AN73468 PSoC 3 and PSoC 5LP Single-Cell Lithium-Ion (Li-ion) Battery Charger.pdf

AN73468
PSoC® 3 and PSoC 5LP - Single-Cell Lithium-Ion (Li-ion) Battery Charger
Author: Archana Yarlagadda, Rajiv Badiger
Associated Project: Yes
Associated Part Family: All PSoC 3 and PSoC 5LP
Parts
®
Software Version: PSoC Creator™ 3.3 or Higher
Related Application Notes: AN55102
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AN73468 explains a single-cell Lithium-Ion (Li-ion) battery charger implementation using PSoC 3 or PSoC 5LP. Two
types of implementations — linear and switching type are supported. An attached PSoC Creator project, which
includes a charge display tool, demonstrates Li-ion battery charging.
Contents
Introduction
Introduction .......................................................................1
Li-Ion Battery Charging Profile ..........................................1
Project Implementation......................................................3
PSoC Creator Project ........................................................4
Battery Parameter Measurement .................................4
Charging Algorithm in Firmware ...................................7
External Current Control Circuit....................................8
Battery Protection Logic ...............................................9
Calibration ....................................................................... 11
Test Setup and Results ................................................... 12
USB Communication .................................................. 12
Charge Display Tool ................................................... 12
Conclusion ...................................................................... 12
Appendix A: Buck Circuit Component Selection.............. 13
Appendix B: Schematic and Bill of Materials for
Switching Method of Current Control ......................... 15
Appendix C: USB Driver Installation ................................ 17
Appendix D: Software Tool Installation and Setup .......... 18
Appendix E: Alternative Implementation Options with
Tradeoffs ......................................................................... 20
Biasing Thermistor using IDAC .................................. 20
Over Voltage and Over Current Protection ................. 20
Battery Current Control with PWM ............................. 21
Document History ............................................................ 22
Li-ion batteries are used in a wide range of systems such
as cameras, cell phones, electric shavers, and toys. The
charging circuit for the batteries can either be an integral
part of the system (online charging) or an external plug-in
circuit (offline charging). With its wide range of devices,
PSoC offers a cost-effective solution in both segments.
And with its configurable digital and analog features,
PSoC 3 or PSoC 5LP enables implementation of other
critical tasks required in the system.
Consider a case of an electric shaver that uses Li-ion
battery charger logic and a motor to drive the shaver
blade. Both of these major tasks can be run from a single
PSoC 3 or PSoC 5LP device, which results in lower cost
and small PCB size. Small size is important in batteryoperated (portable) systems.
Li-Ion Battery Charging Profile
The charge profile used for charging is the constant
current (CC) – constant voltage (CV) method. The Li-ion
batteries have different states of charging, based on the
voltage of the battery as shown in Figure 1. These are:



www.cypress.com
Pre-charging (tstart) or activation (tact)
Rapid charge or fast charge

Constant current (trapid)

