[PDF] 3~6 Cells Battery Management System Based On BQ76925+

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Application Report

SLUA707 - March 2014

1 3 to

6 Cells Battery

Management System Based On

bq76925 + MSP430G2xx

2 Richard Tang, Andy He Power FAE, MCU FAE / Shenzhen China

ABSTRACT

This application report describes how to use bq76925 and MSP430G2xx2 to implement a high-accuracy digital battery-management solution, which can support a complete pack monitoring, balancing, protection , and gas gauging system for 3 to 6 series cell Lithium- Ion / Polymer battery. This solution is designed to focus on power tool projects, while it can be also a reference design for other similar applications. Please send questions or comments about this template to

Richard Tang (

mailto:Richard- tang@ti.com) or Andy He (mailto:Andy-he@ti.com).

SLUA707

2 3 to 6 Cells Battery-Management System Based On bq76925 + MSP430G2xx2

Contents

1 Features ........................................................................................................................................ 3

2 Introduction .................................................................................................................................. 3

3 Description ................................................................................................................................... 4

3.1 Major Hardware Functions and Design Guidelines ................................................................. 4

3.1.1 Cell Voltage Sense Circuits ......................................................................................... 4

3.1.2 External LDO .............................................................................................................. 5

3.1.3 SC Protection and Wake-up Circuits ........................................................................... 6

3.1.4 Voltage and Current Measurement ............................................................................. 7

3.1.5 Drivers ........................................................................................................................ 8

3.1.6 Precharge Control ....................................................................................................... 9

3.1.7 Load Removal Detection ............................................................................................. 9

3.2 MCU Software Description ................................................................................................... 10

3.2.1 MSP430G2xx2 Software Flow .................................................................................. 10

3.2.2 Accuracy ................................................................................................................... 15

3.2.3 Low-power Mode ...................................................................................................... 16

3.2.4 Over Temperature (OT) ............................................................................................ 17

3.2.5 Under Temperature (UT) ........................................................................................... 18

3.2.6 Over Current (OC) .................................................................................................... 19

3.2.7 Short Current (SC) .................................................................................................... 21

3.2.8 Over Voltage (OV) .................................................................................................... 24

3.2.9 Under Voltage (UV) ................................................................................................... 25

Appendix A. user.h ............................................................................................................................ 26

Figures

Figure 1. Overall Schematic ........................................................................................................... 4

Figure 2. Cell Voltage Sense Circuits ............................................................................................

5

Figure 3. External LDO .................................................................................................................... 6

Figure 4. SC Protection and Wake-up Circuits .............................................................................. 7

Figure 5. Voltage and Current Measurement ................................................................................. 7

Figure 6. Drivers .............................................................................................................................. 8

Figure 7. Precharge Control ........................................................................................................... 9

Figure 8. Load Removal Detection ............................................................................................... 10

Figure 9. Mainloop Flow................................................................................................................ 11

Figure 10. Measuring Flow ............................................................................................................. 12

Figure 11. Function Flow ................................................................................................................ 14

SLUA707

3 to 6 Cells Battery-Management System Based On bq76925 + MSP430G2xx2 3

1

Features

To implement a

high-accuracy digital battery-management solution, bq76925 + MSP430G2xx2 can supp ort a complete pack monitoring, balancing, protection, and gas gauging system for 3 to

6 series cell Lithium-Ion / Polymer battery. This solution is designed to focus on power tool

projects, while it can also be a reference design for other similar applications. 2

Introduction

The bq769

25 is a dedicated analog front e

nd (AFE) for 3 to 6 series cell application that provides 3 analog outputs that allow a microcontroller to easily monitor cell voltage, current, and temperature. Cell voltages are level-shifted, scaled, and multiplexed to the VCOUT pin. Cell current is monitored through a sense resistor placed in series with the cell stack. The voltage across the sense resistor is amplified and driven to the VIOUT pin. The VTB pin supplies a switched bias to stimu late a thermistor network for temperature measurement. The bq76925 supplies a

3.3-V regulated output to power the MSP430G2xx2 and an accurate 3.3-V reference

voltage for the MSP430G2xx2 analog-to-digital converter (ADC). The AFE also includes integrated ce ll balancing FETs that are under control of the MSP430G2xx2. Finally, the on-board comparator of the AFE signals an overcurrent condition to the MSP430G2xx2 for fast fault response. The MSP430G2xx2 series is an ultra-low-power microcontroller with one built-in 16-bit timer, a fast 10 -bit ADC with integrated reference, built-in communication capability using the universal serial communication interface, and up to 24 I/O pins. The architecture, combined with five low- power modes, is optimized to achieve exten ded battery life in portable measurement applications. The MSP430G2xx2 application circuit is provided to read the analog signals from the bq76925 and let the user create custom firmware based on the application code. With the AFE of bq76925, the MSP430G2xx2 is evaluated as the host to control bq76925 by I 2 C of USI module, the MSP430G2xx2 can read the data of analog signals from bq76925 by ADC10.Then the MSP430G2xx2 can easily monitor individual cell voltages, pack current, and temperature to achieve battery charge and discharge management. Although it is only a 10 -bit ADC result for the MSP430G2xx2, bq76925 can calibrate it into a high-accuracy value with the particular compensated algorithmic of correction factors. For example, the ADC10 value deviation of cell voltage does not exceed 5 mV, which can strongly make this solution outstanding in this field requirement. To make this solution more competitive, the MSP430G2xx2 is selected for its advantages of low power and low cost. The user can choose the part number of the MSP430G2xx2 from MSP430G2x32/G2x52, as there are eight part numbers for the different configurations, like flash size, Comparator_A+.

