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RP173K251B-TR Datasheet(PDF) 9 Page - RICOH electronics devices division |
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RP173K251B-TR Datasheet(HTML) 9 Page - RICOH electronics devices division |
9 / 22 page RP173x 9 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 0 Reverse Current Protection Mode Normal Mode Normal Mode IOUT IREV Reverse Current/ Output Current Characteristics |
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