Table of Contents
How Battery Protection PCB / Protection Circuit Module (PCM) Keep Lithium-ion Battery Safe?
We’ve already learned the basics about battery PCBs, charging PCBs, protection PCBs, and BMS. This blog post will focus on battery protection PCBs, explaining how protection circuit modules ensure the safety of lithium batteries.
Lithium batteries provide the power source for most of the portable devices we use today. The high energy density of these batteries makes them the best energy source for most applications. However, lithium batteries are sensitive to certain parameters. If the battery is overcharged, overdischarged, or if the battery is overheated or even too cold, the battery can be degraded or damaged in the worst-case scenario.
This is why a Battery safety circuit is required. The most common form of such a circuit is the Protection Circuit Module (PCM). A PCM is a control board that continuously monitors the batteries and ensures that the battery is not exposed to any conditions that would damage it or affect its health. Essentially, it is the last line of defense for the battery. In this article, we will discuss how it works, its components, the different types available, considerations for designing these circuits, and common mistakes when integrating a PCM into a Battery protection PCB.
What Is a Lithium Battery Protection Board (PCM)?
A lithium battery protection PCB (printed circuit board) is a control board that is physically positioned between the cells of the battery and the main application board. Actually, it’s a protection circuit module (PCM), which acts as a safety protection device for rechargeable lithium-ion (Li-ion) or lithium polymer (LiPo) batteries by protecting the individual battery cells from the causes that can harm them.
Lithium-ion battery protection is critical because these batteries are chemically unstable, unlike older types (e.g., nickel-metal hydride or lead-acid). They can overheat, burn, or even explode if they are overcharged, over-discharged, or short-circuited. The PCM tracks the voltage, current, and temperature inside the battery and manages the battery connection to the rest of the circuit to avoid these dangerous situations.
How Does a Battery Protection Board Work?
Overvoltage protection (OVP)
If the cell voltage exceeds the maximum threshold voltage, the PCM shall disconnect the charge MOSFET to disconnect the charging source from the battery cell. Overcharging leads to a reduction in the battery capacity, which reduces the state of health SOH.
Undervoltage protection (UVP)
When the voltage of the cell drops to a minimum threshold voltage, the PCM shall turn off the discharge MOSFET. Discharging a battery to very low voltages will damage the cell and permanently reduce the battery’s capacity to store charge, which also reduces the state of health SOH.
Overcurrent/short circuit protection (OCP)
In the case of a short circuit in the battery or its load, the PCM circuit shall detect the high discharge current and quickly turn off the discharge MOSFET within microseconds to avoid damaging the battery and the load.
Temperature protection (for advanced batteries)
More advanced batteries have integrated NTC thermistors that measure the temperature of the battery cell. If the battery is overheated, the PCM shall turn off both load’s charge and discharge MOSFETs to stop the charging or discharging of the battery until the temperature returns to a safe range.
Key Components of a Protection Circuit Module (PCM)
Understanding the internal components of a PCM circuit allows for the evaluation of the quality of that PCM and whether or not it may be suitable for a given application.
Protection IC:
The protection IC is the “brain” of the PCM and is responsible for monitoring the voltage and current of the cell. For single cells, the most common ICs include DW01A, S-8261, and the BQ29700. For multi-cell batteries, the BQ29330 can manage up to 3 cells in series, the ISL9208 from Renesas, and the ISL9208 also allows for communication between the PCM circuit and another system.
MOSFETs (charge and discharge FETs)
There are at least two MOSFETs in any PCM, one controls the charging of the cell, and the other controls the discharging of the cell. The FS8205A is one of the most common MOSFETs to be utilized in conjunction with a single-cell protection IC, such as the DW01A.
Current Sense Resistor:
A current sense resistor allows the protection IC to measure the current of the battery. A small resistor is placed in series with the battery, then amplified. Current sense resistors should be in the mΩ range, depending upon the current that is to flow through the battery.
Types of Lithium Battery Protection PCBs
The complexity of the protection circuit differs based on the type of lithium batteries that are being used.
- Single-Cell PCM: As the name suggests, these protection circuits are used for batteries that contain a single cell within them. They provide protection for the battery from various issues that can occur and are used in devices such as earbuds or wearables.
