SFFS035A December 2020 – February 2022 LM5157-Q1 , LM51571-Q1
4 Pin Failure Mode Analysis (Pin FMA)
This section provides a Failure Mode Analysis (FMA) for the pins of the LM5157-Q1 and LM51571-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 LM5157-Q1 and LM51571-Q1 pin diagram. For a detailed description of the device pins please refer to the Pin Configuration and Functions section in the LM5157-Q1 and LM51571-Q1 data sheet.
Figure 4-1 Pin DiagramFollowing are the assumptions of use and the device configuration assumed for the pin FMA in this section:
- Device used within the Recommended Operating Conditions and the Absolute Maximum Ratings found in the LM5157-Q1 and LM51571-Q1 data sheet.
- Configuration as boost converter as shown in the Application and Implementation found in the LM5157-Q1 and LM51571-Q1 data sheet.
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 |
|---|---|---|---|
| PGND | 1, 16 | No effect. Normal operation | D |
| VCC | 2 | VCC regulator short circuit. The device can shut down due to thermal shutdown. | B |
| BIAS | 3 | The device is unpowered. The device is not functional. | B |
| PGOOD | 4 | Correct output voltage. Loss of power good functionality | B |
| RT | 5 | Switching frequency increased to > 2.2 MHz. The device can be unstable. | B |
| EN/UVLO/SYNC | 6 | EN stuck low. The device is disabled and in shutdown mode. | B |
| AGND | 7 | No effect. Normal operation | D |
| COMP | 8 | Device out of regulation. The device is not switching. | B |
| FB | 9 | Output voltage rises and can exceed the absolute maximum rating of the SW pin voltage. Potential damage to pin | A |
| SS | 10 | During soft start, the SS pin is stuck low. The device does not start up. The device stops switching during operation. | B |
| MODE | 11 | Hiccup mode protection is disabled and spread spectrum is disabled. | B |
| NC | 12, 15 | No effect. Normal operation | D |
| SW | 13, 14 | Potential damage to inductor and pin | A |
Table 4-3 Pin FMA for Device Pins Open-Circuited
| Pin Name | Pin No. | Description of Potential Failure Effect(s) | Failure Effect Class |
|---|---|---|---|
| PGND | 1, 16 | Possible device damage | A |
| VCC | 2 | High ripple on VCC pin that can trigger VCC UVLO | B |
| BIAS | 3 | The device is unpowered. The device is not functional. | B |
| PGOOD | 4 | Correct output voltage. Loss of power-good functionality | C |
| RT | 5 | Internal oscillator is instable or not functional. The device stops switching operation. | B |
| EN/UVLO/SYNC | 6 | State of EN/UVLO/SYNC undetermined. Device can be in shutdown or standby mode or enabled. | B |
| AGND | 7 | Possible device damage | A |
| COMP | 8 | The device can be unstable. | C |
| FB | 9 | Output voltage is out of regulation. | B |
| SS | 10 | During soft start, the SS pin pulled high. The device soft-start time is reduced to 0. High inrush current possible. No effect during operation | C |
| MODE | 11 | Hiccup mode protection is disabled and spread spectrum is enabled. No effect during operation | B |
| NC | 12, 15 | No effect. Normal operation | D |
| SW | 13, 14 | Output voltage is out of regulation. Output voltage is equal to the input voltage minus diode forward voltage drop. | 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 |
|---|---|---|---|---|
| PGND | 1 | VCC | VCC regulator short circuit. Device can shut down due to thermal shutdown. | B |
| VCC | 2 | BIAS | Potential device damage if BIAS voltage is greater 5.8 V | A |
| BIAS | 3 | PGOOD | Potential device damage if BIAS voltage is greater 18 V | A |
| PGOOD | 4 | RT | Loss of power-good functionality. Switching frequency is wrong. | B |
| RT | 5 | EN/UVLO/SYNC | EN pin voltage at enable threshold. The device is either disabled and in shutdown mode or in standby mode. | B |
| EN/UVLO/SYNC | 6 | AGND | EN stuck low. The device is disabled and in shutdown mode. | B |
| AGND | 7 | COMP | The device is out of regulation. The device is not switching. | B |
| COMP | 8 | FB | COMP and FB pin voltage are clamped to 1 V. The device is not switching and out of regulation. | B |
| FB | 9 | SS | COMP pin voltage clamped to 1 V. The device is not switching and out of regulation. | B |
| SS | 10 | MODE | MODE pin pulled low during read out. Hiccup mode protection is disabled and spread spectrum is disabled. | B |
| MODE | 11 | NC | No effect. Normal operation | D |
| NC | 12 | SW | No effect. Normal operation | D |
| SW | 13 | SW | No effect. Normal operation | D |
| SW | 14 | NC | No effect. Normal operation | D |
| NC | 15 | PGND | No effect. Normal operation | D |
| PGND | 16 | PGND | No effect. Normal operation | D |
Table 4-5 Pin FMA for Device Pins
Short-Circuited to BIAS
supply
| Pin Name | Pin No. | Description of Potential Failure Effect(s) | Failure Effect Class |
|---|---|---|---|
| PGND | 1, 16 | The device is unpowerered and not functional. Observe that the absolute maximum ratings for all pins of the device are met, otherwise device damage can be plausible. | A |
| VCC | 2 | Potential device damage if BIAS voltage is greater 5.8 V | A |
| BIAS | 3 | No effect. Normal operation | D |
| PGOOD | 4 | Potential device damage if BIAS voltage is greater 18 V | A |
| RT | 5 | Potential device damage if BIAS voltage is greater 3.8 V | A |
| EN/UVLO/SYNC | 6 | No effect. Normal operation | D |
| AGND | 7 | The device is unpowered. The device is not functional. Observe that the absolute maximum ratings for all pins of the device are met, otherwise device damage can be plausible. | A |
| COMP | 8 | Potential device damage | A |
| FB | 9 | Potential device damage if BIAS voltage is greater 4.0 V | A |
| SS | 10 | Potential device damage if BIAS voltage is greater 3.8 V | A |
| MODE | 11 | Potential device damage if BIAS voltage is greater 3.8 V | A |
| NC | 12, 15 | No effect. Normal operation | D |
| SW | 13, 14 | Inductor out of regulation loop. Device is not functional. | B |