WM220 Battery Intelligent Board

Table of Contents

Function
Variants
Parts
Programming
External interfaces
Service interfaces
Board view
Schematics

Function

DJI Intelligent Flight Battery for Mavic is a 3830mAh, 11.4V LiPo-3s battery, supporting up to 27 minutes of flight time. The battery also has built-in sensors and bright LEDs that 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 BQ30Z55) is queried for data by a small micro-controller (TI MSP430) through a Smart Battery System protocol. That micro-controller sends updates to the FC in regard to current battery status, through UART interface.

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

Variants

There are multiple versions of the board.

Marking	Overview
P01690.06

Parts

Version P01690.06 components

Marking	Amt.	Pkg.	Function	Specification
BQ30Z55 6CT G4 AQGF	1	TSSOP-30	Integrated 2-Series, 3-Series, and 4-Series Li-Ion or Li-Polymer Cell Battery Pack Manager and Protection; the specific chip was only made available by TI for a few customers, but it is very similar to BQ30Z554. Also, its spec can be found in various places (sluu852a.pdf).	description applc.note
1C530l Prm 1708 C1 9632	4		Nexperia N-channel 30V 1.55mOhm logic level MOSFET in LFPAK using NextPower technology	description
MSP430 G2755 TI A66K CF0Q G4	1		MSP430 ultra-low-power sensing and measurement MCU	description
WM9 71	2	SOT23
VS6 Z	1	SOT23
K7K DN	5	SOT23
14D	1	SOT25
R004	2		SMD Resistors
101	2		SMD Resistors
201	3		SMD Resistors
330	8		SMD Resistors
T4	3
AC	7

Programming

Chips	Firmware	Description
BQ30Z55		Battery control chip; it has firmware, but that is not publicly available.
MSP430	m1100	Small micro-controller which queries the BQ30Z55 for battery status and sends the information to Flight Controller.

External interfaces

Connectors on the board are:

Marking	Overview
10-slab EXT PWR	External connector of the battery; provides power input and output, and serial interface.

External connector of the battery

Here is the connector pinout:

Pin	Label	Function
1	RXD	UART receive
2	PACK-	Ground reference for PACK+
3	PACK-
4	PACK+	+12.92V from battery cells
5	PACK+
6	PACK+
7	PACK+
8	PACK-
9	PACK-
10	TXD	UART transmit

Service interfaces

The following service pads exist on this board:

Marking	Overview
TODO

Board view

Top of a P01690.06 board:

Bottom of the P01690.06 board:

Top of another P01690.06 board:

Bottom of the P01690.06 board:

Top of a third P01690.06 board, with better visible copper connections:

Schematics

Functional diagram

flowchart LR
    Connector-BAT((batt<br/>connec<br/>tor))
    subgraph Battery Intelligent board
    direction LR
    BatteryMCU[MSP430 MCU<br/>Battery<br/>interface<br/>control]
    BatteryBMS[BQ30Z55 BMS<br/>Li-Po pack<br/>manager]
    BattFeedbackR(0.02 Ohm<br/>feedback<br/>resistor)
    BatteryButton(button)
    BatteryLEDs(LED line)
    BatteryMCU-- GPIO ---BatteryButton
    BatteryMCU-- GPIO ---BatteryLEDs
    EnablePackFET(MOSFET<br/>output<br/>control)
    EnableChargeFET(MOSFET<br/>charge<br/>enable)
    EnableDischargeFET(MOSFET<br/>internal<br/>discharge<br/>enable)
    DischargeR(discharge<br/>resistor)
    DischargeR---EnableDischargeFET
    BatteryBMS-- DSG ---EnableDischargeFET
    BatteryMCU-- SMBus ---BatteryBMS
    BatteryBMS-- GPOD ---EnablePackFET
    BatteryBMS-- CHG ---EnableChargeFET
    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-- UART ---BatteryMCU

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 Battery Management System chip is not designed to have any user interface, so that is handled by the additional micro-controller. The MCU communicates with BMS using the protocol described in Smart Battery Specification, over SMBus interface. The charge level, as well as errors retrieved from the BMS, can be shown on attached line of four LEDs. The MCU can also read button state, and ask the BMS to start or shutdown the power delivery.

The battery does no make use of chemical fuse support built into BQ30Z55 - the FUSE pin is pulled down through a resistor.

Hardware schematics

No schematics available.