SCEA144 December   2024 LSF0101 , LSF0102 , LSF0108 , LSF0204

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1How Does the LSF000x Differentiate From the LSF010x During Setup?
  5. 2How is the Internal Body Diode of the LSF NMOS Configured?
  6. 3Are Pullup Resistors Required for Push-Pull Applications with the LSF?
  7. 4How is Power Consumption Calculated for LSF Devices?
  8. 5Can I use LDO as a Power Supply?
  9. 6What if my I/Os Operate Lower Than VREFA?
  10. 7Summary
  11. 8References

5 Can I use LDO as a Power Supply?

During normal operation, there exists a leakage current that flows into the high-power supply (typ. referenced as VREFB) and out the lower power supply (typ. referenced as VREFA). The current flowing through the device is limited by the 200kΩ bias resistor to limit the current flowing through the internal FET and protect the lower supply from being overexposed to the otherwise high current, which can be presented by VREFB-VREFA-VTH/200k.

Using LDO Power Supply with LSF Figure 5-1 Using LDO Power Supply with LSF

Not all power supplies are capable of sinking in this back current, which is especially for the case when using low dropout regulator (LDO) as a power supply. If the LDO cannot sink this current, the LDO causes the power supply to float up above the expected levels of where it was at previously. For cases where the I/Os are also pulled up to LDO, their voltage levels also rise and can potentially damage both the signaling devices and the power supply. To accommodate for this current that cannot be accepted by the lower power supply, we recommend to add a relatively weak pulldown resistor at this node to create a path for the current to sink into instead.