SFFS183 March   2022 LMR43610 , LMR43610-Q1 , LMR43620 , LMR43620-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 LMR436x0 and LMR436x0-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 LMR436x0 and LMR436x0-Q1 pin diagram. For a detailed description of the device pins please refer to the Pin Configuration and Functions section in the LMR436x0 and LMR436x0-Q1 data sheet.

GUID-20201001-CA0I-B0KM-HCC8-263DVBP3KKSQ-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 NamePin No.Description of Potential Failure Effect(s)Failure Effect Class
RT or MODE/SYNC1The switching frequency is 2.2 MHz.D
PGOOD2When not in use, this pin can be left grounded (PGOOD is not a valid signal and VOUT is normal).D
EN/UVLO3VOUT = 0 V (Enable is off and functionality is halted.)D
VIN4VOUT = 0 VB
SW5Damage to HSFET A
BOOT6VOUT = 0 V. HS does not turn on.B
VCC7VOUT = 0 VB
VOUT/BIAS or FB8When in adjustable output mode, VOUT approaches VIN. When in fixed output mode, VOUT = 0 V.B
GND9VOUT is normal.D
Table 4-3 Pin FMA for Device Pins Open-Circuited
Pin NamePin No.Description of Potential Failure Effect(s)Failure Effect Class
RT or MODE/SYNC1If it is an RT part, frequency is not defined. If it is a MODE/SYNC part, then the part can go back and forth between FPWM/PFM. The part is up and functional. C
PGOOD2When not in use, this pin can be left open (PGOOD is not a valid signal and VOUT is normal). D
EN/UVLO3Pin cannot be left floating. B
VIN4VOUT = 0 V B
SW5VOUT = 0 V B
BOOT6VOUT = 0. HS does not turn on.B
VCC7VCC output is unstable and can increase above 5.5 V.A
VOUT/BIAS or FB8VOUT approaches VIN.C
GND9VOUT can be abnormal, as reference voltage is not fixed.C
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
RT or MODE/SYNC 1 PGOOD If PGOOD is high, and < 5.5 V, FSW = 1 MHz. If PGOOD is low, FSW = 2.2 MHz. With PGOOD absolute maximum rating being 20 V, RT ESD damages if PG goes to 20 V. A
PGOOD 2 EN/UVLO If EN/UVLO > 20 V, it damages devices connected to the PGOOD pin. A
EN/UVLO 3 VIN VOUT is normal (Enable is on and all other blocks work). D
VIN 4 SW Damage to LSFET A
SW 5 BOOT VOUT = 0 V, HS does not turn on and there is no CBOOT. B
BOOT 6 VCC Damage occurs and there is a break to the VCC pin. A
VCC 7 VOUT/BIAS or FB Does not work, but no damage occurs. B
VOUT/BIAS or FB 8 GND When in adjustable output mode, VOUT approaches VIN. When in fixed output mode, VOUT = 0 V. B
GND 9 RT or MODE/SYNC VOUT is normal if the RT/MODE/SYNC pin is low, otherwise not functional. B
Table 4-5 Pin FMA for Device Pins Short-Circuited to supply
Pin Name Pin No. Description of Potential Failure Effect(s) Failure Effect Class
RT or MODE/SYNC 1 If VIN > 5.5 V, damage occurs. If VIN < 5.5 V, switching frequency is 1 MHz. A
PGOOD 2 If VIN > 20 V, it damages PGOOD. A
EN/UVLO 3 VOUT is normal (Enable is on, all other blocks will work). D
VIN 4 VOUT is normal. D
SW 5 Damage to LSFET A
BOOT 6 Damage occurs and BOOT ESD clamp is damaged. A
VCC 7 If VIN > 5.5 V, damage occurs. A
VOUT/BIAS or FB 8 If VIN > 16 V, damage occurs. A
GND 9 VOUT = 0 V B