SFFS188 September   2021 LM64460-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 LM64460-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 LM64460-Q1 pin diagram. For a detailed description of the device pins please refer to the Pin Configuration and Functions section in the LM64460-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:

Table 4-2 Pin FMA for Device Pins Short-Circuited to Ground
Pin NamePin No.Description of Potential Failure Effect(s)Failure Effect Class
CBOOT1VOUT = 0 VB
NC 2 No effect D
BIAS 3 Normal Operation, Chip power now from VIN causing decreased efficiency C
VCC 4 VOUT = 0 V B
FB 5

VOUT >> than programmed output voltage

 B
PGOOD 6

PGOOD not valid signal. No other changes to chip performance. VOUT in regulation

 C
MODE/SYNC 7 AUTO mode operation only, VOUT normal C
EN8VOUT = 0 VB
NC 9 No effect D
VIN2 10 VOUT = 0 V B
NC 11 No effect D
PGND2 12 No effect D
NC 13 No effect D
SW1 14 Damage to HS FET A
SW2 15 Damage to HS FET A
SW3 16 Damage to HS FET A
NC 17 No effect D
PGND1 18 No effect D
NC 19 No effect D
VIN1 20 VOUT = 0 V B
NC 21 No effect D
SW4 22 Damage to HS FET A
GNDDAPNo effectD
Table 4-3 Pin FMA for Device Pins Open-Circuited
Pin NamePin No.Description of Potential Failure Effect(s)Failure Effect Class
CBOOT1VOUT = 0 VB
NC2No effectD
BIAS 3 Normal Operation, Chip power now from VIN causing decreased efficiency C
VCC 4

VCC output will be unstable and can increase above 5.5 V rating of VCC pin

 A
FB 5

VOUT >> than programmed output voltage.

 B
PGOOD 6

PGOOD not valid signal. VOUT in regulation

 C
MODE/SYNC 7 AUTO vs FPWM and spread spectrum operation undetermined, VOUT normal C
EN 8 Unpredictable operation B
NC 9 No effect D
VIN2 10

VOUT normal. Current loop will be affected, potentially affecting noise/jitter/EMI/reliability

 C
NC 11 No effect D
PGND2 12 VOUT normal. Current loop will be affected, potentially affecting noise/jitter/EMI/reliability C
NC 13 No effect D
SW1 14 No effect, 2 SW pins sufficient D
SW2 15 No effect, 2 SW pins sufficient D
SW3 16 No effect, 2 SW pins sufficient D
NC 17 No effect D
PGND1 18

VOUT normal. Current loop will be affected, potentially affecting noise/jitter/EMI/reliability

 C
NC 19 No effect D
VIN1 20

VOUT normal. Current loop will be affected, potentially affecting noise/jitter/EMI/reliability

 C
NC 21 No effect D
SW4 22 VOUT = 0 V, Needed for CBOOT B
GNDDAPLoad regulation degraded, thermal impedance impacted 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
CBOOT1NCNo effectD
NC2BIASNo effectD
BIAS 3 VCC

VCC ESD clamp damaged if BIAS > 5 V

 A
VCC 4 FB VOUT = 0 V B
FB 5 PGOOD VOUT can become >> than programmed output voltage B
PGOOD 6 MODE/SYNC FPWM mode operation only, VOUT normal C
MODE/SYNC 7 EN FPWM mode operation only, VOUT normal C
EN 8 NC No effect D
NC 9 VIN2 No effect D
VIN2 10 NC No effect D
NC 11 PGND2 No effect D
PGND2 12 NC No effect D
NC 13 SW1 No effect D
SW1 14 SW2 No effect D
SW2 15 SW3 No effect D
SW3 16 NC No effect D
NC 17 PGND1 No effect D
PGND1 18 NC No effect D
NC 19 VIN1 No effect D
VIN1 20 NC No effect D
NC 21 SW4 No effect D
SW4 22 CBOOT VOUT = 0 V B
GNDDAPAnyOther pin is shorted to ground, see Table 4-2
Table 4-5 Pin FMA for Device Pins Short-Circuited to supply
Pin NamePin No.Description of Potential Failure Effect(s)Failure Effect Class
CBOOT1

VOUT = 0 V. CBOOT ESD clamp will run current to destruction.

A
NC2No effectD
BIAS 3

If VIN exceeds 16 V damage will occur. If below, normal operation

 A
VCC 4

If VIN exceeds 5.5 V damage will occur.

 A
FB 5

If VIN exceeds 16V damage will occur. VOUT = 0 V

 A
PGOOD 6

VOUT = 0 V. PGOOD ESD clamp will run current to destruction

 A
MODE/SYNC 7 Will run in FPWM mode C
EN 8 VOUT normal D
NC 9 No effect D
VIN2 10 No effect D
NC 11 No effect D
PGND2 12 VOUT = 0 V B
NC 13 No effect D
SW1 14 Damage to LS FET A
SW2 15 Damage to LS FET A
SW3 16 Damage to LS FET A
NC 17 No effect D
PGND1 18 VOUT = 0 V B
NC 19 No effect D
VIN1 20 No effect D
NC 21 No effect D
SW4 22 Damage to LS FET A
GNDDAP

VOUT = 0 V.

B