SFFS313 November   2021 UCC28781-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 UCC28781-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 UCC28781-Q1 pin diagram. For a detailed description of the device pins, see the Pin Configuration and Functions section in the UCC28781-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:

  • IC is set up according to the typical application circuit shown in UCC28781-Q1 datasheet Figure 11-1
  • VDD pin is considered as the supply pin
Table 4-2 Pin FMA for Device Pins Short-Circuited to Ground
Pin NamePin No.Description of Potential Failure Effect(s)Failure Effect Class
FLT1IC enters fault mode, no PWML or PWMH output.B
RTZ 2 Pin short protection. IC tries to restart. Converter has no output. B
RDM 3 Pin short protection. IC tries to restart. Converter has no output. B
IPC 4 No impact on operation. Converter operates with slightly lower efficiency at light load. C
BUR 5 Burst mode threshold sets to minimum. Light load efficiency will be worse. C
FB 6 Converter delivers minimum power. PWML with minimum on time. No PWMH output. B
REF 7 No PWML or PWMH output. Converter has no output. B
AGND 8 No effect. D
CS 9 Controller enters CS pin short protection. IC tries to restart. Converter has no output. B
RUN 10 VREF overload. IC shuts down and retries. B
PGND 11 No effect. D
PWML 12 PWML has no output. IC protects and retries after UVLO. B
S13 13 No PWML or PWMH output. Converter has no output. B
P13 14 No PWML or PWMH output. Converter has no output. B
PWMH 15 VREF overload. IC shuts down and retries. B
SWS 16 IC can't start up. B
XCD 17 XCD function is lost. Possible damage on the line sensing device. B
XCD 18 XCD function is lost. Possible damage on the line sensing device. B
VDD 19 No PWML or PWMH output. Converter has no output. B
GTP1 20 No effect. D
GTP2 21 No effect. D
GTP322No effect.D
VS23Controller enters brownout protection. IC enters UVLO mode and retries.B
SET 24 Configure to GaN MOSFET. Either no impact, or converter operates with worse efficiency. C
Table 4-3 Pin FMA for Device Pins Open-Circuited
Pin NamePin No.Description of Potential Failure Effect(s)Failure Effect Class
FLT1No impact on operation. IC loses FLT pin fault protection function.C
RTZ2RTZ pin open pin protection. IC tries to restart. Converter has no output.B
RDM3RDM pin open pin protection. IC tries to restart. Converter has no output.B
IPC 4 No impact on operation. Converter operates with slightly higher efficiency at light load. Converter might have audible noise. C
BUR 5 Burst level sets to highest. Burst mode threshold and the light load efficiency will be different. C
FB 6 OVP is triggered. IC shuts down and retries. B
REF 7 No effect. IC might shutdown due to the noise coupling into REF pin. C
AGND 8 Behavior can be unpredictable. IC damage is possible. A
CS 9 CS pin open protection. IC enters UVLO mode and retries. B
RUN 10 No effect. D
PGND 11 Behavior can be unpredictable. IC damage is possible. A
PWML 12 Converter has no output. B
S13 13 No effect. D
P13 14 P13 pin open pin protection. B
PWMH 15 No SR driver signal, converter operates with less efficiency. Power stage might get damaged. C
SWS 16 IC does not start. B
XCD 17 No effect. D
XCD 18 No effect. D
VDD 19 IC is not biased. No PWML or PWMH output. B
GTP1 20 No effect. D
GTP2 21 No effect. D
GTP3 22 No effect. D
VS 23 IC enters protection mode, shuts down and retries. B
SET 24 IC sets to Si MOSFET mode. Either no impact or converter operates with worse efficiency 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
FLT1RTZRTZ pin setting is wrong. Converter efficiency will be lower. RTZ pin short protection is possible. IC loses FLT pin fault protection function.C
RTZ2RDMRDM pin open protection. IC tries to restart. Converter has no output.B
RDM3IPCRDM pin short protection. IC tries to restart. Converter has no output.B
IPC 4 BUR Burst level is lower than designed. Wrong burst threshold. Converter light load efficiency might be worse. C
BUR 5 FB Burst level is higher than designed. Wrong burst threshold. Converter light load efficiency might be different. The converter might reduce its maximum power handling capability. C
FB 6 N/A N/A N/A
REF 7 AGND No PWML or PWMH output. Converter has no output. B
AGND 8 CS IC enters CS pin short protection. IC enters UVLO mode and retries. B
CS 9 RUN IC shuts down and retries. Converter has no output. B
RUN 10 PGND VREF overload protection. IC shuts down and retries. B
PGND 11 PWML VREF overload protection. IC shuts down and retries. B
PWML 12 N/A N/A N/A
S13 13 P13 No impact. D
P13 14 PWMH PWMH stays high. Possible IC and power stage damage. A
PWMH 15 SWS IC can't start up. B
SWS 16 XCD XCD function is lost. C
XCD 17 XCD No effect. D
XCD 18 N/A N/A N/A
VDD 19 GTP1 IC is not biased. No PWML or PWMH output. B
GTP1 20 GTP2 No effect. D
GTP2 21 GTP3 No effect. D
GTP3 22 VS IC can't start up. B
VS 23 SET IC can't start up. B
SET 24 N/A N/A N/A
Table 4-5 Pin FMA for Device Pins Short-Circuited to supply
Pin NamePin No.Description of Potential Failure Effect(s)Failure Effect Class
FLT1IC enters protection mode. Possible IC damage.A
RTZ2IC shuts down and retries. Possible IC damage.A
RDM3IC shuts down and retries. Possible IC damage.A
IPC 4 IC operates with higher peak current at light load mode. Possible IC damage. A
BUR 5 IC shuts down and retries. Possible IC damage. A
FB 6 IC triggers OVP protection. Possible IC damage. A
REF 7 IC enters protection mode. Possible IC damage. A
AGND 8 IC is not biased. No PWML or PWMH output. Converter has no output B
CS 9 IC enters protection mode. Possible IC damage. A
RUN 10 IC enters protection mode. Possible IC damage. A
PGND 11 IC is not biased. No PWML or PWMH output. Converter has no output. B
PWML 12 IC can't start up. B
S13 13 IC can't start up. B
P13 14 IC can't start up. B
PWMH 15 IC can't start up. B
SWS 16 IC tries to start up. Possible power stage damage. B
XCD 17 XCD function is lost. Possible IC damage if VDD exceeds 30V. A
XCD 18 XCD function is lost. Possible IC damage if VDD exceeds 30V. A
VDD 19 No effect D
GTP1 20 IC is not biased. No PWML or PWMH output. Converter has no output. B
GTP2 21 IC is not biased. No PWML or PWMH output. Converter has no output. B
GTP3 22 IC is not biased. No PWML or PWMH output. Converter has no output. B
VS 23 OVP is triggered. IC shuts down and retries. Possible IC damage. A
SET 24 IC sets to Si MOSFET mode. Possible IC damage. A