SFFSA10 October 2024 LMR51635
4 Pin Failure Mode Analysis (Pin FMA)
This section provides a failure mode analysis (FMA) for the pins of the LMR51625 and LMR51635. 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 VIN (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. |
Following are the assumptions of use and the device configuration assumed for the pin FMA in this section:
- Device is used within the Recommended Operating Conditions and the Absolute Maximum Ratings found in the appropriate device data sheet.
- Configuration is as shown in the Example Application Circuit found in the appropriate device data sheet.
Figure 4-1 shows the LMR51625 and LMR51635 pin diagram for the SOT-23 package. For a detailed description of the device pins please refer to the Pin Configuration and Functions section in the appropriate device data sheet.
Figure 4-1 Pin DiagramTable 4-2 Pin FMA for Device Pins Short-Circuited to Ground
| Pin Name | Pin No. | Description of Potential Failure Effects | Failure Effect Class |
|---|---|---|---|
| FB | 1 | The regulator operates at maximum duty cycle. Output voltage rises approximately to the input voltage (VIN) level. Damage to customer load and output stage components are possible. No effect on device. | B |
| EN | 2 | Loss of ENABLE functionality. Device remains in shutdown mode. | B |
| VIN | 3 | Device does not operate. No output voltage is generated. Output capacitors discharge through the input short. A large current reversal can damage the device. | A |
| GND | 4 | Normal operation. | D |
| SW | 5 | Damage to internal FET. | A |
| CB | 6 | No output voltage. | B |
Table 4-3 Pin FMA for Device Pins Open-Circuited
| Pin Name | Pin No. | Description of Potential Failure Effects | Failure Effect Class |
|---|---|---|---|
| FB | 1 | VOUT is higher than the programmed output voltage. | B |
| EN | 2 | Loss of ENABLE functionality. Erratic operation; loss of regulation is probable. | B |
| VIN | 3 | No output voltage. | B |
| GND | 4 | VOUT can be abnormal due to switching noise on analog circuits. | B |
| SW | 5 | No output voltage. | B |
| CB | 6 | No output voltage. | 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 |
|---|---|---|---|---|
| FB | 1 | EN | If EN exceeds 5.5V, damage occurs. No output voltage. | A |
| EN | 2 | VIN | No damage to device. Loss of ENABLE functionality. | B |
| VIN | 3 | GND | Device does not operate. No output voltage is generated. Output capacitors discharge through the input short. A large current reversal can damage the device. | A |
| GND | 4 | SW | Damage to internal FET. | A |
| SW | 5 | CB | No output voltage. Damage to internal FET. | B |
| CB | 6 | FB | If CB exceeds 5.5V, damage occurs. No output voltage. | A |
Table 4-5 Pin FMA for Device Pins Short-Circuited to VIN
| Pin Name | Pin No. | Description of Potential Failure Effects | Failure Effect Class |
|---|---|---|---|
| FB | 1 | If VIN exceeds 5.5V, damage occurs. No output voltage. | A |
| EN | 2 | No damage to device. Loss of ENABLE functionality. | B |
| VIN | 3 | No effect. | D |
| GND | 4 | No output voltage. Damage to other pins referred to GND. | A |
| SW | 5 | Damage to low-side MOSFET. | A |
| CB | 6 | No output voltage. CB pin ESD clamp runs current to destruction. | A |