SFFSA01 September   2024 LM70660 , LM706A0

 

  1.   1
  2.   Trademarks
  3. 1Overview
  4. 2Functional Safety Failure In Time (FIT) Rates
  5. 3Failure Mode Distribution (FMD)
  6. 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 LM706A0 and LM70660. The failure modes covered in this document include the typical pin-by-pin failure scenarios:

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 LM706A0 and LM70660 pin diagram. For a detailed description of the device pins, refer to the Pin Configuration and Functions section in the LM706A0 and LM70660 data sheet.

LM706A0 LM70660 Pin Diagram 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 EffectsFailure Effect Class
VIN1-3VOUT = 0VB
CBOOT4VOUT = 0V, VCC regulator loaded to Current Limit B
SW5VOUT = 0V, high-side FET shorted from VIN to GND A
BIAS6VOUT = expected VOUT, internal VCC regulator provides bias voltageD
PGOOD7VOUT = expected VOUTD
PFM/SYNC 8 VOUT = expected VOUT, no synchronization possible and is in FPWM mode C
EN/UVLO 9 VOUT = 0V, enters shutdown mode B
NC 10 N/A D
ISNS+ 11 VOUT = 0V, HO damaged A
VOUT 12 Current limit reached, VOUT = 0V and enters hiccup mode B
CONFIG 13 Expected VOUT, spread spectrum and multiphase mode disabled C
RT 14 VOUT = expected VOUT, FSW at maximum causing maximum power dissipation C
EXTCOMP 15 VOUT = 0V B
FB16 Internal FB MODE, VOUT = expected VOUTD
External FB MODE VOUT = VINA
AGND17AGND is GND, VOUT = expected VOUTD
VDDA18VOUT = 0V, no switching, loaded VCC outputB
VCC19VOUT = 0V, no switching, loaded VCC outputB
SW20-22VOUT = 0V, high-side FET shorted from VIN to GNDA
PGND23-26 PGND is GND, VOUT = expected VOUTD
VIN27-29VOUT = 0VB
Table 4-3 Pin FMA for Device Pins Open-Circuited
Pin NamePin No.Description of Potential Failure EffectsFailure Effect Class
VIN1-3VOUT = expected VOUT, part works through VIN on pins 27-29 D
CBOOT4VOUT = 0VB
SW5VOUT = expected VOUT, part works through SW on pins 20-22D
BIAS6VCC working off internal VCC regulatorD
PGOOD7If in single mode, PGOOD has no effect on operationD
If in multiphase primary mode, the secondary detects no clock input and shuts down B
PFM/SYNC8VOUT = expected VOUTC
EN/UVLO9Device state in indeterminateB
NC10VOUT = expected VOUTD
ISNS+11OPEN current sense pin blocks current limit and causes VOUT oscillationsA
VOUT12VOUT = 0VB
CONFIG13CONFIG is used during start up, VOUT = expected VOUT D
RT14RT regulates to 500mV but internal oscillator does not functionB
EXTCOMP15VOUT oscillates, if VOUT oscillates to VIN, damage can occur if VIN > 60VA
FB16If external FB mode, VOUT is indeterminateB
If Internal FB mode, VOUT operates normally D
AGND17VOUT is indeterminateD
VDDA18Poor noise immunityD
VCC19VOUT = expected VOUT until damage occursA
SW20-22VOUT = 0VB
PGND23-26VOUT is indeterminateB
VIN27-29VOUT = expected VOUT, part works through VIN on pins 1-3D
Table 4-4 Pin FMA for Device Pins Short-Circuited to Adjacent Pin
Pin NamePin No.Shorted toDescription of Potential Failure EffectsFailure Effect Class
NC1NCNo impactD
NC2CNFGNo impactD
CNFG3RTVOUT = expected VOUT with erratic switchingB
RT4EXTCOMPCOMP cannot regulate down due to clamping by internal RTB
EXTCOMP5FBExternal FB mode: COMP regulates to 0.8V and output is unregulated,

