What is an auto-discharge function?

LDO Linear RegulatorsDC/DC Switching RegulatorsSwitch ICsFunction

When using a capacitor with large capacity value in VOUT side, the VOUT pin voltage might not immediately fall to the ground level when the EN(CE,CONTROL) pin is switched from the active mode to the standby mode.
By adding N-channel transistor to the output circuit (shown in blue circles in the diagram below), the auto-discharge function quickly lowers the VOUT to the ground level by releasing the electrical charge accumulated in the external capacitor. This auto-discharge function can be combined with the system shutdown sequence.

• During Operation

  

  When the CE pin is in the active mode, the LDO regulator is operating.
  The P-channel transistor circled in light blue is ON.
  The N-channel transistor circled in blue that provides the Auto-discharge function is OFF.

• During Standby

  

  When the CE pin is in the disable mode, the LDO regulator is in the standby mode.
  When in standby mode the P-channel transistor circled in light blue turns OFF and stops the LDO regulator output from the VOUT pin.
  The N-channel transistor circled in blue that provides the auto-discharge function turns ON and the charge in the output capacitor connected to the VOUT pin is rapidly discharged to the ground pin. It is called the "Auto-discharge function".

• 

  Without the Auto-discharge function

• 

  With the Auto-discharge function

• 

• As shown in the figure on the left, the capacitor which is connected to the VOUT pin is discharged in 2.73 s without the Auto-discharge function, whereas it is discharged in 126 µs with the function.
• This Auto-discharge function ensures that output rapidly drops when the LDO regulator enters standby mode, but it also effectively prevents system malfunctions that might occur by the capacitance of the output capacitor connected to the VOUT pin.