AN2344 Power Management - Battery Charger with Cell-Balancing and Fuel Gauge Function Support.pdf

AN2344
Power Management - Battery Charger with Cell-Balancing and Fuel Gauge
Function Support
Author: Oleksandr Karpin
Associated Project: Yes
Associated Part Family: CY8C27x43, CY8C29x66
Software Version: PSoC® Designer™ 5.1
Associated Application Notes: AN2180, AN2314
AN2344 integrates cell-balancing and fuel gauge methods into a multi-cell battery charger. The application is designed for
battery packs with two, three, or four Li-Ion or Li-Pol cells in a series. It includes dedicated PC-based software for real-time
viewing and analysis of the charge, cell-balance and fuel gauge processes. The application can be used as a complete
battery pack management system for notebooks, medical and industrial equipment, and other, similar applications.
Contents
Introduction
Introduction .......................................................................1
Regulator Topologies ........................................................3
Buck Converter.............................................................3
Buck-Boost Converter ..................................................4
SEPIC...........................................................................4
Device Schematic..............................................................5
Multi-Cell Battery Charger Firmware .................................9
Conclusion ........................................................................9
Appendix A: Charge, Discharge, Cell-Balance and Fuel
Gauge Profile Examples.................................................. 10
Worldwide Sales and Design Support ............................. 14
This Application Note combines the cell-balancing method,
“Cell Balancing in a Multi-Cell Li-Ion/Li-Pol Battery Charger,”
and the fuel gauge method, “Li-Ion/Li-Polymer Battery
Charger with Fuel Gauge Function” with a multi-cell battery
charger into a complete battery pack management system.
This battery pack management system provides:





Correct charging of two, three, or four Li-Ion or Li-Pol
cells in a series with one or more cells in parallel.
Protection from overcharge, deep discharge, and short
circuit conditions.
Temperature detection that shuts off the charging or
discharging processes when battery temperature is
outside the allowed temperature range.
Cell balancing in the battery pack.
Calculation of fuel gauge parameters including absolute
capacity, state of charge, and run and charge time
remaining.
This Application Note also includes dedicated PC-based
software developed to allow real-time viewing and analysis
of the charge, cell-balance, and fuel gauge
www.cypress.com
Document No. 001-15223 Rev. *B
1
Power Management - Battery Charger with Cell-Balancing and Fuel Gauge Function Support
Figure 1 shows the battery pack management system
schematic.
Figure 1. Battery Pack Management Schematic
Q5
Q6
Battery Pack
Management System
PACK+
R4
CELL4
Q4
R3
Charger,
Monitor,
Safety,
Fuel Gauge,
Cell Balance
Software
Load
CELL3
Q3
R2
CELL2
Q2
R1
CELL1
Q1
PSoC
PACK-
A safety circuit, internal to the PSoC® device, controls the
back-to-back MOSFET switches, Q5 and Q6. These
switches are opened to protect the pack against fault
conditions such as overcharge, deep discharge, and overcurrent. The resistor, Rsense, is a current-sense resistor
that is in the battery pack current path. The fuel gauge
accumulates the measured current to determine the
available capacity of the battery pack. The cell-balancing
circuit is represented by R1 and Q1) to R4 and Q4. These
transistors and resistors dissipate energy and control the
amount of balancing current to provide cell balancing in the
battery pack.
The unique architecture of the PSoC device provides an
integrated hardware solution for a multi-cell battery charger
with minimal external components at a very affordable price.
It also provides flexible microcontroller-based cell-balancing
and fuel gauge algorithms. You can upgrade algorithms with
the latest charge, cell-balance, or fuel gauge technologies
with a firmware change.
This system uses its own COM-based protocol for
communication between the battery pack management
system and the host device. You can implement the SMBus
protocol in the PSoC firmware, if desired.
The characteristics and software capabilities of the multi-cell
Li-Ion and Li-Pol battery charger with cell-balance and fuel
gauge functions are listed in Table 1.
Rsense
The battery back management system provides correct
battery pack charge and discharge processes. The only
external connections required are the external power supply
connections to PACK+ and PACK-.
Table 1. Specifications for Multi-Cell Li-Ion and Li-Pol Battery Charger
Item
Specification
Battery Charger
6..25 V
Power Supply Voltage
Power Consumption

