SDAA137 June   2026 UCD91160 , UCD91320

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Frequently Asked Questions
    1. 2.1 Sequencer Studio GUI FAQs
      1. 2.1.1 Can the Sequencer Studio generate a data flash image file (.hex) while working without a device connected?
      2. 2.1.2 How Do I Configure Margining in Sequencer Studio?
      3. 2.1.3 How Do I use Voltage Trimming?
      4. 2.1.4 How Do I Set ADC Voltage Divider Settings?
      5. 2.1.5 How Do I Configure the Black Box Fault Log?
      6. 2.1.6 How Can I Read the Device Firmware Image?
    2. 2.2 Hardware FAQs
      1. 2.2.1  Are Pulldown Resistors Required on EN Pins?
      2. 2.2.2  Are the Decoupling Capacitors Required on MON Pins?
      3. 2.2.3  What is The Value of the Tank Capacitor?
      4. 2.2.4  Can Less than Three GPIs Be Used for PIN SELECTED RAIL STATE (PSRS)?
      5. 2.2.5  Can the Logical General Purpose Output (LGPO) Be Used as an Enable?
      6. 2.2.6  How Should Users Implement a Power-Down Sequence When the Rails ON_OFF_CONFIG are Set to Always On?
      7. 2.2.7  Can the RESET Pin be Used to Sequence Off Rails?
      8. 2.2.8  Is an RC Filter Needed for External VREF?
      9. 2.2.9  What is the CONTROL Pin Used For?
      10. 2.2.10 What Are the States of IO Pins When The Pin is Under Reset?
      11. 2.2.11 Are These Devices Tested for Radiation?
      12. 2.2.12 What Are the Options to Configure Devices?
    3. 2.3 Software FAQs
      1. 2.3.1  How Can Users Re-sequence All Rails After They are Off due to Fault Response When the Rails are ON_OFF_CONFIG are set to AUTO Mode?
      2. 2.3.2  How do Users Know that the Sequencing Dependencies are Met?
      3. 2.3.3  Is Clock Stretching Required by the PMBus Master?
      4. 2.3.4  What are Restart (Retry) and Re-sequence?
      5. 2.3.5  What are the Fault Shutdown Slaves?
      6. 2.3.6  What Happens when the Fault Log is Full?
      7. 2.3.7  How Can Users Re-sequence All Rail After They are off due to Fault Response When the Rails are ON_OFF_CONFIG are Set to AUTO Mode?
      8. 2.3.8  When Importing a Project File into a Device, Why Do Some GPIO Pins Unexpectedly Turn On and Off?
      9. 2.3.9  When is the Re-sequencing Count Reset?
      10. 2.3.10 When is the Retry Count Reset?
      11. 2.3.11 Why are the Fault Shutdown Slave Rails Not Off Immediately?
      12. 2.3.12 Why Are The Rails Off Immediately Instead of Following the Sequencing Settings (Dependencies, TOFF Delay) when Toggling the CONTROL?
      13. 2.3.13 Why are the settings not saved after device reset?
      14. 2.3.14 Why Are There No Undervoltage Faults? For Some Reason, the Rails Do Not Start
      15. 2.3.15 Why Do Rails not Re-sequence After Restart is Exhausted?
      16. 2.3.16 Why Do the Rails Not Start or Stop?
      17. 2.3.17 Why Does the Time Interval Between Two Re-sequences Longer than the Value Set in Time Between Re-sequences?
      18. 2.3.18 Why Does the Turn-on and Turn-off Sequence or Re-sequence Hang, or Take Very Long to Complete?
      19. 2.3.19 Why is a Fault Logged even if the Fault is Ignored by a Glitch Filter?
      20. 2.3.20 When is POWER_GOOD Fault Flag Set?
      21. 2.3.21 What is the Difference Between Resequencing and Retries?
      22. 2.3.22 How Quickly Can UCD Detect and Respond to a Fault?
      23. 2.3.23 Why Does the GPI Not Turn Off the Rails when it is De-asserted if the GPI is Configured as a Rail Sequence-Off Dependency?
    4. 2.4 PMBus FAQs
      1. 2.4.1 Is Packet Error Code Required by the PMBus Master?
      2. 2.4.2 Is the PMBus Connector for the Sequencer Studio GUI Still Required if a PMBus Host is Already Available?
      3. 2.4.3 What is an ALERT Signal?
      4. 2.4.4 Can The GPI Status of a UCD91xxx Be Read Over The PMBus?
    5. 2.5 Margining FAQs
      1. 2.5.1 Are There any Application Notes for Margining Function?
      2. 2.5.2 Does the UCD91xxx Family Support Voltage Margining?
      3. 2.5.3 When does the UCD91xxx start rail margining?
  6. 3Summary
  7. 4References

2.2.3 What is The Value of the Tank Capacitor?

The size of the tank capacitor is largely dependent on how long you want the device to continue running after a power loss. If functional black box fault logging is desired, the tank capacitor must be large enough to keep the supply voltage above 1.62V for at least 825us to allow the last black box fault log to finish writing off.