- Multi-Cell PCM: These protection circuits are used for batteries that contain more than one cell. In addition to providing the typical protections for the batteries, these circuits include charge-balancing circuitry so that the charge within each cell is balanced with the others, so that no cell is discharged at a faster rate than the others.
- PCM with Fuel Gauge: These protection circuits also include a fuel gauge circuit so that it is possible to measure the level of charge that is within the battery. These are used in devices like laptops or power banks.
PCM vs. BMS: What's the Difference?
Many engineers confuse a Protection Circuit Module (PCM) with a Battery Management System (BMS). While both monitor batteries, they serve different roles:
| Feature | PCM | BMS |
| Primary function | Emergency protection (cutoff) | Monitoring, balancing, control |
| Cell balancing | No (except very basic multi-cell PCMs) | Yes (active or passive balancing) |
| Communication | None (just on/off) | Often I²C, SMBus, CAN bus |
| Typical use | Single-cell (1S) or simple 2S packs | E-bikes, EVs, solar storage (≥3S) |
| Cost | Low ($0.50–$3) | Higher ($5–$50+) |
Why this matters: If your application requires cell balancing or state-of-charge (SoC) reporting, a standalone PCM is insufficient. You need a BMS. Conversely, for a simple 18650 battery pack in a flashlight, a PCM is perfect and cheaper.
Battery PCB vs Charging PCB vs Protection PCB vs BMS
Confused about Battery PCB vs Charging PCB vs Protection PCB vs BMS? This guide explains functions, components, and applications. Includes difference between battery protection board and BMS, selection tips, and FAQ.
Design Guidelines for Battery Protection PCB
PCM circuit can be ready-made modules or can be integrated into designs as a part of it. Now we will talk about integrating it into our design and list the layout guidelines to achieve the required performance.
- Trace width is the most important consideration in all power electronics projects’ layout. The most important traces are charging & discharging paths; they should handle high current without excessive heating. The rule of thumb is “As Wide As Possible, As Short As Possible”. Look at the provided IPC recommended PCB trace width calculator; it’s not 100% accurate because there are many parameters, but it’s still a great point to start.
- Gate Signal Routing is also a critical point when routing PCMs, as charge and discharge MOSFETs should be short and direct. This high-frequency signal should be immune to noise, which can cause false triggering or slow switching response. Also, the gating resistor should be small (typically 10–100 Ω) and placed near the MOSFET gate terminal to provide a discharging path for MOSFET gate-source capacitance.
- The protection IC’s power supply decoupling should be clean. Noise on the supply may cause an unintended function of the integrated circuit, resulting in false triggering of charging and discharging MOSFETs. Placing a low resistance decoupling capacitor near the Vcc pin will act as an energy reservoir and filter the supply noise.
5 Common Mistakes When Integrating a PCM into a PCB
❌ Mistake #1: Routing charge/discharge traces too thin
❓️Result: Voltage drop and overheating.
✅ Fix: Use copper pours or multiple parallel vias. For 10A, use at least 3mm trace width (1 oz copper).
❓️Result: Voltage drop and overheating.
✅ Fix: Use copper pours or multiple parallel vias. For 10A, use at least 3mm trace width (1 oz copper).
❌ Mistake #2: Placing the current sense resistor too far from the protection IC
❓️Result: Noise and inaccurate overcurrent detection.
✅ Fix: Place the sense resistor within 5mm of the IC’s CSP (current sense positive) and CSN pins. Use Kelvin connections.
❓️Result: Noise and inaccurate overcurrent detection.
✅ Fix: Place the sense resistor within 5mm of the IC’s CSP (current sense positive) and CSN pins. Use Kelvin connections.
❌ Mistake #3: Ignoring the PCM’s quiescent current (Iq)
❓️Result: Battery drains faster than expected during storage.
✅ Fix: For low-power IoT devices, select a PCM with a quiescent current of less than 3µA (e.g. Seiko S-82 series).
❓️Result: Battery drains faster than expected during storage.
✅ Fix: For low-power IoT devices, select a PCM with a quiescent current of less than 3µA (e.g. Seiko S-82 series).