Active Mode
30 mA
1
8 mA

Sleep Mode
Battery Temp. Measurement Range (Software
-20..60 °C
Configurable)
Battery Current Measurement Error (Not Calibrated)
5%
Battery Voltage Measurement Error (After
0.5%
Calibration)
Temperature Measurement Absolute Error
1 °C
User Interface
2 Buttons and 2 State LEDs
PC Communication Interface
RS232
PC Communication Speed
115,200 baud
Cell-Balancing Parameters
1. During charge phase
Cell-Balancing Algorithms
2. During discharge phase
www.cypress.com
Document No. 001-15223 Rev. *B
2
Power Management - Battery Charger with Cell-Balancing and Fuel Gauge Function Support
Item
Specification
Cell-balance circuit resistors nominal
Cell-balance interval parameter
Minimum balance voltage value for charge phase
Cell-Balancing Configuration Parameters
Minimum balance voltage value for discharge phase
Minimum charge current value when cell balancing is allowed
Voltage value of the middle charging state for the discharge
phase
Minimum Balance Voltage Value for Charge Phase
Equal to the voltage measurement error value (15 mV – 30 mV)
Equal to the voltage measurement error value (15 mV – 30 mV)
Minimum Balance Voltage Value for Discharge Phase
plus the internal impedance error (10 mV – 30 mV)
Fuel Gauge Parameters
Fuel Gauge Battery Capacity Monitoring Method
Coulomb counter-based fuel gauge

Absolute capacity (ACR)

State of charge (SOC)

Runtime remaining in active mode
Fuel Gauge Calculation Parameters

Runtime remaining in suspend mode

Full-charge time remaining

Rapid-charge time remaining

Temperature
Fuel Gauge Correction

Discharge rate

Cell aging (fuel gauge learning charge cycle)
Fuel Gauge State of Charge (SOC) Measurement
1-3%
Error
1
Note The project in this Application Note is not optimized for power consumption. This value can be greatly decreased.






Regulator Topologies
Buck Converter
There are two basic types of power regulators: linear
regulators and switching regulators. The most popular of
the switching regulator topologies are:
The buck converter or step-down converter can only step
voltage down from a higher level to a lower level. Figure 2
shows a buck converter schematic.





Figure 2. Buck Converter Schematic
Buck Converter (Step-Down Converter)
Q
L
POWER+
Boost Converter (Step-Up Converter)
Cin
D
Cout
Buck-Boost Converter
Flyback Converter
Battery
Single-Ended Primary Inductive Converter (SEPIC)
This section describes the buck, buck-boost, and SEPIC
topologies because they are most frequently used in
battery chargers.
Advantages of the buck converter:

Low complexity
Disadvantages of the buck converter:


www.cypress.com
There is a path from the battery pack to the Power+
input through the buck switch MOSFET body diode.
Therefore, an additional blocking diode in the path is
needed.
If the MOSFET ever shorts there is no way to limit the
current into the battery. Therefore, an additional
protection device (fuse) must be used.
Document No. 001-15223 Rev. *B
3
Power Management - Battery Charger with Cell-Balancing and Fuel Gauge Function Support
Buck-Boost Converter

Buck-boost converters produce a regulated output voltage
either less than or greater than the input voltage. When
the input voltage is higher than the output, the converter
acts as a buck. When the input is lower than the output,
the converter boosts. Figure 3 shows a buck-boost
converter schematic.


Figure 3. Buck-Boost Converter Schematic
The output stage rectifier diode is used as a reverse
blocking diode.
It uses only a single switch.
If switch Q1 shorts, the input voltage power supply is
shorted as well and the battery pack is disconnected
from the external power supply (in contrast to buck
and buck-boost converters).
Q1
L
POWER+
Cin
Disadvantages of the SEPIC:
D2
D1
Cout
Q2
R
Battery
Advantages of the buck-boost converter:


The input voltage can be less than or greater than the
output voltage.


