LDO Regulator Application Note
Various protection circuits are built into Ricoh regulators.
The Auto-discharge Function
When you switch the regulator from the active mode to the standby mode with the CE pin, the VOUT pin voltage would not immediately fall to the ground level in case an output capacitor took time to discharge. To prevent this, Ricoh added N-channel transistor has been added the output circuit (shown in blue circles in the diagram below) in regulators having this function, so that any output capacitor can be promptly discharged.
This Auto-discharge function can be combined with the simplified system shutdown sequence.
- As shown in the figure on the left, the capacitor which is connected to the VOUT pin is discharged in 2.73s without the Auto-discharge function, whereas it is discharged in 126µs with the function.
- This Auto-discharge function ensures that output rapidly drops when the 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.
- Single LDO (Low Drop Out) regulator products include an Auto-Discharge function if the 10th character of product name is a "D".
(Example : R1114N281D-TR-F, RP103K281D-TR)
- Multi LDO (Low Drop Out) regulator products include an Auto-Discharge function if the 10th character of product name is a "B".
(Example : R5323N001B-TR-F, RP150K001B-TR)