What is the Analog Front End (AFE)?

The battery management system (BMS) is the "brain" of the lithium-ion battery pack, which conducts unified monitoring, command and coordination of the battery cells (group). In terms of composition, the battery management system includes a battery management chip (BMIC), an analog front end (AFE), an embedded microprocessor, and embedded software. Based on the battery state data collected in real time, the BMS realizes the voltage protection, temperature protection, short circuit protection, overcurrent protection, insulation protection and other functions of the battery pack through specific algorithms, and realizes the voltage balance management and external data communication between the batteries.

In this blog, we will learn about the analog front end (AFE) in BMS, and deepen everyone's understanding of BMS by analyzing the role of analog front end, chip selection, common products on the market, and the choice of MAXKGO.

l What is an Analog Front End

When detecting the state (voltage and temperature) of battery cells, we need to use BMS AFE (battery management system analog front-end chip). AFE is a monitoring chip with multiple sampling channels, which can monitor the cell voltage and Temperature monitoring. Analog front-end chips generally include 16-bit ADCs, high-precision voltage references, high-voltage multiplexers, and an SPI interface, and are typically used in electric vehicles, high-voltage mobile devices, backup battery systems, and high-voltage data acquisition systems.

l Analog Front End (AFE) Industry Analysis

The analog front end (AFE) is the basic system building block of sensor circuitry, used to amplify and/or filter sensor signals that are often weak and may have complex electrical configurations to support different MCUs. Its purpose is to process the analog signal given by the signal source, digitize and analyze it.

The main functions of AFE include signal amplification, filtering, receiving ADC, frequency conversion, adjacent frequency processing, level adjustment and control, etc. AFE is widely used in communication, automobile, medical, smart instrument, consumer electronics and other fields. In recent years, with the upgrading of downstream industries, the AFE market is gradually upgrading towards miniaturization, high integration and multi-channel.

Globally, core analog front-end (AFE) manufacturers mainly include Analog Devices, Inc. (ADI), Texas Instruments, Microchip Technology, ST Microelectronics, Cirrus Logic, and NXP. In 2021, the world's first echelon manufacturers are mainly ADI and TI, which together account for about 60% of the market share.

l MAXKGO's choice

In order to bring high-quality products and better experience to users, MKBMS is based on the modular BMS of ADI LTC68XX.

ADI is a world-leading analog semiconductor chip company with more than 60 years of long-term cultivation in analog-to-digital and digital-to-analog conversion, power supply, RF, DSP, and some sensor technologies.

Taking Smart BMS Slave Board 18S as an example, the AFE we use is ADI's LTC6813.

l Introduction to ADI LTC6813

Features of the ADI LTC6813 sampling chip:

Sampling range is 0V ~ 5V

Total measurement error less than 2.2mV

Use isolated serial communication

AEC-Q100 Qualified

Passive equalization can reach up to 200mA, and the chip is equipped with PWM control

There are 9 GPIO ports

eLQFP 64-pin package

112.5V withstand voltage

Operating temperature range from –40°C to 125°C

The ADI LTC6813 sampling chip has a maximum of 18 channels of cell sampling and supports daisy chain twisted pair cascading. Its basic architecture is shown in the figure below:

ADI LTC6813 chip sampling function:

The ADC inside the ADI LTC6813 sampling chip will receive the analog voltage signal of the external input cell, so that the digital processing is performed inside the chip:

The ADCV command performs sampling of the battery voltage chip C0 to C18 input

There are 3 ADCs inside the LTC6813-1, and the multiplexer is used to sample the voltage of 18 strings of cells

The figure below shows the voltage data read by ADI’s official Linduino software host computer at room temperature. The data read by each cell is within 2mV of the actual voltage data measured by the actual cell.

ADI LTC6813 is a high-precision lithium battery cell sampling chip with up to 18 sampling channels. This series supports multi-channel sampling and has the advantages of high precision and stable communication.

All software BMS under MAXKGO use ADI's analog front-end chips, aiming to provide customers with a better experience and higher accuracy when monitoring battery data.

ADI's LTC681X series of multi-cell battery monitors can be used to measure the individual voltages of 6, 12, 15 or 18 series-connected battery packs.
Among them, LTC6811 can measure up to 12S, LTC6812 can measure up to 15S, and LTC6813 can measure up to 18S.