More software functions mean more

flash size is need. The user can choose the right part number based on the necessary functions of the MSP430G2xx2.

SLUA707

4 3 to 6 Cells Battery-Management System Based On bq76925 + MSP430G2xx2

3

Description

This application note, which can help designers evaluate the bq76925 + MSP430G2xx2 battery- management system, discusses the important setup and operation of the module, and contains schematics, bill of materials, and printed circuit board layout. Before designing a battery- management system based on the bq76925 + MSP430G2xx2 solution, designers are advised to read the bq76925 and MSP430G2xx2 data sheet.

3.1 Major Hardware Functions and Design Guidelines

VC5 Q1

ZXTP25040DFH

RIN6 47
Q16

BSS84P

Q17

2N7002E

LED1/XIN

LED0/XOUT

LED2/COM2

R20 2K Q10

IRFS3206PBF

C16

1uF/25V

C170.1uF/50V

D17 LED D16 LED R27 10M D18 LED

R33471

R35471

VC2

R36471

R52 2M R26 100R
R5 3.3K R7 3.3K CB1

CIRCUIT BREAKER

12 R8 10K

VDRVPACK+

DVCC CB10

CIRCUIT BREAKER

12 Y1 32768

C2012p

C14 0.1uF C21 12p C8 470pF
VIOUT VCOUT R10 10K RIN5 47
C9 0.1uF NTC1 10K CIN6 1uF THERM Q11

IRFS3206PBF

RIN4 47

C180.1uF/50V

RIN3 47
C7

0.33uF/50V

R28 2.2M R17 1K D13 18V RIN2 47
CIN5 1uF PAD4 PACK- 1 1 RIN1 47
Q5

BSS84P

R13 1M SW1

EVQPE504K

R18 2.2M PAD3 PACK+ 1 1 Q8

2N7002ER211K

R24 5.1M CHG DVCC VDRV D6

CD4148WT

MCU D11

CD4148WT

SDA C22 0.1uF VC1 R22 1K PAD1 BATT+ 1 1 SW2

EVQPE504K

CIN4 1uF C23

1000pF

R2 100R
+C2

10uF/50V

VC3 Z1

AZ23C5V6-7-F

3 12

R42100R

R44100R

R48 1M R46 1M

R45100R

R43100R

J21 SMBUS 12 34
56
78
910

U2MSP430G2452IPW20

P1.2/A2

4 P2.2 10

P1.1/A1

3

P1.5/A5

7

P1.0/A0

2

P1.4/Vref/A4

6

XOUT/P2.7

18 DVCC 1

P1.3/A3

5 DVSS 20

SDA/P1.7

15

RST/NMI

16 P2.0 8

XIN/P2.6

19 P2.1 9 P2.3 11 P2.4 12 P2.5 13

SCL/P1.6

14 TEST 17 CIN3 1uF R120 R110 C10 DNP C11 DNP C5 10uF CB3

CIRCUIT BREAKER

12 CB4

CIRCUIT BREAKER

12 C4 0.1uF J5

TestPoint

1DVCCSCL

J6

TestPoint

1 DVSS J10

TestPoint

1 J11

TestPoint

1SDA J7

TestPoint

1VREF J12

TestPoint

1THERM

J8

TestPoint

1VCOUT

DISP/LOADCHK

J13

TestPoint

1VIOUT

PRECHG

J22 SBW 1 2 3 4 5 SDA SCL CB6

CIRCUIT BREAKER

12 CB7

CIRCUIT BREAKER

12 DVCC RST R47 47K
R53 1M TCK R41 331

LED3/COM1D20

LEDR38471

CIN2 1uF

LED1/XIN

CB8

CIRCUIT BREAKER

12

LED0/XOUT

CB9

CIRCUIT BREAKER

12 VC4

LED2/COM2

LED3/COM1

RSENS1

0.002/1W 1%

RSENS2

0.002/1W 1%

R34 200R
R37 1M R31

3.3KR32

1M Q13

BSS84P

Q12

2N7002E

D22

MBR0540T1G

D19 LED CB2

CIRCUIT BREAKER

12 ALERT DVCC CB5

CIRCUIT BREAKER

12 J23 COM 1 2 3 J24quotesdbs_dbs14.pdfusesText_20

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