DCDC/LDO Auto-Discharge

1、概念

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.

Normal Operation	Standby
CE = 1： 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.	CE = 0： 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.

TI TPS62873和Silergy SY8893支持auto-discharge功能。

2、效果

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.

Without the Auto-discharge function	With the Auto-discharge function

 

3、应用场景

• FT/SLT等场景下，需要频繁上下电，更换芯片的，如果电源没有auto-discharge，则下电很慢，可能导致芯片带电更换，存在风险。