The RDDRONE-BMS772 is a standalone BMS Reference Design suitable for mobile robotics such as drones and rovers, supporting 3-6 cell batteries.

Other uses include portable electronics and equipment needing better battery management

• eScooters, ebikes

• high end power tools

• portable medical devices (Pulse oximeter, portable pumps, electric portable refrigerator)

• backup battery system

• outdoor monitoring/measuring equipment

It is an open hardware and software design and useful leverages components used in general purpose automotive and high-reliability industrial applications. The BCC device performs ADC conversion on the differential cell voltages and currents. It is capable of very accurate battery charge coulomb counting and battery temperature measurements.

The NXP MC33772 is a 6 cell BCC. If higher cell counts are required this could be redesigned to daisy chain multiple BCC chips or switch to a larger cell count BCC such as the MC33771. These parts are all automotive grade Li-Ion battery cell controller IC designed for automotive and industrial applications such as HEV, EV, ESS, UPS systems

The BMS772 also features an S32K146/144 automotive grade S32K Microcontroller. These are rugged M4 core processors part of a scalable family of AEC-Q100 qualified 32-bit Arm® Cortex®-M4F and Cortex-M0+ based MCUs

An NTAG5 Boost NFC NFC Forum-compliant I2C bridge is also onboard and appears as an NFC contactless tag to the external world, and interfaces internally in a simple manner similar to an EEPROM for easy secure query of status or setting of parameters using an external NFC device such as a cell phone. In a practical sense this allows an end user to check multitudes of batteries that may be in storage just by hovering their cell phone over them.

An A1007 is an enhanced version of A1006 secure authenticator IC which includes monotonic counters and secure flags. These can be used to prove the battery pack is genuine and has not been tampered with as well as securely count charge cycles, and permanently flag negative events such as over discharge. The Secure Authenticator IC is a secure tamper-resistant authentication IC, which offers a strong cryptographic solution intended to be used by device manufacturers to prove the authenticity of their genuine products

Finally, the BMS communicates with a host such as a Drone Flight Management Unit (FMU) through UAVCAN or I2C/SMBus.

CAUTION - WARNING

Lithium and other batteries are dangerous and must be treated with care.

Important Notice

NXP provides the enclosed product(s) under the following conditions:

This reference design is intended for use of ENGINEERING DEVELOPMENT OR EVALUATION PURPOSES ONLY. It is provided as a sample IC pre-soldered to a printed circuit board to make it easier to access inputs, outputs, and supply terminals. This reference design may be used with any development system or other source of I/O signals by simply connecting it to the host MCU or computer board via off-the-shelf cables. Final device in an application will be heavily dependent on proper printed circuit board layout and heat sinking design as well as attention to supply filtering, transient suppression, and I/O signal quality.

The goods provided may not be complete in terms of required design, marketing, and or manufacturing related protective considerations, including product safety measures typically found in the end product incorporating the goods.

Due to the open construction of the product, it is the user's responsibility to take any and all appropriate precautions with regard to electrostatic discharge. In order to minimize risks associated with the customers applications, adequate design and operating safeguards must be provided by the customer to minimize inherent or procedural hazards. For any safety concerns, contact NXP sales and technical support services. Should this reference design not meet the specifications indicated in the kit, it may be returned within 30 days from the date of delivery and will be replaced by a new kit.

NXP reserves the right to make changes without further notice to any products herein. NXP makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does NXP assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation consequential or incidental damages.

Typical parameters can and do vary in different applications and actual performance may vary over time. All operating parameters, including Typical, must be validated for each customer application by customer’s technical experts.

NXP does not convey any license under its patent rights nor the rights of others. NXP products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other applications intended to support or sustain life, or for any other application in which the failure of the NXP product could create a situation where personal injury or death may occur. Should the Buyer purchase or use NXP products for any such unintended or unauthorized application, the Buyer shall indemnify and hold NXP and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges NXP was negligent regarding the design or manufacture of the part.

The RDDRONE-BMS772 integrates the following functions and features:

• LiPo Battery from 3s to 6s, with stack voltage ranging from 6V to 26V

• ambient temperature range from -20°C to 60°C

• measures battery stack and cell voltages with an accuracy of +/-5mV, battery charge or discharge current up to 200A peak and 90A* DC with an accuracy of 1% for the complete chain and cell temperature with an accuracy of +/- 2°C (including AFE, PCB and NTC inaccuracies)

• active cell balancing during charging

• offers a deep sleep mode (for transportation and storage) with <80μA leakage current, as well as an automatic sleep mode with <200μA current consumption on the battery.

• allows authentication of the battery

• allows diagnostics to verify the safe operation of the battery

• allows CAN, I²C and NFC communication

• implements SWD and JTAG debugging interfaces, works with standard Segger J-Link and other debuggers

• implements DCD-LZ combined debug and uart console interface for use with PX4 DroneCode and HoverGames platforms

Note: The 90A DC maximum current is obtained only when all MOSFETs and heatsinks are mounted. See Power MOSFETs and heatsinks.

