WM231 Battery Intelligent Board

Table of Contents

Function
Variants
Parts
Programming
External interfaces
Service interfaces
Board view
Schematics

Function

TODO

DJI Intelligent Flight Battery for Mavic Air 2 and Air 2s is a 3500mAh, 11.55V LiPo-3s battery, supporting up to 34 minutes of flight time. The battery also has built-in sensors and LEDs which let you know the status and remaining power. It contains automatic discharge feature to avoid swelling (fully charged LiPo cells release hydrogen), and Permanent Failure feature which disables the battery in case of damage or unexpected behavior of cells.

The battery management system chip (TI BQ9003) communicates with FC directly, through Smart Battery System protocol, with some small modifications introduced by DJI.

The SBS protocol defines battery-related commands to be transferred over SMBus, which in turn is deviced from I2C.

Variants

There are multiple versions of the board.

Marking	Overview
PP001354.05

Parts

Version PP000062.05 components

Marking	Amt.	Pkg.	Function	Specification
BQ9003	1	TSSOP-30	Li-Ion Battery Pack Manager; the specific chip was only made available by TI for a few customers, but it is relatively similar to BQ40Z50. The DJI-modified firmware presents the chip as BQ40z307.

Programming

Chips	Firmware	Description
BQ9003	m1100	Battery Management System chip firmware.

External interfaces

Connectors on the board are:

Marking	Overview
TODO

Service interfaces

The following service pads exist on this board:

Marking	Overview
TODO

Board view

Top of a PP001354.05 board:

Schematics

Functional diagram

flowchart LR
    Connector-BAT((batt<br/>connec<br/>tor))
    subgraph Battery Intelligent board
    direction LR
    BatteryBMS[BQ9003 BMS<br/>Li-Ion pack<br/>manager]
    BattFeedbackR(0.01 Ohm<br/>feedback<br/>resistor)
    EnablePackFET(MOSFET<br/>output<br/>control)
    EnableChargeFET(MOSFET<br/>charge<br/>enable)
    EnableDischargeFET(MOSFET<br/>internal<br/>discharge<br/>enable)
    DischargeR(discharge<br/>resistor)
    BatteryButton(button)
    BatteryLEDs(LED line)
    DischargeR---EnableDischargeFET
    BatteryBMS-- DSG ---EnableDischargeFET
    BatteryBMS-- PCHG ---EnablePackFET
    BatteryBMS-- CHG ---EnableChargeFET
    BatteryButton---BatteryBMS
    BatteryLEDs---BatteryBMS
    end
    subgraph Li-Po cells pack
    direction TB
    BatteryCell1(battery<br/>cell 1)
    BatteryCell2(battery<br/>cell 2)
    BatteryCell3(battery<br/>cell 3)
    BatteryTempSense(NTC<br/>thermistor)
    BatteryCell1===BatteryCell2
    BatteryCell3===BatteryCell2
    end
    BattFeedbackR===BatteryCell1
    BatteryBMS-- VSS ---BatteryCell1
    BatteryBMS---BatteryCell2
    BatteryBMS---BatteryCell3
    Connector-BAT== PACK- ===BattFeedbackR
    BatteryBMS-- SRn ---BattFeedbackR
    BatteryBMS-- TS ---BatteryTempSense
    EnableDischargeFET===BatteryCell3
    EnablePackFET===EnableDischargeFET
    EnableChargeFET===EnableDischargeFET
    Connector-BAT== PACK+ ====EnablePackFET
    Connector-BAT== PACK+ ====EnableChargeFET
    Connector-BAT-- SMBus ----BatteryBMS

Loading

Thick lines are the ones transferring high power. Feedback resistor for measuring current is inserted into negative line, while all the MOSFET switches are within positive line. The three Li-Po cells are connected in series, so that the voltage sums up.

The output connector includes SMBus lines from the Battery Management System chip, which allow to exchange packets described in Smart Battery Specification, as well as some DJI-specific extensions.

The charge level, as well as errors and faults detected within the BMS, can be shown on four LEDs. Specifics of how the interface and the buttons work, as well as extensions to the SBS protocol, require implementation within the BMS firmware. Therefore, the firmware is not a stock TI version, but a modification of TIs firmware code by DJI engineers.

Hardware schematics

No schematics available.