VOUT = indeterminate

B
Internal FB mode: COMP rises up to VDDA, VOUT = VINA
FB6AGNDExternal FB mode: VOUT = VINA
Internal FB mode: VOUT = expected VOUTD
AGND7VDDAVDDA is grounded, VOUT = 0VB
VDDA8VCCVOUT = expected VOUTD
VCC9PGNDVCC is grounded, VOUT = 0VB
PGND10LOVOUT = 0V, VCC is loaded by the LO driver B
LO11VINVOUT = 0V, the driver is damaged if VIN > 6.5V A
VIN12HOVOUT = VINA
HO13SWVOUT = 0VB
SW14CBOOTVOUT = 0VB
CBOOT15VCCXVOUT < 5VA
VCCX16PGPG pulldown can damage, VOUT = expected VOUTA
PG17PFM/SYNCVOUT = expected VOUTC
PFM/SYNC18ENVOUT = expected VOUTA
EN19ISNS+

EN is high-voltage rated, VOUT = expected VOUT, if VOUT > 1V

If VOUT < 1V, the device is disabled

B
ISNS+20VOUT

Current limit is disabled since the current limit resistor is shorted

VOUT cannot regulate since current mode feedback is shorted

A
VOUT21NCNo impactD
NC22NCNo impactD
NC23NCNo impactD
NC24NCNo impactD
Table 4-5 Pin FMA for Device Pins Short-Circuited to VIN
Pin NamePin No.Description of Potential Failure EffectsFailure Effect Class
VIN1-3No impactD
CBOOT4If VIN < 6.5V, VOUT = expected VOUT, erratic switchingC
If VIN > 6.5V, exceeds max ratings and CBOOT pin is damaged, HO bias damage A
SW5VOUT=VIN, excess current from VIN through low-side FETB
BIAS6If VIN < 40V, VOUT = expected VOUTD
If VIN > 40V, exceeds maximum ratings and the pin VCC is damaged, VOUT = 0V A
PGOOD7If VIN < 6.5V, VOUT = expected, PG possibly forced high exceeding the PG pulldown SOAB
If VIN > 6.5V, exceeds maximum ratings and pin PG is destroyed, VOUT = expected VOUT B
PFM/SYNC8If VIN < 6.5V, VOUT = expected VOUTD
If VIN > 6.5V, exceeds maximum ratings and pin PFM/SYNC is destroyed

VOUT = expected VOUT

D
EN/UVLO9Part is always be enabled, VOUT = expected VOUTC
NC 10 No impact D
ISNS+11if VIN < 6.5V, VOUT = VINB
If VIN > 60V, exceeds maximum ratings and pin ISNS+ is damaged. VOUT = VINA
VOUT12If VIN < 6.5V, VOUT = VIND
If VIN > 60V, exceeds maximum ratings and pin VOUT is damaged, VOUT = VINA
CONFIG13If VIN < 6.5V, VOUT = expected VOUTB
If VIN > 6.5V, exceeds maximum ratings and pin CONFIG is destroyed A
RT14If VIN < 6.5V, VOUT= 0V as frequency goes to 0HzB
If VIN > 6.5V, exceeds maximum ratings and pin RT is destroyedA
EXTCOMP15This brings VCC up to VIN, VOUT = VINA
FB16If VIN > 16V (fixed version) or 5.5V (adjustable version) damage occurs,VOUT = 0VB
AGND17VIN shorts to GND, VOUT = 0VA
VDDA18If VIN < 6.5V, no impactD
If VIN > 6.5V, exceeds maximum ratings and pin VDDA is damagedA
VCC19If VIN < 12V, no impactD
If VIN > 12V, exceeds maximum ratings and pin VCC is damagedA
SW20-22VOUT = VIN, excess current from VIN through low-side FETB
PGND23-26VIN shorts to GND. VOUT = 0VA
VIN27-29No impactD