SFFS533 October   2022 LM51231-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 LM51231-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
ClassFailure Effects
APotential device damage that affects functionality.
BNo device damage, but loss of functionality.
CNo device damage, but performance degradation.
DNo device damage, no impact to functionality or performance.

Figure 4-1 shows the LM51231-Q1 pin diagram. For a detailed description of the device pins, see the Pin Configuration and Functions section in the LM51231-Q1 data sheet.

Figure 4-1 Pin Diagram

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 LM51231-Q1 data sheet.
  • For the analysis, the typical application as shown in the Typical Application section of the LM51231-Q1 is used
  • VSUPPLY = VBIAS = 12 V
  • VOUT = 24 V
Table 4-2 Pin FMA for Device Pins Short-Circuited to Ground
Pin Name Pin No. Description of Potential Failure Effects Failure Effect Class
CSP 1 CSP Pin can be damaged due to the differential voltage exceeds the 0.3V abs max rating. A
CSN 2 CSN Pin can be damaged due to the differential voltage exceeds the 0.3V abs max rating. A
VOUT/SENSE 3 VOUT out of regulation, possible over charge of the output voltage A
PGOOD 4 Correct output voltage, but loss of power-good functionality. C
HO 5 High-side driver can be damaged when SW voltage rises A
SW 6 No energy transferred from input to output B
HB 7 Can be damaged when SW voltage rises A
BIAS 8 Device unpowered and therefore not functional. B
VCC 9 Loss of VCC regulation, no switching B
PGND 10 No effect. D
LO 11 VOUT out of regulation. LO stops switching. B
MODE 12 Diode emulation mode is activated. No effect in case the device is configured for diode emulation mode (MODE = GND). C
UVLO/EN 13 Device is disabled. B
SYNC/DITHER/VH 14 External Clock Synchronization is disabled. Spread Spectrum is disabled. VCC is not hold when EN = GND. No effect in case External Clock Synchronization and Spread Spectrum are disabled as well as the VCC hold function is disabled (SYNC/DITHER/VH = GND). C
RT 15 Maximum switching frequency much greater than 2.21 MHz C
VREF/RANGE 16 No switching. Target output voltage is 0 V B
SS 17 Device does not start, no switching B
TRK 18 VOUT out of regulation, no switching B
AGND 19 No effect. D
COMP 20 VOUT out of regulation, not switching. B
Table 4-3 Pin FMA for Device Pins Open-Circuited
Pin Name Pin No. Description of Potential Failure Effects Failure Effect Class
CSP 1 Loss of current sense signal. B
CSN 2 Loss of current sense signal. B
VOUT/SENSE 3 VOUT out of regulation, possible over charge of the output voltage A
PGOOD 4 Correct output voltage, but loss of power-good functionality. C
HO 5 Loss of high side driver. Operating with sync FET body diode conducting. C
SW 6 Loss of high side driver. Operating with sync FET body diode conducting. C
HB 7 Loss of boot voltage and hence high side driver. Operating with sync FET body diode conducting. C
BIAS 8 Device unpowered and therefore not functional. B
VCC 9 No stable VCC to sustain normal operation B
PGND 10 Possible device damage. A
LO 11 Low-side MOSFET never switched. B
MODE 12 No effect if diode emulation mode is active, otherwise diode emulation mode is activated. C
UVLO/EN 13 Device is disabled. B
SYNC/DITHER/VH 14 Loss of VCC hold up functionality C
RT 15 Minimum frequency is set. C
VREF/RANGE 16 VOUT out of regulation, B
SS 17 Small soft-start time. Normal operation after C
TRK 18 VOUT out of regulation B
AGND 19 Possible device damage. A
COMP 20 Device may be unstable. C
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
CSP 1 CSN Loss of current sense information. Circuit possibly unstable C
CSN 2 VOUT/SENSE Possible damage. Exceeds absolute maximum voltage rating A
VOUT/SENSE 3 PGOOD Loss of VOUT feedback. Possibly unstable operation B
PGOOD 4 HO No damage, loss of PGOOD function B
HO 5 SW Loss of high side driver. Operating with sync FET body diode conducting. B
SW 6 HB Loss of boot voltage and hence high side driver. Operating with sync FET body diode conducting. B
HB 7 BIAS Possible damage. HB exceeds absolute maximum voltage rating A
BIAS 8 VCC Possible damage to VCC if BIAS is above the absolute maximum voltage rating of VCC, otherwise no damage A
VCC 9 PGND No VCC rail, no switching B
PGND 10 LO LO never turns on. Switching never happens B
LO 11 MODE Switching mode toggles with every switching cycle C
MODE 12 UVLO/EN Switching mode set by the UVLO/EN pin voltage B
UVLO/EN 13 SYNC/DITHER/VH SYNC/DITHER/VH setting set by the UVLO/EN pin B
SYNC/DITHER/VH 14 RT Can exceed the RT absolute maximum voltage A
RT 15 VREF/RANGE Switching frequency will not be correct C
VREF/RANGE 16 SS Small soft-start time C
SS 17 TRK TRK > 1.2V will stop any switching on the controller. B
TRK 18 AGND VOUT out of regulation, no switching B
AGND 19 COMP VOUT out of regulation, not switching. B
COMP 20 CSP Possible damage. Exceeds absolute maximum voltage rating of COMP A
Table 4-5 Pin FMA for Device Pins Short-Circuited to 12 V supply
Pin Name Pin No. Description of Potential Failure Effects Failure Effect Class
CSP 1 Normal operation D
CSN 2 Loss of current sense signal. Circuit possibly unstable C
VOUT/SENSE 3 VOUT out of regulation B
PGOOD 4 Loss of PGOOD functionality C
HO 5 HO pin can exceed the HO to SW absolute maximum voltage rating A
SW 6 No energy is transferred from input to output B
HB 7 HB exceeds HB to SW absolute maximum voltage rating A
BIAS 8 Normal operation D
VCC 9 VCC exceeds absolute maximum voltage rating A
PGND 10 Possible damage A
LO 11 Possible damage. Exceeds absolute maximum voltage rating A
MODE 12 Possible damage. Exceeds absolute maximum voltage rating A
UVLO/EN 13 No UVLO functionality C
SYNC/DITHER/VH 14 Possible damage. Exceeds absolute maximum voltage rating A
RT 15 Possible damage. Exceeds absolute maximum voltage rating A
VREF/RANGE 16 Possible damage. Exceeds absolute maximum voltage rating A
SS 17 Possible damage. Exceeds absolute maximum voltage rating A
TRK 18 Possible damage. Exceeds absolute maximum voltage rating A
AGND 19 Possible damage. Exceeds absolute maximum voltage rating A
COMP 20 Possible damage. Exceeds absolute maximum voltage rating A