins Short-Circuited to
supply
| Pin Name | Pin No. | Description of Potential Failure Effect(s) | Failure Effect Class |
|---|---|---|---|
| BIAS | 1 | If VIN exceeds 16 V, damage occurs. If VIN is below 16 V, normal operation | A |
| VCC | 2 | If VIN exceeds 5.5 V, damage occurs. | A |
| AGND | 3 | VOUT = 0 V. Damage to other pins referred to GND | A |
| FB | 4 | If VIN exceeds 16 V, damage occurs. VOUT = 0 V | A |
| PGOOD | 5 | VOUT = 0 V. PGOOD ESD clamp runs current to destruction. | A |
| MODE/SYNC | 6 | VOUT is normal. The part runs in FPWM mode without spread spectrum. | D |
| EN | 7 | VOUT is normal. | D |
| VIN1 | 8 | Normal operation | D |
| PGND1 | 9 | VOUT = 0 V. Damage to low-side circuitry if PGND >> AGND | B |
| SW | 10 | Damage to the LS FET | A |
| PGND2 | 11 | VOUT = 0 V. Damage to low-side circuitry if PGND >> AGND | B |
| VIN2 | 12 | Normal operation | D |
| RBOOT | 13 | VOUT = 0 V. RBOOT ESD clamp runs current to destruction. | A |
| CBOOT | 14 | VOUT = 0 V. CBOOT ESD clamp runs current to destruction. | A |