To use this BMS772 kit, you will need:

Additional items needed

• LiPo battery pack

  • 3S to 6S with cell balancing connector - Voltage range of 6V to 26V

• Suitable charger for the type of battery

• Soldering iron to configure the board

• External Thermistor temperature sensor with cable and JST-GH 2-pin connector (optional)

• Debugger:

  • Segger J-Link Mini debugger

  • PEMicro universal multilink

  • or other suitable JTAG/SWD debugger

Software tools and sources

• S32 Design Studio for ARM-based MCUs (recommended)

• Alternatively : PX4 or NuttX build environment depending on what code source is used.

• PX4/NuttX board target example code (optional, see Software guide)

Note: The RDDRONE-BMS772 board allows to open the charge circuit when the battery is overcharging , to perform cell balancing and to monitor all cell voltages. Therefore the charger does not need to have a cell terminal connector.

The board is organized as shown in the figures below:

The RDDRONE-BMS772 is a standalone BMS Reference Design suitable for mobile robotics such as drones and rovers, supporting 3-6 cell batteries. Other portable electronics and equipment, such as scooters, power tools, portable medical devices could also benefit from referencing this design. If higher cell counts are required this could be redesigned to daisy chain multiple BCC chips or switch to a larger cell count BCC.

The device performs ADC conversion on the differential cell voltages and currents. It is capable of very accurate battery charge coulomb counting and battery temperature measurements. Additionally, it communicates with a Flight Management Unit (FMU) through UAVCAN and/or an SMBus.

Introduction

As we learn of specific needs for specific use cases they will be noted here:

5V BMS output supply?

PX4 BMS specification and working group discusses the potential requirement to provide 5V power to a vehicle before activating the actual battery power supply main outputs. The intent is to allow something on the host to identify the battery characteristics in advance in order to avoid a catastrophic voltage mismatch.

Conceptually there is a need to supply 5V through the CAN /SBUS connectors to allow a host-side processor to power up and query the smart battery (BMS) for compatibility with the drone. (i.e. do not power up a 12S battery on a drone that only is designed for 3S or 4S)

• This functionality can be tested with the current revision of the board given a few jumper wires to the CAN/SBUS connectors. As built the +5V power is NC

• The 5V supply from the SmartBattery/BMS likely only needs to provide limited current in order to power a small MCU on the host side and not the complete host-side FMU. The small MCU could do the BMS query and then choose to power up the battery if in compliance.

• It needs to be determined how does BMS sleep mode or deep sleep mode should work with this operation.

There are other preventative configurations being discussed such as mechanically preventing incompatible battery packs being inserted, and also using host side configuration resistor to signal to the battery what power/voltage the host expects. These may be discussed on the PX4 working group for BMS.

LED Battery Status indicators

The BMS772 evaluation design includes one RGB led which is intended to flash sequences and colors to show battery status. It has been noted however that some implementations may wish to use 4 LEDS for visual battery gauge status.

• Extra LEDs can be accommodated by using the expansion header

• Alternative option: I2C bus can be also be used to add an local OLED display.

Charging and Balancing

The BMS772 itself doesn't regulate charging current or voltage, and needs a simple CC/CV charger. It can however balance it's own cells and disconnect the load. This situation could be improved by making a charger that talks with the battery over CAN and helps properly manage current and voltage, or even additional circuitry on board to manage this.

Errata

• Rev C of RDDRONE-BMS772 inadvertently does not connect the 5V power from one CAN Connector to the next - Between J3 and J20. If needed a jumper wire can be added between J3-Pin 1 and J20Pin-1. This is corrected on Rev D of the board.

These boards have been designed and optimized for the operating conditions described below. Usage of these boards beyond these conditions can lead to malfunction and damage.

[1] These values are valid for a 4 pairs of power MOSFETs and 4 heatsinks configuration. See Configuring the hardware for more information

Downloading J-link

J-Link Commander is used to flash binaries onto the RDDRONE-BMS772 board. The latest (stable) release of the J-Link Software and Documentation Pack is available at the SEGGER website for different operating systems.

Connecting the programmer to the BMS

The software can only be written to the board using a debugger. The HoverGames drone kit includes a J-Link EDU Mini debugger. To use it, you need to install the J-Link Software Pack.

The debugger can be plugged into the BMS using a small adapter board. This small PCB comes with a 3D printed case that can easily be put together. The J-Link debugger can be connected using an SWD cable. The connectors have to be oriented such that the wires directly go to the side of the board, as shown in the picture below.

