Li-Ion, Li-Pol Charger Using MC9S08QD4 - Freescale

Freescale Semiconductor
Application Note
Li-Ion, Li-Pol Charger Using
MC9S08QD4
by: Stanislav Arendarik
RTAC Roznov, Czech Republic
1 Introduction
In the present time, there is a continuously growing
amount of battery-powered appliances, Li-Ion and Li-Pol
batteries are frequently used. They are best suited to
power supply requirements of used microcontrollers. It is
possible to combine several battery cells in series to
reach higher supply voltage. But most of applications use
single-cell configuration. The batteries are charged by
standard wall adapters or directly through USB interface
of the PC. Charging is ensured by the dedicated battery
charger in an appliance. This charger maintains safe
charging conditions and proper, full charge of the
battery cell. On the other side, a microcontroller in an
appliance can replace a dedicated battery charger too.
This can lower the final cost of the whole appliance. This
microcontroller needs only several added external
components to build the whole charger. These
components are needed in most of chargers, specially
powered by universal wall AC/DC adapter. On the other
side, the microcontroller can boost the Li-Ion battery
voltage (from 2.8 to 4.2 V) to higher voltage with tight
© Freescale Semiconductor, Inc., 2009. All rights reserved.
Document Number: AN3825
Rev. 0, 03/2009
Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2 Li-Ion and Li-Pol Battery Description . . . . . . . . . . . . . . . . 2
3 Charger Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4 DC/DC Boost Converter Description . . . . . . . . . . . . . . . . 6
5 Software Implementation. . . . . . . . . . . . . . . . . . . . . . . . . 6
6 Application Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
6.1 Schematic Description. . . . . . . . . . . . . . . . . . . . . . . 8
6.2 Software Description . . . . . . . . . . . . . . . . . . . . . . . . 8
7 Conclusion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Li-Ion and Li-Pol Battery Description
tollerance, for example +5.0 V or more, to supply some other circuits in the application. Both parts —
the Li-Ion and Li-Pol charger and boost converter implemented in MC9S08QD4 MCU will be discussed
in this application note. The software for both implementations can be used in any other stand-alone
application too. As an example of this implementation, the metronome application for musicians is
presented with detailed schematic. The whole software pack is in the AN3825SW.zip file.
2 Li-Ion and Li-Pol Battery Description
Li-Ion batteries employ a graphite material used in conjuction with a lithiated transition metal oxide,
such as lithium cobalt oxide. The electrolyte consists of a lithium salt dissolved in a mixture of organic
carbonates. During the charge and discharge reaction, lithium ions move across the cell between the carbon
and metal oxide electrodes.
A lithium battery cell typicaly consists of a spiral-wound roll of two composite electrodes separated by a
microporous film, containing the electrolyte solution. This all is sealed in a metallic case. The operating
voltage ranges from 2.8 to 4.2 V per cell. This very useful voltage level combined with high energy density
has lead to rapid grow of use in a wide range of electronic appliances, mainly in mobile phone market and
as battery packs for notebooks. But these batteries are very useful in all applications, where a power supply
is about 3.3 V — a level mostly used in microcontroller applications.
The lithium-polymer (Li-Pol) batteries are very similar to the Li-Ion technology. They have the same
properties as Li-Ion type, but a slightly higher energy density, and they can be manufactured as very thin
cells, whilst retaining the performance and cost profile of Li-Ion.
The Li-Ion and Li-Pol batteries have some important advantages over a previously used NiCd or
NiMH types:
They have no memory effect.
They have a very low self-discharge.
Another advantage is simpler charging than nickel-based batteries.
There is an absence of topping and trickle charge.
They have a higher energy density.
Li-Ion and Li-Pol batteries can share the same charger.
On the other side you have to pay attention to:
You have to maintain a proper charging vo ltage level; maximum is 4.20 V per cell.
You have to avoid deep discharging under 2.7 V per cell.
You have to avoid exposing the battery to high temperatures.
You have to avoid excessive heating of battery wh ilst charging or discharging (higher than +45 °C).
2
Li-Ion, Li-Pol Charger Using MC9S08QD4, Rev. 0
Freescale Semiconductor