It has higher switch/diode peak voltages and currents
compared to the other topologies.
Two external components, an inductor with two
windings and coupling capacitor, are needed.
In this application, the technical advantages of the SEPIC
outweigh the disadvantages. If you need a battery charger
with only step-down capability, the simple buck converter
(step-down regulator) is preferred.
The output stage rectifier diode is used as the reverse
blocking diode.
Disadvantages of the buck-boost converter:


If the MOSFET ever shorts there is no way to limit the
current into the battery (similar to the buck converter).
Two switches and two diodes are needed so that the
output power is not inverted.
SEPIC
The Single-Ended Primary Inductive Converter (SEPIC)
uses a two-winding inductor and a coupling capacitor to
store and transfer energy. Figure 4 illustrates the SEPIC
schematic.
Figure 4. SEPIC Schematic
D2
POWER+
Cin
Cout
L
1
1
Cc
Battery
Q1
Advantages of the SEPIC:


The input voltage can be less than or greater than the
output voltage.
It has good capacitive primary-to-secondary isolation.
www.cypress.com
Document No. 001-15223 Rev. *B
4
Power Management - Battery Charger with Cell-Balancing and Fuel Gauge Function Support
Device Schematic
This Application Note uses the device structure, battery
pack parameter measurement techniques, and PSoC
internal structure from, “Cell Balancing in a Multi-Cell LiIon/Li-Pol
Battery
Charger.”
The
temperature
measurement technique used is the one explained in
AN2314, “Thermistor-Based Temperature Measuring in
Battery Packs.”
Figure 5 and Figure 6 show the complete multi-cell battery
charger schematic.
A signal from the pulse width modulator PWM_DRIVE
goes to the high-speed MOSFET driver U1. This driver
chip provides MOSFET Q1 with high slew rate regulation
from the low current PWM_DRIVE signal. The
PWM_DRIVE switch frequency was set close to 100 kHz.
When switch Q1 is turned on, the current through the
inductor L1 will ramp up at a rate of Vin/L1. When the
inductor L1=L2 is coupled, the current through the inductor
L2 will ramp at the same rate. Therefore, the switch
current Q1 is equal to the sum of the inductor currents
while the switch is on. The input current in the SEPIC is
continuous. When switch Q1 turns off, the path for current
is from the input through the inductor L1 and the coupling
capacitors (C8, C10, C12-C14) to the output. Another path
for current flow exists through inductor L2 to the output.
Therefore, the sum of L1 and L2 currents flow to the
output. This output current also replenishes the output
capacitors (C3-C6) while the switch is off. The output
capacitors provide the output current flow while the switch
is on. This smoothes the output current pulses from the
SEPIC.
The cell-balancing circuit is represented by MOSFETs Q2Q5 and balancing resistors R8, R12, R15, R20. The
resistors R9, R13, R17, capacitors C15, C17, C21, and
diodes D5-D7 allow a TTL signal from the PWM_BAL to
control the MOSFETs Q2-Q4. The lower transistor Q5 is
directly controlled by the PSoC device port; a high level
turns it on, low level turns it off.
The resistive network (R5, R7, R10, R11, R14, R16, R18,
R19, R21, R22, R24-R27, R30) and the reference voltage
Vbias from the divider on R36 and D13 changes the
battery current, voltage, and temperature signals to levels
that are suitable for the PSoC device. The 100 mΩ resistor
R29 is a current-sense resistor that is in the battery pack
current path.
The multi-cell charger user interface uses two buttons,
SW1 and SW2, to control some of the process and two
LEDs to display internal status:
www.cypress.com