While you do not need it right now, the adapter board also has a 6-pin connector for a USB-TTL-3V3 cable, which you can use to access the system console (CLI) of the BMS. The 3D printed case has a small notch on one side of the connector. The USB-TTL-3V3 cable needs to be plugged in such that the black (ground) wire is on the same side as this notch in the case. Make sure the cables are plugged in as shown in the picture below. Connect the 7-pin JST GH to the programming header of the BMS, J19.

Flashing the firmware

A guide for flashing firmware to this board is outlined in one of our consolidated Gitbooks for flashing a multitude of NXP hardware. The link to this Gitbook is below.

Next steps

Once you're done flashing your board, you may continue to the Accessories and tools for development tutorial.

Software example

The software example being developed for the RDDRONE-BMS772 board will use a NuttX Real-Time Operating System (RTOS).

Note: NuttX is a real-time operating system (RTOS) with an emphasis on standards compliance and small footprint. Scalable from 8-bit to 32-bit microcontroller environments, the primary governing standards in NuttX are Posix and ANSI standards.

First start-up

Before first start-up, make sure the board is configured properly:

1. Solder your power in and power out connectors or wires on the J4 and J5 footprints

2. Solder the correct cell terminal connector at the JP1 location. Ensure it is correctly positioned and aligned

3. Configure the board for your application by soldering the corresponding SJxx connectors

4. Configure the board with additional and/or optional components as described in Configuring the hardware to fit the application requirements

Powering the RDDRONE-BMS772 board on and off

Once the board is configured properly (see Configuring the hardware for more details about configuration), it is time to connect the board.

To power on the RDDRONE-BMS772 board, *first* connect the battery to the power input connector (J4) and then the cell terminal connector (JP1). This protects the boards form internal damage due to hot plugging.

Similarly, to disconnect the battery from the board, the cell terminal connector (JP1) should be disconnected first. Then the power input (J4) can be disconnected.

Featured devices

The board features several NXP ICs:

• MC33772: 6-Channel Li-Ion battery cell controller IC designed for automotive and industrial applications such as HEV, EV, ESS, UPS systems. The MC33772 allows ADC conversions on the differential cell voltages and currents as well as coulomb counting and temperature measurements. It features embedded balancing transistors and diagnostics to simplify applications. The device supports standard SPI and transformer isolated daisy chain communication (via MC33664) to an MCU for processing and control

• S32K144: AEC-Q100 certified microcontroller for general purpose automotive applications. The S32K144 features an Arm® Cortex®- M4F core, 512 KB of Flash, CAN/CAN-FD controllers, security module complying with SHE specification and is offered in LQFP-48, LQFP-64, LQFP-100 and MAPBGA-100 packages supporting an ambient temperature range from -40°C up to 125°C

• UJA1169: Mini high-speed CAN System Basis Chip (SBC) containing an ISO 11898-2:201x (upcoming merged ISO 11898-2/5/6) compliant HS-CAN transceiver and an integrated 5V or 3.3V 250 mA scalable supply (V1) for a microcontroller and/ or other loads. It also features a watchdog and a Serial Peripheral Interface (SPI). The UJA1169 can be operated in very low-current Standby and Sleep modes with bus and local wake-up capability

• A1007: A1007 authentication IC is a secure solution built with many tamper resistant features and security countermeasures to deter common invasive and non-invasive attacks

• NTAG5: NXP’s NTAG 5 boost shrinks the NFC footprint while adding AES security, so designers can deliver ultra-compact devices for use in IoT, consumer, and industrial applications

IC board location identifiers

The main ICs featured are listed in the table below:

Connectors

The following figure shows the location of the connectors on the board.

All connectors implemented on RDDRONE-BMS772 are detailed in the table below:

Communication with Flight Management Unit

The RDDRONE-BMS772 board can communicate with a host device such as a PX4 Flight controller (FMU) using the SMBus bus (can also be used as a simple I²C bus, connector J18) or the UAVCAN bus (can also be used as a simple CAN bus, connectors J3 and J20).

Note: For further information about UAVCAN, look for enablement in PX4.io software.

Programming and debug

There are two ways to program and debug the RDDRONE-BMS772 board:

• through the DCD-LZ connector (J19)

• through the JTAG connector (J2)

LED

The RDDRONE-BMS772 implements a programmable RGB LED. Various color combination and blink patterns can be used to indicate the state of the battery and system.

Button

The side button is a wake button, it connects the WAKE pin of the SBC to the ground when pressed. The J22 header placed in parallel of the side button can be used as an alternative if an extended or panel mount button is needed.

External and additional components

External components

An optional external temperature sensor can be added onto the RDDRONE-BMS772 board using connector J1. An example of application for this external sensor can be to monitor the cells temperature inside the battery pack.

Additional components

Some components are included in the design but are not mounted on the RDDRONEBMS772 original board. They are marked "DNP" on the schematics and the BOM. The following table is giving the list of additional components that can be implemented in the design as well as their use:

Test point definitions

The following figure shows the location of the test points on the board.