❌ Mistake #4: Using a single PCM for parallel cells without cell matching
❓️Result: One weak cell can trigger protection while others are fine.
✅ Fix: If you have parallel cells, pick cells with the same voltage, capacity, and internal resistance. Or install a separate PCM for each cell string.
❓️Result: One weak cell can trigger protection while others are fine.
✅ Fix: If you have parallel cells, pick cells with the same voltage, capacity, and internal resistance. Or install a separate PCM for each cell string.
❌ Mistake #5: Not adding a reverse polarity protection for the charger input
❓️Result: If the user reverses charger leads, the charge MOSFET body diode can conduct, leading to IC destruction.
✅ Fix: Insert a Schottky diode or a second back-to-back MOSFET at the charger input.
❓️Result: If the user reverses charger leads, the charge MOSFET body diode can conduct, leading to IC destruction.
✅ Fix: Insert a Schottky diode or a second back-to-back MOSFET at the charger input.
Conclusion
Lithium battery PCMs are a critical component of any product powered by batteries. The PCM plays a crucial role in ensuring the safety of the cell, extending the battery life, and protecting the users and their equipment from damage caused by battery failure modes. Whether you call it a Battery protection PCB, a Battery safety circuit, or a Protection circuit module (PCM), the goal remains the same: reliable Lithium-ion battery protection.
Today, in this article, we have covered the working of PCMs, the components of a protection circuit, the different types of PCMs available, and how to choose the right protection circuit for your battery. Regardless of your product idea, the protection circuit is just as crucial as the battery cell for your product.
Visit FS Tech or contact us today to order your battery PCM circuit with our engineering team.
Final checklist before ordering your PCM: Confirm cell chemistry, continuous current, OCP threshold, and operating temperature range. When in doubt, request engineering samples from your supplier (like FS Tech) and test them under your actual load conditions.
FAQs
A PCM is made for protection from overvoltage, undervoltage, and overcurrent. A BMS is made for charging, balancing, monitoring, and communicating with external systems.
The battery may be affected by unsensed overvoltage, undervoltage, or any harmful condition. This reduces battery life span and effective capacity over time.
Overcurrent protection takes tens of milliseconds to react with currents above the design or rated current. Short-circuit protection responds within microseconds to a sudden hard fault.
The MOSFET, in line with the fault location (charge or discharge), will be turned off to isolate the battery from the circuit until the fault condition is resolved.
Yes. Custom threshold voltages, current limits, and communication features can be specified. Working closely with the PCM supplier or designing a custom protection circuit gives engineers control over all parameters.
No. PCMs are calibrated for lithium chemistries. NiMH requires a different voltage detection circuit (e.g., -ΔV for charge termination). Using a Li-ion PCM on NiMH will either not protect properly or cause false trips.
Related Blogs
13 October, 2026
Drone PCB Design and Manufacturing: A Complete Guide for UAV Engineers Read More »
Table of Contents Drone PCB Design and Manufacturing: A Complete Guide for UAV Engineers This article was originally published in March 2024 and last updated
9 October, 2026
Security Camera PCBA Design Guide: Day/Night Switching and Infrared LED Driver Read More »
Table of Contents Security Camera PCBA Design Guide: Day/Night Switching and Infrared LED Driver Why Security Camera PCBA Design Matters for Day/Night Operation A security
6 October, 2026
AgTech Case Study: Manufacturing 2,000+ Agricultural Sensor Devices from Prototype to Production Read More »
Table of Contents AgTech Case Study: Manufacturing 2,000+ Agricultural Sensor Devices from Prototype to Production Designing an electronic prototype to large-scale production requires more than
3 October, 2026
Agricultural Drone PCBA Assembly: High-Current, Lightweight & Durable Design for Farm UAVs Read More »
Table of Contents Agricultural Drone PCBA Assembly: High-Power, High-Current Solutions for Farm UAVs [2026] There is growing demand for modern agricultural drones as a means
26 September, 2026
2026 China PCB Manufacturer List: Top 10 PCB Suppliers in China Read More »
Table of Contents 2026 China PCB Manufacturer List: Top 10 PCB Suppliers & PCBA Companies in China This article was originally published in July 2022
22 September, 2026
We'd love to hear from you