Where is it used?

Battery management ICs are used in a wide range of battery-powered applications, including smartphones, laptops, power tools, vacuum cleaners, electric bicycles, energy storage systems (ESS), and uninterruptible power supplies (UPS). The number of series cells (and thus voltage) in a battery varies greatly depending on the application, covering a wide range from 1 cell to over 20 cells.

Low voltage (1 Cells: Smartphones, hearing aids, TWS earphones, etc.
Medium voltage (4 Cell before and after): Note PC /tablet, POS Terminals, medical devices, AED etc.
• High voltage (10 Cell front and back): Power tools, vacuum cleaners, electric assist bicycles, energy storage systems, UPS etc.
・Large power (20 Cell (Super): AGV / Forklifts, etc.

These battery management ICs are primarily integrated into battery pack systems.

Figure 1: Examples of battery-powered devices by voltage and capacity.

Source: Renesas Electronics Corporation, "PB078_ROB-K-25-0089_FGIC_Basic.PDF", p. 9

Types of battery management ICs

Battery pack systems can be broadly divided into three types.

1. Protection IConly: Basic functions (FET off, fuse blow protection only). Suitable for low-power, simple applications (toys, mobile phones, portable devices, etc.). Not suitable for advanced battery management.
2. AFE+ MCU(2-chip configuration): A multi-functional, highly expandable configuration combining an AFE (analog front-end) and an MCU. Suitable for multi-cell, high-power applications (automotive, industrial, power tools, electric bicycles, etc.). However, challenges include increased BOM / PCB area and increased complexity of BMS design.
3. Integrating AFE+ MCU into ​a singlepackage (= FGIC): Achieves multi-functionality while reducing BOM and PCB space. By selecting the optimal product for each application, the limitations of scalability due to integration are compensated for.

*AFE (Analog Front End) refers to the circuit block responsible for the initial processing that converts analog signals into digital signals.

This article introduces Renesas' FGIC teeth, 3 The second"AFE+ MCUof 1"Integrated into the package" type This applies to this category.

Figure 2: Comparison of Battery Pack System Configurations

Source: Renesas Electronics Corporation, "PB078_ROB-K-25-0089_FGIC_Basic.PDF", p. 13

Reason ①: To ensure the "safety" of lithium-ion batteries.

Lithium-ion batteries are more powerful than other types of batteries, If used incorrectly, it may cause overheating, fire, or explosion in the worst-case scenario. There have been reports of fires caused by non-genuine batteries, so extreme caution is necessary when handling them.
Battery Management I C This system provides multi-layered protection against these risks, from both hardware and software perspectives. Specifically, it offers the following features:
 
- Physical protection by fuses (permanent fault control)
FET Charge/discharge control and protection
- Overvoltage/undervoltage detection, cell imbalance detection, full charge/full discharge detection
• Temperature monitoring
- Overcurrent protection/short circuit detection, capacity calculation, degradation detection
 
By combining these, protection I C It maintains a higher level of safety. Safely managing batteries protects user safety and enhances product reliability. This is directly related to that.

Figure 3: Example of a fire accident caused by a lithium-ion battery.

Source: Japan Hazardous Materials Safety Association

(URL) Beware of lithium-ion battery fires

Reason ②: To "accurately" detect the remaining battery level.

Lithium-ion batteries do not experience a constant voltage drop as they discharge (the voltage-capacity characteristic is non-linear). Therefore, it is difficult to accurately determine the remaining charge (SOC: State of Charge) by looking at the voltage alone.

The battery management IC combines real-time voltage monitoring with current integration (Coulomb counting), cell balancing, and temperature-based degradation correction to calculate the accurate remaining battery level, which cannot be determined by voltage alone. This prevents problems such as "the battery level display does not reflect the actual level."

Figure 4: Image of battery level estimation with and without 　FGIC​

Source: Created by Macnica (Based on page 6 of Renesas Electronics Corporation's "PB078_ROB-K-25-0089_FGIC_Basic.PDF")

The diagram above shows the discharge characteristics (relationship between voltage and capacity) of a lithium-ion battery. Lithium-ion batteries have the characteristic that the voltage does not decrease linearly as the remaining charge decreases, but rather maintains a constant voltage range for a long period before dropping sharply.

The red line (without FGIC) represents the case where the remaining charge is estimated solely from voltage. This underestimates the remaining charge at 4Ah discharge, judging it to be approximately 3.0V. On the other hand, the blue line (with FGIC) calculates the remaining charge using not only voltage but also current integration (Coulomb counting) and degradation correction, allowing it to accurately perceive approximately 3.3V at the same 4Ah discharge, which is closer to the actual battery state.

By using FGIC in this way, battery level can be estimated with high accuracy even in areas where it is difficult to judge based on voltage alone, leading to a reduction in errors in the remaining charge display and maximization of usable capacity.

*The diagram is a schematic representation of the remaining charge estimation method. The presence or absence of FGIC does not change the battery's discharge characteristics themselves.

Reason 3: Benefits of accurate remaining battery level detection

High-precision detection of remaining battery charge can increase the actual"usable capacity"of the battery. If the ADC 's measurement accuracy is low, an extra safety margin must be maintained at both the fully charged and completely discharged ends, which reduces the actual usable capacity. Conversely, using a high-precision ADC reduces this margin, leading to an increase in usable capacity and, consequently,an extension of the product's operating time.

Figure 5: Comparison of usable capacity based on 　ADC measurement accuracy.