Green LED lit – Charge phase
Yellow LED lit – Discharge phase
Both LEDs lit – Error state
Both LEDs off – Idle state
SW1 is used to turn the device on and off. Switch SW2 is
used for test purposes. Holding switch SW1 on and
pressing switch SW2 allows you to choose the number of
batteries connected in series in the battery pack. The
result is shown on the LEDs and on the PC software. The
result is also stored to the internal Flash memory of the
PSoC device.
Linear regulator U3 provides the processor power supply
from a higher level voltage. As an alternative, you can use
a regulated step-down converter from the internal switch
mode pump (SMP) as shown in AN2180, “Using the PSoC
Switch Mode Pump in a Step-Down Converter.” To use
this device as a battery pack management system you
should use a switching regulator with very little power
consumption. An external voltage supply is applied to the
connector J4. Switch SW3 allows the device to be
disconnected from the external power supply. Two diodes
in the diode array D10 allow the processor to operate
during the charge phase from the external power supply
and during the discharge phase from the battery pack
power supply.
The external load is connected to the connector J3 LOAD.
The diodes D8 and D9 are used to provide an
uninterruptible power supply for the LOAD connector in a
manner that is similar to that of D10 for the processor. The
switch on transistors Q6 and Q7 allow the power supply to
be disconnected from the LOAD to protect the battery from
deep discharge. This switch is optional and can be
removed to reduce total device cost. Often, deep
discharge protection is implemented in the batteries
themselves by means of a dedicated protection IC. The
board ground level is set to the external ground level
POWER- before the current-sense resistor. As a result,
only the charge battery pack current and the total battery
pack discharge current are passed through the currentsense resistor. These are used to supplement the battery
fuel gauge function in the PSoC software.
The user module placement and internal connectivity of
the PSoC device are shown in Figure 7. The PWM_BAL is
configured on the clock source from CPU 32 kHz (internal
low speed oscillator). This gives the PWM_BAL user
module the ability to work during processor sleep mode.
The rest of the configuration is very similar.
Document No. 001-15223 Rev. *B
5
Power Management - Battery Charger with Cell-Balancing and Fuel Gauge Function Support
Figure 5. Multi-Cell Battery Charger Schematic – CPU, Cell Balancing, and Measuring Equipment
C1
R1
POWER+
20
1n 50V
C2
L1
L2
D2
1
1
MBR360
. .
1u 25V
R4
BAT+
+ C3
C4
C5
C6
2u 25V
2u 25V
1u 25V
10
22u 25V
1:1 70uH
+ C7
D4
U1 MOSFET driver
C11
6
12V
4.7u
0.1u
3
C12
VCC
20N06HD
GND
R6
2
DRIVE
4
IN1
OUT1
IN2
OUT2
C8
Q1
C10
7
R5 200K 0.1%
C13
5
V4
10
C14
C9
0.01u
MC34152
1u 25V
R7
R8
40K 0.1%
100
Vbias
Q2
IRLML2502
C15
VCC
U2
10n
Vcc
Vi1
V3
Vref
J1
VCC
1
2
3
4
5
V1
1
2 P0[7]
3 P0[5]
4 P0[3]
P0[1]
5
6 P2[7]
7 P2[5]
8 P2[3]
P2[1]
BAL2
BAL1
BAL3
Tbat
9
SMP
10
11 P1[7]
12 P1[5]
13 P1[3]
P1[1]
BAL4
TX
CALIBRATION
14
CALIBRATOR/DEBUG
BAL4
P0[6]
P0[4]
P0[2]
P0[0]
P2[6]
P2[4]
P2[2]
P2[0]
Xres
P1[6]
P1[4]
P1[2]
P1[0]
28
D5
R9
BAT54S
1M
R11 200K 0.1%
V3
27
26
25
24
Vi2
V4
V2
BAT_GND
23
22
21
20
C16
0.01u
LED_GREEN
LOAD_EN
LED_YELLOW
EXT_POWER
R10
R12
40K 0.1%
100
Vbias
Q3
IRLML2502
C17
19
18
17
16
15
SW2
DRIVE
SW1
R13
J2
BAT4
D6
BAL3
1M
10n
BAT3
BAT54S
R14 200K 0.1%
V2
BAT2
C18
0.01u
Vss
CY8C27443_DIP28
R16
R15
40K 0.1%
100
BAT1
GND
TERMO
1
2
3
4
5
6
7
8
9
BAT_CON
VCC
VCC
C19
25pF
Y1
Vbias
Q4
IRLML2502
C21
C20
25pF
D7
BAL2
10n
XTALin
XTALout
R17
1M
BAT54S
R19 200K 0.1%
V1
32,768kHz
C22
0.01u
Vref
R18
R20
40K 0.1%
100
Vbias
Q5
IRLML2502
BAL1
R21
R22
1M 1%
1M 1%
R23
1M
Vi2
Vi1
R24 200K 0.1%
BAT_GND
C23 0.1u
C24
0.01u
R25
R26
200K 1%
R29
200K 1%
R27
40K 0.1%
Vbias
POWER-
Tbat
R30
10K 1%
100mOh 1%
Vref
www.cypress.com
Document No. 001-15223 Rev. *B
6
Power Management - Battery Charger with Cell-Balancing and Fuel Gauge Function Support
Figure 6. Multi-Cell Battery Charger Schematic – Power Supply and User Interface
Q6
IRLML6402
D8
J3
1
2
POWER+
R2
LED_YELLOW
R32
D9
BAT+
470
LED
LOAD
20K
R3
MBR360
POWER+
R38
D1
LED_GREEN
D3
470
R28
LED
20K
56K
R33
Q7
BC817
LOAD_EN
330R
EXT_POWER
R34
R31
10K
20K
POWERSW1
SW3
+
J4
D11
POWER+
1
2
+ C25
SW1
C30
SW2
MBR360
100u 25V
0.1u 25V
POWER 20V DC
SW2
POWERVCC
D10
BAT+
Close to PSoC
VCC
R35
U3 HT7550-1
1
IN
OUT
R36
3
VCC
1K
130 1W
POWER+
BAT54C
Vbias
+
C26
C27
+ C28
C29
D13
22u
0.1u
BAS16
C31
0.1u
100u 25V
www.cypress.com
0.47u 25V
Document No. 001-15223 Rev. *B
7
Power Management - Battery Charger with Cell-Balancing and Fuel Gauge Function Support
Figure 7. Internal User Module Placement and Configuration
www.cypress.com
Document No. 001-15223 Rev. *B
8
Power Management - Battery Charger with Cell-Balancing and Fuel Gauge Function Support
Multi-Cell Battery Charger Firmware
Conclusion
The multi-cell battery charger firmware is separated into
several modules that serve distinct functions:
This multi-cell Li-Ion/Li-Pol battery charger with cellbalancing and fuel gauge technology supports single cell
batteries or battery packs with two, three, or four Li-Ion or
Li-Pol cells in series. It allows you to use an external
supply with a wide voltage range either less than or
greater than the battery pack voltage.







Performing measurements
Regulating the battery charge process and timer
functions
Performing the Li-Ion or Li-Pol battery charging
algorithm
Checking the charge termination conditions
Performing fuel gauge and cell-balance algorithms
Storing calibration settings to the PSoC device Flash
memory
Transmitting debug data
It provides dedicated PC-based software for real-time
viewing and analysis of the charge, cell-balance and fuel
gauge processes.
The unique architecture of the PSoC device provides an
integrated hardware solution for a multi-cell battery
charger with flexible microcontroller-based, cell-balance
and fuel gauge algorithms requiring minimal external
components at a very affordable price. The device can be
used as a complete battery pack management system for
notebooks, medical and industrial equipment, and other,
similar applications.
Figure 8. Multi-Cell Battery Charger Photograph
www.cypress.com
Document No. 001-15223 Rev. *B
9
Power Management - Battery Charger with Cell-Balancing and Fuel Gauge Function Support
Appendix A: Charge, Discharge, Cell-Balance and Fuel Gauge Profile Examples
Figure 9. Charge and Discharge Manager Profile
www.cypress.com
Document No. 001-15223 Rev. *B
10
Power Management - Battery Charger with Cell-Balancing and Fuel Gauge Function Support
Figure 10. Fuel Gauge Information Profile
Learning
Cycle End
Empty Capacity
at 16 °C
www.cypress.com
Document No. 001-15223 Rev. *B
11
Power Management - Battery Charger with Cell-Balancing and Fuel Gauge Function Support
Figure 11. Cell-Balancing Activity Profile
Battery Voltages
V1,V2,V3,V4
With Charge Interrupt
Imbalance Value
Initial Voltage
Imbalance
Value
Voltage Imbalance
Value after First
Charge/Discharge
Cycle
www.cypress.com
Document No. 001-15223 Rev. *B
12
Power Management - Battery Charger with Cell-Balancing and Fuel Gauge Function Support
Document History
Document Title: Power Management - Battery Charger with Cell-Balancing and Fuel Gauge Function Support – AN2344
Document Number: 001-15223
Revision
ECN
Orig.
Change
of
Submission
Date
**
1034485
YARD_UKR
05/02/2007
*A
3285106
ANBI_UKR
06/16/2011
*B
4429522
RJVB
07/03/2014
www.cypress.com
Description of Change
Added new spec
Updated to latest PSoC Designer.
Updated document to new template.
Updated template.
Document No. 001-15223 Rev. *B
13
Power Management - Battery Charger with Cell-Balancing and Fuel Gauge Function Support
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Document No. 001-15223 Rev. *B
14
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