RP173Q552B-TR-FE datasheet(9/22 Pages) RICOH

9 / 22 page

RP173x

REVERSE CURRENT PROTECTION CIRCUIT

The RP173 Series include a Reverse Current Protection Circuit, which stops the reverse current from VOUT pin

to VDD pin or to GND pin when VOUT becomes higher than VIN.

Usually, the LDO using Pch output transistor contains a parasitic diode between VDD pin and VOUT pin.

Therefore, if VOUT is higher than VIN, the parasitic diode becomes forward direction. As a result, the current flows

from VOUT pin to VDD pin.

The ICs of this series switches the mode to the reverse current protection mode before VIN becomes lower

than VOUT by connecting the parasitic diode of Pch output transistor to the backward direction, and connecting

the gate to VOUT pin. As a result, the Pch output transistor is turned off and the all the current pathways from VOUT

pin to GND pin are shut down to maintain the reverse current lower than [IREV] of the Electrical Characteristics.

Switching to either the normal mode or to the reverse current protection mode is determined by the magnitude

of VIN voltage and VOUT voltage. For the stable operation, offset and hysteresis are set as the threshold. The

detection/ release thresholds of both normal and reverse current protection modes are specified by [VREV_DET]

and [VREV_REL] of the Electrical Characteristics. Therefore, the minimum dropout voltage under the small load

current condition is restricted by the value of [VREV_REL].

Fig.1 and Fig.2 show the diagrams of each mode, and Fig.3 shows the load characteristics of each mode.

When giving the VOUT pin a constant-voltage and decreasing the VIN voltage, the dropout voltage will become

lower than the [VREV_DET]. As a result, the reverse current protection starts to function to stop the load current. By

increasing the dropout voltage higher than the [VREV_REL], the protection mode will be released to let the load

current to flow. If the dropout voltage to be used is lower than [VREV_REL], the detection and the release may be

repeated.

The operation coverage of the Reverse Current Protection Circuit is VOUT

≥ 1.5V. However, under the condition

of VIN=0V, always the reverse current protection mode is operating.

Fig. 1 Normal Mode

Fig. 2 Reverse Current Protection Mode

Fig. 3

Reverse Current Protection Mode Detection/ Release &

VREV_DET

VREV_REL

VOUT

VIN

Reverse Current Protection Mode

Normal Mode

IOUT

IREV

Reverse Current/ Output Current Characteristics

RP173Q552B-TR-FE Datasheet(PDF) 9 Page - RICOH electronics devices division