Source: Renesas Electronics Corporation, "PB078_ROB-K-25-0089_FGIC_Basic.PDF", p. 6

Feature ①: High security through hardware + software

FGIC implements both Safety control and Remaining Capacity management from both hardware and software perspectives.

Table 1: Safety control and remaining capacity management functions of FGIC

Figure 6. Main functions of safety control and remaining fuel management by FGIC. 

Source: Renesas Electronics Corporation, "PB078_ROB-K-25-0089_FGIC_Basic.PDF", p. 4 

Feature ②: High-precision remaining quantity detection using an industry-leading 18-bit ΔΣ ADC.

The reason FGIC can accurately detect remaining battery life lies in Renesas' proprietary ΔΣ(delta-sigma) ADC. Renesas' FGIC incorporates an 18-bit ΔΣ ADC for current and a 15-bit ΔΣ ADC for voltage and temperature.

Conventional SAR ADCs sample instantaneous values, which means they miss current changes between samples, leading to reduced capacitance accuracy. On the other hand, ΔΣ ADCs output average values (integral values), allowing them to accurately trace charge and discharge currents and perform high-precision current integration over a wide range. Furthermore, they have the advantage of eliminating the need for offset measurement thanks to the use of a dedicated ADC reference with no temperature drift. This increased precision expands the aforementioned"usable capacity,"leading to extended operating time of the equipment.

FGIC Internal Configuration

The FGIC integrates an AFE block (series regulator, Nch FET control, battery voltage detection circuit, 15-bit ΔΣ ADC, overcurrent detection circuit, 18-bit ΔΣ ADC = Coulomb counter, etc.) and an RL78 CPU + Flash / RAM + various communication interfaces (I2C / SMBus, UART, SPI, CAN, etc.) into a single package. This simultaneously reduces the number of external components, miniaturizes the device, and achieves ultra-low power consumption.

Main specifications of representative products

RAJ240055/ 057(2~ 4For cells):64KB / 128KB Code Flash, SMBus3.0 Support, high side FET control, 15 bit ΔΣ ADC (Voltage, current, temperature) 18 bit ΔΣ ADC (Coulomb counter), overcurrent detection, 3ch Thermistor compatible, cell balance circuit (Typical 100Ω), minimum operating voltage 2.2V, operating temperature-40 ~ 85℃, 32 pin QFN (4 x 4 mm). Notebook PC, TWS For use in handheld medical devices, drones, power tools, etc.

RAJ240090/ 100(for 3-8​/​3-10​cells):128KB Code Flash, 7KB RAM, CAN compatible, high-side FET control, 15-bit/ 18-bit ΔΣ ADC, overcurrent detection, cell balancing circuit (Typ. 200Ω​), operating voltage 4.0-50V​, operating temperature-40-85​ ​℃, 64-pin LQFP (10×10mm). For use in power tools, vacuum cleaners, electric bicycles, energy storage systems, UPS, etc.

FGIC Starter Kit

An evaluation board with a reference design and sample code is included, allowing for a simple initial evaluation.
- Allows evaluation of device functionality and performance.
RL78 For development E2 Supports emulator connection
- Provides sample code that implements basic battery management functions.
・ Via communication board PC Connect it and monitor the battery status such as voltage, current, and temperature. GUI Monitorable

Starter Kit R-BMS F (Firmware Development-Free Solution)

R-BMS F This is Renesas' FGIC For Equipped with pre-designed firmware BMSTotal Solution Therefore, firmware development is not required. BMS This significantly simplifies development and shortens the time to market. TTM) can be shortened.

Three values

• Easy-to-Use: Even without programming knowledge, it can be used with intuitive operation via a dedicated GUI.
• Quick Design:​ ​The firmware is pre-programmed during the PCB manufacturing process. Compatibility with various lithium batteries is achieved simply by changing parameters.
• Safe System: Equipped with basic battery protection functions and features designed for mass production.

Benefit ①: Significant reduction in development time

Traditionally, the development process involved a long sequence of steps: hardware design → firmware design → firmware debugging → evaluation → system testing → product launch. With R-BMS F, the pre-installed firmware eliminates the need for firmware design and debugging, significantly shortening the development period.

Figure 7:Example of shortened development time usingR-BMS F Tool

Source: Renesas Electronics Corporation, "PB078_ROB-K-25-0089_FGIC_Basic.PDF", p. 21

Benefit ②: Start evaluation with simple initial setup.

You can start the evaluation by simply performing a few initial settings, such as the number of cells used, nominal capacity, and voltage/current thresholds (using the GUI tool "R-BMS F Tool").

Offerings

Hardware: Evaluation board (EVM), USB SMBus I/F, cables
Firmware: Voltage, current, and temperature measurement; FCC / RC / RSOC calculation; safety functions (overvoltage/undervoltage, overcurrent/short circuit current, overheating/low temperature); high-side Nch FET control; cell balancing.
• Software: Dedicated GUI tool "R-BMS F Tool" for monitoring, control, and parameter modification.
• Documentation: Manuals, evaluation board (EVM) circuit diagrams

*The ICs on the EVM are shipped with firmware and parameters pre-programmed (unprogrammed when purchasing the IC separately). FCC: Full Charge Capacity / RC: Remaining Capacity / RSOC: Relative State Of Charge.

Figure 8.Example configuration ofthe R-BMS F evaluation kit.

Source: Renesas Electronics Corporation, "PB078_ROB-K-25-0089_FGIC_Basic.PDF", p. 22

Table 3: List of R-BMS F compatible models