"RP108 Series" high current (3A) regulator with built-in reverse current prevention circuit to protect ICs from reverse current

RP108 Overview

The RP108 is a regulator (3A product) designed to cover the market trends of higher current, lower voltage, and lower noise, and is equipped with a "reverse current prevention function."

When the output voltage of an LDO is higher than the input voltage, it will affect the IC, and we are often asked the following question: "If the output voltage is higher than the input voltage, what effect will this have on the IC?"

If the output voltage in a circuit becomes higher than the input voltage, a large current will flow from the output to the input, which may destroy the IC.
This is because the transistor inside the IC has a parasitic diode (body diode), and when the voltage on the output side is high, the diode becomes forward, causing a reverse current to flow toward the input side.
However, if the current path on the input side is blocked when reverse voltage is applied, or if the reverse voltage source on the output side is not capable of passing a large current, there may be no problem.
For example, when the output of an LDO regulator is turned off, it is possible that current will temporarily flow back from the recommended capacitance to the input side, but this level of charge will not have any impact.

The built-in reverse current prevention circuit blocks the path that would otherwise reverse current, protecting the IC from damage even if the output voltage becomes high.
Even if a reverse current prevention circuit is not built in, it is possible to add an external diode to bypass the reverse current path to the external diode side.

There are three patterns for placing protective diodes in the peripheral circuits.

When connecting a diode to the output

The output voltage drops by the forward voltage (Vf) of the diode. However, in an LDO regulator where the output terminal (VOUT) and the feedback terminal (VFB, FB) are separate terminals,
As shown in the diagram below, this is a terminal for connecting a diode, and by connecting a diode, the output voltage can be controlled to a set voltage.

When inserting a diode into the input

The input voltage drops by the forward voltage (Vf) of the diode. This method is also effective if there is no problem with the input/output voltage difference.

When connecting a diode between the input and output

The reverse current can be bypassed by an external diode. Select one with a lower forward voltage (Vf) than the parasitic diode inside the IC.
Also, make sure that the reverse current does not exceed the current capacity of the diode.

In addition to a pattern that uses protective diodes, there is also a method of using a regulator with a built-in reverse current prevention circuit.

For details on the backflow prevention circuit, please click here.

Product Specifications

	Civilian	industry	In-vehicle
Input voltage range	1.6V ～ 5.25V(6.0V)
Operating temperature range	-40°C ～ 85°C(125°C)	-40°C ～ 105°C(125°C)	-40°C ～ 105°C(150°C)
Current consumption	Typ.350µA
Standby Current	Typ.2µA
Output Voltage Range	Internal fixed version: 0.8V ~ 4.2V (0.1V step) Externally adjusted version: 0.8V to 4.2V	Internal fixed version: 0.8V, 1.2V, 1.5V, 1.8V, 2.5V, 3.0V, 3.3V Externally adjusted version: 0.8V to 4.2V	Internal fixed version: 0.8V, 1.2V, 1.5V, 1.8V, 2.5V, 3.0V, 3.3V Externally adjusted version: 0.8V to 4.2V
Output Voltage Accuracy	±1.0%(Ta=25°C) (±15mV accuracy when VSET≤1.5V, Ta=25°C)
Output voltage temperature coefficient	Typ.±100ppm/°C
Input/Output Voltage Difference	Typ.0.51V (at VOUT=2.5V)
Input Stability	Typ.0.1%/V
Output Current	Min.3000mA
Ripple Rejection Rate	Typ.65dB (at f=1kHz, VOUT=2.5V)
package	TO-252-5-P2

Block Diagram

The IC is equipped with a circuit that prevents current from flowing from the VOUT terminal to the VDD terminal or GND terminal when VOUT is greater than VIN.
LDOs that use Pch output transistors typically have a parasitic diode between the VDD and VOUT terminals, so when VOUT is greater than VIN, the parasitic diode becomes forward, causing current to flow from the VOUT terminal to the VDD terminal.
The RP108J enters reverse current prevention mode before VIN becomes smaller than VOUT, and turns off the Pch output transistor by connecting the parasitic diode of the Pch output transistor in the reverse direction and connecting the gate to the VOUT terminal.
In addition, it blocks all current paths flowing from the VOUT terminal to the GND terminal, limiting reverse current to 10μA (Typ. 25℃).
Switching between normal mode and reverse current prevention mode is performed by judging the magnitude relationship between the VIN voltage and the VOUT voltage. To ensure stable operation, the judgment threshold has an offset and hysteresis. The RP108J has an offset of 30mV (Typ. 25°C) and a hysteresis of 5mV (Typ. 25°C), so the minimum input/output voltage difference that can be used in normal mode at light loads is restricted to 35mV (Typ. 25°C).

The diagram below shows an overview of the reverse current prevention circuit and the load characteristics for each mode.
When a constant voltage is applied to the VOUT pin and the VIN voltage is decreased, the reverse current prevention mode is activated when the input/output voltage difference falls below 30mV (Typ. 25°C) and load current cannot flow.
By raising the input/output voltage difference to 35mV (Typ. 25℃) or more, the device will return to normal mode and be able to draw load current.
When using the IC with an input/output voltage difference of less than 30mV (Typ. 25℃), detection and release may occur repeatedly.