3 Charger Description
Li-Ion, Li-Pol Charger Using MC9S08QD4, Rev. 0
Charger Description
The main goal was to use as simple configuration as possible, and meet all requirements for safe and proper
charging of Li-Ion battery. The next aim was to reach a very low price of the whole solution. The software
in the MCU controls the charging to maintain charging sequence defined by the manufacturer. This
sequence is known as CCCV type. This means constant current and constant voltage shape. It is shown
in Figure 1.
4,2V
Imax
Imin
Constant Current Constant Voltage
Ubat
Ibat
Time
Figure 1. CCCV Charging Characteristic
During the first part of the charging process named as “constant current,” the battery voltage grows. At the
end of this part the battery is charged up to 70 % of the nominal capacity. The charging processor must
look up to actual battery voltage to avoid over-voltage of the battery. The maximal construction limit is
4.30 V, thus the real charging limit is 4.20 V. The charging current during this period is defined by the
battery properties. The standard mobile phone battery can be charged by 1 C current, the larger types
(for example the 18650 type) usually 0.8 C or less. The C means current in mA, equal to capacity in mAh;
for example 700 mA for capacity of 700 mAh. There are Li-Pol batteries on the market that can be charged
by a much higher current.
The next part of charging process is named “constant voltage”. In this state the charging processor must
maintain a constant voltage of 4.20 V on the battery. The charging current decreases and battery is going
to a full charge. When the charging current reaches the low limit, which is about 3 % of rated charging
current I max , the battery is considered as fully charged and charging process is finished.
Freescale Semiconductor 3

Charger Description
The schematic of this charger solution is shown in Figure 2. This charger is based on the standard buck
DC/DC converter structure. The power P-MOSFET is controlled by a PWM signal from the MCU.
The duty cycle of the generated PWM signal with the inductor determines the charging current. The MCU
measures the actual battery voltage by an ADC converter input ADC1. The mentioned QD4 type of MCU
includes a 10-bit ADC, which is sufficient of accurate measurement of the voltage of charged
Li-Ion battery. It is possible to use the next free ADC inputs to measure temperature of the battery using
the internal temperature sensor too. On the other side, if you design this charger for a certain range of
battery capacity, you can set the maximal charging current by limit of PWM duty cycle.
4
+5V
+
C1
Vdd
Vss
D1
MCU
MC9S08QD4
PWM
ADC1
ADC2
ADC3
Control
MOSFET
Figure 2. Simplified Charger Schematic
It is a very simple configuration, while the power supply voltage will be only +5.0 V, for example from
the USB port of PC. If you need to use a higher input voltage, the low-cost low-power linear voltage
regulator must be used to power the MCU only. All other parts are powered by input voltage higher than
V DD of MCU. The final version shown in Figure 3 can be used with input supply in range up to 16 V DC.
There are several small changes, when compared to the previous simple schematic of charger. The MCU
is powered from a dedicated +3.3 V linear voltage regulator. This voltage level maintains a proper
functionality, when the whole charger is powered from an external power source in the range from 5 V
to 16 V. The upper limit depends on the properties of used components — capacitor C8, C9, power
MOSFET Q2, and voltage regulator U1. The values of the inductor L1, capacitor C8 and C9 depend on the
used power source and level of the charging current. They can be reduced in accordance to final design.
Values on the schematic are usable for charging current up to 300 mA.
Li-Ion, Li-Pol Charger Using MC9S08QD4, Rev. 0
C3
R
D2
L
C4
+
+
Battery
Cell
Freescale Semiconductor

D1
2 1 Vin1
L1
D2 SS12
NTGS3455T1
SS12
2 1
SWin
SWout 1 2
Bat+
U1
R3
100UH
3
Vdd 20.0K
IN OUT
1
C9 +
R1
D3
220UF
C4
1.0K Q2 SS12
+ C8 C8 C1
L78L33ACU C2
1.0UF
R5
47UF 47UF
10.0K
0.10UF
1.0UF
GND
Vin
1
2
3 1
5
6
4
J5
2 1
GND
3
2
1
2
PJ-007
J3
2
+
t
-
1
2
3
T
R7 10.0K
U2
BKGD
RST
Figure 3. Detailed Charger Schematic
Li-Ion, Li-Pol Charger Using MC9S08QD4, Rev. 0
Charger Description
Freescale Semiconductor 5
HDR 1X3
C5
1.0UF
R6
20.0K
8
7
6
5
PTA0/ADC1P0
PTA1/ADC1P1
PTA2/ADC1P2
PTA3/ADC1P3
VDD 3
1
PTA5/RST/IRQ
PTA4/BKGD
2
J1
1 2
3 4
5 6
C7
0.1UF
VSS
J4
BDM
MC9S08QD4CSC
4
2
1
Q1
BSS138LT1G
2 3
1
R4
10.0K
C6
0.1UF
LED_EN
D4
1 2
R2
R8
D5
1 2
MVC5474C
180 OHM
180 OHM
MVC5474C

