Let’s take mobile device charging as an example. How do we design a reverse current protection scheme? If you are unfamiliar with reverse current protection, please refer to “What is Reverse Current?”.
Modern mobile devices have many power supply methods, such as the common TYPE-C DC 5V, internal battery power 4.2V, or power adapter power.
We previously analyzed the case where these three power supplies are connected individually. When these three power supplies are connected simultaneously, how can reverse current protection be achieved? In this circuit design, the power adapter has the highest priority, followed by the TYPE-C input, with the battery input supplying the load. Why is it designed this way? Let’s analyze it:
Circuit Principle:
Power adapter connects to reverse current protection D1, which outputs to the load stage circuit. At this point, the voltage at point A is 4.7V. Through resistor R2, the Vgs voltage of Q1 is pulled high. The reverse current protection PMOS (AO3401A) is cut off, disconnecting the TYPE-C output. The input voltage of the power adapter cannot flow into TYPE-C. Because the output power adapter provides a 4.7V output voltage, the voltage at point C is also 4.7V. Since the RCE pin of the LM66100DCK is connected to the VOUT pin at point C, the voltage at point C is higher than the battery voltage. Therefore, the internal PMOS of the LM66100DCK is cut off and no output is generated. Currently, the power adapter is supplying power to the downstream load.
When TYPE-C and the battery are connected, the **potential at point A is 0V, which pulls down the Vgs voltage of Q1 through resistor R2. The reverse current protection PMOS AO3401A turns on, and TYPE-C outputs 5V. Because TYPE-C outputs 5V, the CDC and CE pins are connected to VOUT point C through **resistor R4. When CE is 5V, the internal PMOS is cut off and does not output. Therefore, TYPE-C supplies power to the downstream load at this time.
Reverse current protection methods vary. Based on circuit current, efficiency, and cost, we’ll share three reverse current protection solutions:
- Reverse Current Protection - Diode
- Reverse Current Protection - MOSFET
- Reverse Current Protection - Ideal Diode
- Reverse Current Protection - Simultaneous Use of Diode + MOSFET + Ideal Diode
Related Parts: