SFFS307 November   2021 LM5123-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)

Pin Failure Mode Analysis (Pin FMA)

This section provides a failure mode analysis (FMA) for the pins of the LM5123-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 LM5123-Q1 pin diagram. For a detailed description of the device pins, see the Pin Configuration and Functions section in the LM5123-Q1 data sheet.

GUID-20200807-CA0I-FKCN-H5CH-DXTSMZVZ8HQC-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:

  • Device used within the Recommended Operation Conditions and the Absolute Maximum Ratings found in the LM5123-Q1 data sheet.
  • For the analysis, the typical application as shown in the Typical Application section of the LM5123-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 Effect(s) Failure Effect Class
CSP 1 The CSP pin can be damaged if the differential voltage exceeds the 0.3-V abs max rating. A
CSN 2 The CSN pin can be damaged if the differential voltage exceeds the 0.3-V abs max rating. A
VOUT/SENSE 3 VOUT is out of regulation. Possible overcharge of the output voltage A
PGOOD 4 Correct output voltage, but loss of power-good functionality B
HO 5 High-side driver can be damaged when SW voltage rises. A
SW 6 No energy is transferred from input to output. B
HB 7 The HB pin can be damaged when SW voltage rises. A
BIAS 8 The device is unpowered and, therefore, not functional. B
VCC 9 Loss of VCC regulation and there is no switching B
PGND 10 No effect D
LO 11 VOUT is 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 The device is disabled. B
SYNC/DITHER/VH/CP 14 External clock synchronization is disabled. Spread spectrum is disabled. VCC is not held when EN = GND and the high-side switch cannot turn on 100% during bypass operation. No effect in case external clock synchronization and spread spectrum are disabled and the VCC hold function and high-side switch turn on 100% in bypass mode function is disabled (SYNC/DITHER/VH/CP = GND). C
RT 15 Maximum switching frequency is 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 and there is no switching. B
TRK 18 VOUT out of regulation and there is no switching. B
AGND 19 No effect D
COMP 20 VOUT out of regulation and is not switching. B
Table 4-3 Pin FMA for Device Pins Open-Circuited
Pin NamePin No.Description of Potential Failure Effect(s)Failure Effect Class
CSP1Loss of current sense signalB
CSN2Loss of current sense signalB
VOUT/SENSE3VOUT out of regulation and there is a possible overcharge of the output voltage.A
PGOOD 4 Correct output voltage, but loss of power-good functionality B
HO 5 Loss of the high-side driver. Operating with sync FET body diode conducting C
SW 6 Loss of the high-side driver. Operating with sync FET body diode conducting C
HB 7 Loss of boot voltage and hence, the high-side driver. Operating with sync FET body diode conducting C
BIAS 8 Device is 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 is never switched. B
MODE 12 No effect if skip mode is active, otherwise skip mode is activated. C
UVLO/EN 13 Device is disabled. B
SYNC/DITHER/VH/CP 14 Loss of holdup functionality and charge-pump functionality C
RT 15 Minimum frequency is set. C
VREF/RANGE 16 VOUT is out of regulation. B
SS 17 Small soft-start time. Normal operation after start-up C
TRK 18 VOUT out of regulation B
AGND 19 Possible device damage A
COMP 20 Device can be unstable. C
Table 4-4 Pin FMA for Device Pins Short-Circuited to Adjacent Pin
Pin NamePin No.Shorted toDescription of Potential Failure Effect(s)Failure Effect Class
CSP1CSNLoss of current sense information. Circuit can be unstable.C
CSN2VOUT/SENSEPossible damage. Exceeds absolute maximum voltage ratingA
VOUT/SENSE3 PGOOD Loss of VOUT feedback. Possibly unstable operationB
PGOOD 4 HO No damage and loss of PGOOD function B
HO 5 SW Loss of the high-side driver. Operating with sync FET body diode conducting B
SW 6 HB Loss of boot voltage and hence, the high-side driver. Operating with sync FET body diode conducting B
HB 7 BIAS Possible damage. HB exceeds the 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 and there is 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 is set by the UVLO/EN pin voltage. B
UVLO/EN 13 SYNC/DITHER/VH/CP SYNC/DITHER/VH/CP setting set by the UVLO/EN pin. B
SYNC/DITHER/VH/CP 14 RT Possible damage. 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 > 1.2 V stops any switching on the controller. B
TRK 18 AGND VOUT is out of regulation and there is no switching. B
AGND 19 COMP VOUT is out of regulation and is 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 NamePin No.Description of Potential Failure Effect(s)Failure Effect Class
CSP1Normal operationD
CSN2Loss of current sense signal. Circuit can be unstable.C
VOUT/SENSE3VOUT is out of regulation.B
PGOOD 4 Loss of PGOOD functionality B
HO 5 The 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/CP 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