DC/DC Boost Converter Description
4 DC/DC Boost Converter Description
The DC/DC boost converter converts the battery cell voltage to a higher desired output voltage.
This converter utilizes a very simple schematic shown in Figure 4.
6
Battery
Cell +
+4V
+
C1
Figure 4. DC/DC Boost Converter
The switcher N-MOSFET is controlled by a PWM signal from a microcontroller (MCU) of the application.
Diode D is a standard Schottky type, capacitors C1 and C2 are low-ESR aluminium electrolyte types. In
the real application the output voltage +5 V powers the MCU. In this case this MCU can simply measure
this level, and directly set the PWM duty cycle to maintain a proper regulation of the output voltage +5 V.
Values of the capacitors C1, C2, and inductor L are selected in accordance to output current and voltage
ripple requirements. The capacitor values in the range from 47 µF to 330 µF are sufficient in
most applications. The inductor value is in the range from 22 µH to 330 µH. You need to pay attention to
select the proper size of this inductor in accordance to output current. In this configuration it is very easy
to reach the output voltage in tolerance of ±0.1 V or better. You can use this converter for any other output
voltage level in real range. Then the output-voltage divider must be used to measure the output voltage,
because this level can be out of input range of the MCU’s analog-to-digital converter (ADC).
5 Software Implementation
The Li-Ion battery charger and DC/DC boost converter can be used as stand-alone application, but they
can be implemented in the real application as an added software pack. In case you want use it as
a stand-alone charger, you can use schematic shown in Figure 3. It can be corrected in accordance to user
requirements — it can tightly fit the dedicated battery. Then you can reach the lowest cost possible. In case
you want to use a whatever wall adapter in voltage range up to 16 V DC, you can use the schematic shown
in Figure 3. This design is made as an example for testing purposes and it works very well.
The DC boost converter can be used as a stand-alone application too. It can be implemented in a low-cost
MCU with PWM and ADC capability. For example it can be the MC9S08QD4.
6 Application Example
L
Control
Both the charger and the converter can be used as an added software in any other application too. One small
design was made as an example for this implementation — it is an accurate metronome for musicians. The
software is implenemted in a new type of MCU — the MC9S08SG8. The whole schematic is shown in
Figure 5.
MOSFET
+
C2
Li-Ion, Li-Pol Charger Using MC9S08QD4, Rev. 0
D
+5V
Freescale Semiconductor

Application Example
Li-Ion, Li-Pol Charger Using MC9S08QD4, Rev. 0
Freescale Semiconductor 7
Figure 5. Metronome Schematic
Vbat
+Vin
Charger
Battery Converter
Repro-
+Vin
SW1
SW2
SW3
GND
+5V
LCD_Vo
LCD_RS
LCD_RW
LCD_EN
LCD_D4
LCD_D5
LCD_D6
LCD_D7
LCD_Vo
+5V
Vext
+5V
GND
BKGD
RESET
LCD_RS
LCD_RW
Charger
LCD_EN
LCD_D7
LCD_D6 LCD_D5
LCD_D4
Vext
SW3
SW2
SW1
Repro-
Repro+
Battery
Converter
BKGD GND
RESET
+5V
+5V
+5V
Repro+
GND
REPRO
Battery Charger
DC/DC Boost Converter
R2
10k
R2
10k
R4
100k
R4
100k
J2
J2
L2
470uH
L2
470uH
+ C5
220uF
+ C5
220uF
SW3
SW3
D4
RB051L-40
D4
RB051L-40
R6
10k
R6
10k
R1
1k
R1
1k
R10
1k
R10
1k
R7
1k
R7
1k
A
B
SW1
A
B
SW1
Q5
NTJD4105C
Q5
NTJD4105C
D2
1N4148WX
D2
1N4148WX
Q1
2SA2056
Q1
2SA2056
+ C7
220uF
+ C7
220uF
R12
1k
R12
1k
SW4
SW4
L1
33uH
L1
33uH
DS1
PC1602-D
DS1
PC1602-D
VSS
1
VDD
2
Vo
3
RS
4
R/W
5
E
6
DB0
7
DB1
8
DB2
9
DB3
10
DB4
11
DB5
12
DB6
13
DB7
14
A_BKL+
15
K_BKL-
16
C6
100n
C6
100n
J3
BDM
J3
BDM
1 2
3 4
6
5
R5
1K
R5
1K
R11
10k
R11
10k
Q4
NTJD4105C
Q4
NTJD4105C
R8
1k
R8
1k
C1
100n
C1
100n
R3
330k
R3
330k
D1
RB051L-40
D1
RB051L-40
Q3
BSR14
Q3
BSR14
R9
10k
R9
10k
C11
100n
C11
100n
Q2
BC847AL
Q2
BC847AL
+
C8
3300uF
+
C8
3300uF
J1
DC_POWER_JACK
J1
DC_POWER_JACK
1
2
3
BT1
Li-Ion
BT1
Li-Ion
C4
100n
C4
100n
+
C3
470uF
+
C3
470uF
C2
100n
C2
100n
D3
RB051L-40
D3
RB051L-40
U1
MC9S08SG8
U1
MC9S08SG8
RESET
1
BKGD
2
Vdd
3
Vss
4
PB7/EXTAL
5
PB6/XTAL
6
PB5/T1Ch1/SS
7
PB4/T2Ch1/MISO
8
PC3/AD11
9
PC2/AD10
10
PC1/AD9
11
PC0/AD8
12
PB3/MOSI/AD7
13
PB2/SCK/AD6
14
PB1/TxD/AD5
15
PB0/RxD/AD4
16
PA3/SCL/AD3
17
PA2/SDA/AD2/ACO 18
PA1/T2Ch0/AD1/AC-
19
PA0/T1Ch0/AD0/TCLK/AC+
20
SW2
SW2

