In everyday life, devices like smartphones, laptops, and other consumer electronics typically contain circuit systems with control ICs, power MOSFETs, and other electronic components, which can be referred to as Protection Circuit Modules (PCM).

Today, we will discuss the working principle analysis of VBsemi power MOSFETs in PCM protection circuit modules.

PCM generally requires power MOSFETs with low on-state resistance, so engineers often choose N-channel power MOSFETs. However, in some applications, P-channel MOSFETs are used at the positive terminal for flexible driving. But compared to NMOS, the on-state resistance of PMOS is relatively higher than NMOS, which may be limited in many selections.

Working Principle of VBsemi Power MOSFET in PCM

PCM uses one power MOSFET for charging and another for discharging. The two N-channel power MOSFETs used for managing charging and discharging are placed at the ground end, with their drains back-to-back connected.

There are two configurations for connecting back-to-back in parallel: one configuration connects the drains of the two power MOSFETs, and the other connects their sources.

From the figure, we can see two power MOSFETs, Q1 and Q2: Q1 is used for battery discharge, and Q2 is used for battery charging. Before the PCM board works, both Q1 and Q2 are in the off state.

B+/- is the positive and negative terminals of the battery; P+/- is the positive and negative terminals of the battery pack; VSS is the ground of the battery protection management IC, i.e., the negative terminal of the battery; VSS is connected to the power supply of Q1.

Regarding the "charge and discharge" operation of MOSFETs in it

Charging

During charging, when the control IC gate is controlled, it provides a drive signal CO to the power MOSFET Q2, the path is: the positive terminal of the external charging circuit → P+ → B+ → R1 → VDD → CO → Q2 source → P- → the negative terminal of the external charging circuit.

When Q2 is turned on, the charging path is: P+ → B+ → B- → the internal parasitic diode of Q1 → Q2 channel → P-

Then the battery can be charged.

To reduce the loss of Q1, when Q2 is turned on, the DO pin of the control IC can be pulled high to turn on the discharge Q1 power MOSFET.

Discharging

During discharging, when the control IC provides a gate drive signal DO to the discharge Q1 power MOSFET, the gate drive signal path of Q1 is: VDD → DO (driver output → Q1 gate → Q1 source → B- → VSS.

Then, when Q1 is on, the discharge current path is: P → the internal parasitic diode of Q2 → Q1 channel → B- → B+ → P+, and the battery starts to discharge.

To reduce the loss of Q2, when Q1 is turned on, the control IC will provide a gate drive signal CO to the charging power MOSFET Q2, and then turn on Q2. At this time, Q1 and Q2 are both in the on state.

Performance Requirements

In order to achieve higher charging efficiency and reduce charging time, rapid charging techniques with increased current are usually adopted. This poses more stringent technical challenges for power MOSFETs in high-current charging applications. Therefore, when selecting power MOSFETs, lower on-state resistance, smaller size, higher power density, and better heat dissipation capability are required.

To ensure reliable performance and improve operational stability in applications such as battery charge and discharge management, protection and control, signal amplification, and switch control, VBSEMI's power MOSFET products can be used.

The choice of various packaging designs provides high flexibility and integration for various circuit applications, with advantages such as low on-state resistance, low power consumption, high-speed switching, and improved heat dissipation performance.