SFFS073 September   2021 LM5158-Q1 , LM51581-Q1

 

  1.   Trademarks
  2. 1Overview
  3. 2Functional Safety Failure In Time (FIT) Rates
  4. 3Failure Mode Distribution (FMD)
  5. 4Pin Failure Mode Analysis (Pin FMA)

4 Pin Failure Mode Analysis (Pin FMA)

This section provides a Failure Mode Analysis (FMA) for the pins of the LM5158-Q1 and LM51581-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 LM5158-Q1 and LM51581-Q1 pin diagram. For a detailed description of the device pins please refer to the Pin Configuration and Functions section in the LM5158-Q1 and LM51581-Q1 data sheet.

GUID-20210304-CA0I-C6SK-LDTG-RCZCDFTFDBLR-low.gif Figure 4-1 Pin Diagram

Following are the assumptions of use and the device configuration assumed for the pin FMA in this section:

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. Device may shut down due to thermal shut down. B
BIAS 3 Device unpowered. 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. Device may be unstable. B
EN/UVLO/SYNC 6 EN stuck low. Device disabled and in shutdown mode. B
AGND 7 No effect. Normal operation D
COMP 8 Device out of regulation. 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 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 Device unpowered. 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 may be in shutdown or standby mode or enabled. B
AGND 7 Possible device damage A
COMP 8 Device may 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 may 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. Device is either disabled and in shutdown mode or in standby mode. B
EN/UVLO/SYNC 6 AGND EN stuck low. Device is disabled and in shutdown mode. B
AGND 7 COMP Device out of regulation. Device is not switching. B
COMP 8 FB COMP and FB pin voltage clamped to 1 V. Device is not switching and out of regulation. B
FB 9 SS COMP pin voltage clamped to 1 V. 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 Device unpowered. Device not functional. Observe that the absolute maximum ratings for all pins of the device are met, otherwise device damage may 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 Device unpowered. Device is not functional. Observe that the absolute maximum ratings for all pins of the device are met, otherwise device damage may 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