Application Example
The application provides:
Li-Ion battery charger
DC/DC boost converter
LCD display driver
Sound generator
Speaker driver
6.1 Schematic Description
The heart of this shematic is the MC9S08SG8 MCU. This MCU maintains all functions needed. It can be
powered with voltage ranging from +2.7 to +5.5 V. The main power source is one-cell Li-Ion battery BT1.
It is in the center of the schematic. The parts on the left belong to Li-Ion charger, and parts on the right
belong to DC/DC boost converter. The next part is a standard LCD display (powered by +5 V) and sound
driver — full bridge MOSFET powered by +5 V with a small speaker as a load. A relatively large
capacitance C8 is used, because of high-current impulse load of +5 V line. When your application doesn’t
require as high impulse load, the small capacitance C7 is sufficient in most applications.
Standard bipolar transistors are used instead of presented MOSFET; they were “on the hand” and
functionality is the same. After powerup by switching the main switch SW1, the MCU starts to run
on battery voltage of about 3.6 to 4 V. This voltage is too low for proper functionality of the LCD.
The MCU measures its own power supply and starts to run the DC/DC boost converter software.
The +5 V power line rises to its level, and then it is possible to run the application software. The DC/DC
boost converter software runs in the background and maintains the stabilized power supply of +5 V.
The MCU software continuously senses the external voltage V ext on C2. If the external voltage in range
from +6.5 V to +16 V is connected to DC power jack J1, then the Li-Ion charger software starts to run.
This routine measures the actual battery voltage and external applied voltage and charges the battery until
full charged. Then the charging process is terminated.
6.2 Software Description
The application software uses accurate time intervals generated by RTI interrupt in the MCU.
It is important that this time interval serves as the synchronization point for all three software routines to
be able to run concurrently. A test was made with a period of RTI interrupt from 5 ms to 30 ms and all
applications ran properly. The accurate RTI period depends on the actual application. The state diagram of
this application is shown in Figure 6. It is possible to add some other tasks to a software loop and make the
RTI interrupt period setting comply with requirements of all tasks to achieve a proper functionality.
8
Li-Ion, Li-Pol Charger Using MC9S08QD4, Rev. 0
Freescale Semiconductor

7 Conclusion
START
Power UP sequence,
RTI initialization
Measure Vdd line, start
DC/DC boost converter,
wait for +5V stabile
RTI period
count = X1?
N
RTI period
count = X2?
N
RTI period
count = X3?
N
Y
Y
Y
Figure 6. State Diagram
Run the application
Run the charger
Run the converter
Li-Ion, Li-Pol Charger Using MC9S08QD4, Rev. 0
Conclusion
This application note is an example how to implement Li-Ion or Li-Pol charger and DC/DC
boost converter into real customer application. All tasks and functions are implemented in
application software. These applications were tested on a very simple low-cost MCU of the S08 family
(MC9S08QD4, MC9S08SG8). The MCUs utilize internal peripherals as 10-bit ADC, real-time interrupt
module RTI, PWM module, and internal bandgap reference (constant V ref ). It is possible to implement
these algorithms to whichever S08 family of MCUs, which comprise mentioned internal peripherals. The
whole application source code with a description inside is provided as the AN3825SW.zip file.
Freescale Semiconductor 9

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Document Number: AN3825
Rev. 0
03/2009
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