Constant voltage (tconst_voltage)
Charge complete
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PSoC® 3 and PSoC 5LP - Single-Cell Lithium-Ion (Li-ion) Battery Charger
value while the battery voltage is at Vfull, the charging is
considered complete and the current is reduced to zero.
Figure 1. Charge Profile for Li-ion Battery
This multi-stage process helps to remove the effects of
battery source impedance or any track or connector
resistance between the charging system and the battery.
The constant current stage features rapid charge until a
safest operating voltage (full charge voltage) is reached.
The constant voltage stage ensures that the voltage value
being read corresponds to the battery voltage and does
not include voltage drop across any series resistances.
Besides voltage, temperature of the battery should also be
monitored for safety reasons.
Figure 2 shows a simplified block diagram of a battery
charger system.
Figure 2. Block Diagram of Battery Charger
If the battery voltage is less than the activation voltage
(Vactivation), the charging process starts with the pre-charge
stage where small amount of current (Iactivation- typically
10% of the battery capacity) is provided to check if the
battery is in good condition. Time limit (tstart) is kept low for
this stage. If the battery voltage does not rise above
Vactivation in tstart time, battery is considered faulty and
charging is stopped.
When the battery voltage rises above Vactivation, activation
stage is entered where charging is continued with the
same amount of current. This brings the battery voltage to
the rapid charging voltage level. If the battery does not rise
to the specified rapid charge voltage within the activation
timeout period tact, the battery is considered dead. The
activation stage is used when the Li-ion batteries are
completely discharged. In most cases, the batteries are
not completely discharged and they go directly into the
rapid charge stage.
In the rapid charge stage, the charge current is kept equal
to the capacity specified for the battery. This constant
current is applied until the battery reaches its specified full
charge voltage (Vfull). In this region, the accuracy of
voltage measurement is very important for the safety of
the battery. The tolerable error in measurement is
generally less than ±1% of Vfull. This application note uses
calibration scheme to achieve this target.
After the constant current stage, the battery goes to the
constant voltage stage. In this stage, the battery voltage is
maintained at a constant level. This requires a decrease in
the charging current as the time progresses. When the
current value reaches the termination current (Itermination)
www.cypress.com
Supply
Current
control circuit
charging current
+
Charging
Algorithm
Battery
parameter
measurement
T
-
Battery Pack
The battery parameter measurement senses the three
parameters of the battery: voltage, current, and
temperature. These should be maintained within the
battery safe range. The logic for controlling these
parameters is implemented in the charging algorithm,
which can be applied in hardware or in a combination of
firmware and hardware. The output of the charging
algorithm changes the charge current through the external
current control circuit. The current control circuit can be
either linear or switching. This application note shows the
firmware implementation of both the linear and switching
type of charge control. The benefit of a firmware
implementation is its adaptability to change in the charging
profiles.
The complete block diagram and the functions of each
block are explained first, followed by explanation of the
PSoC Creator implementation.
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PSoC® 3 and PSoC 5LP - Single-Cell Lithium-Ion (Li-ion) Battery Charger
Project Implementation
for additional features related to the battery protection. For
more information on each of these blocks and the
components used, see PSoC Creator Project. The
external current control can be either linear or switching
type of implementation. The switching circuit is shown in
Figure 3, and the linear circuit is explained in External
Current Control Circuit section. The rest of the circuit and
firmware implementation apply to both methods.
Figure 3 shows the overall block diagram for
implementation of the Li-ion battery charger with a PSoC 3
and PSoC 5LP device.
The implementation is divided into the measurement,
charging algorithm, and external current control blocks as
explained earlier. Additionally, a protection block is added
Figure 3. Block Diagram for Li-ion Battery Charger with PSoC
Q1
L1
To Battery
MOSFET
Gate Driver
(ADP3120)
D2
Q2
C1
D1
FDC6561
External current control
DC
3.3V / 5V
regulator
PSoC 3 / PSoC 5LP
Vdd
Battery
protection
logic
GND
IDAC
Charge Control
Algorithm
RIRef1 RVRef
Vbatn
RIRef2
+
RTp
CPU
RVS1
-
Vbatp
Battery Pack
Battery parameters
measurement
Timers
RTm
T
Ibatn
PWM
Generator
RTRef
ADC
RVS2
Vbatp
Vbatn
Vbatn
Ibatp
Ibatn
Ibatp
RFilt
RTp
RTm
Debug
Logic
VDAC
Ibatn
CFilt
RS
RTp
USB
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PSoC® 3 and PSoC 5LP - Single-Cell Lithium-Ion (Li-ion) Battery Charger
PSoC Creator Project
This section guides you through implementation of the
design in PSoC 3 and PSoC 5LP. The complete block
diagram is shown in Figure 3, and this section explains
each function in detail along with the PSoC components
selected to implement them.
Battery Parameter Measurement
Figure 4 shows the battery parameter measurement
function in PSoC 3 and PSoC 5LP. The three parameters
of interest — voltage, current, and temperature are
measured using an ADC.
Figure 4. Top Design: Battery Parameter Measurement
The Delta-Sigma ADC component is multiplexed to
measure
multiple
parameters.
For
temperature
measurement, the standard “Thermistor Calculator” is
used in the project. The details about this custom
component are provided in application note AN66477 ®
PSoC 3 and PSoC 5LP Temperature Measurement with
Thermistor. The bias required for this component is
generated using the VDAC8 component.
Figure 5. DelSig ADC Configuration
The CPU configures the AMUX channel and reads the
ADC to get the parameter values. The configuration of
each of these components is described in the following
sections.
Delta-Sigma ADC
In the project, the ADC is used to measure battery voltage,
charging current, and temperature. Figure 5 shows the
ADC_DelSig component configuration.
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PSoC® 3 and PSoC 5LP - Single-Cell Lithium-Ion (Li-ion) Battery Charger
When multiplexing multiple channels to the ADC, set the
ADC to Multi-Sample mode. This mode resets the ADC
modulator every time a sample is taken, so that the
readings for one channel do not affect another channel.
The resolution is set to 16 bits with a measurement input
range of ±2.048 V. Based on these settings, the resolution
obtained for voltage, current, and temperature is shown in
Table 1.
Figure 6. AMux_ADC Configuration
Table 1. Resolution of Parameters Based on ADC Settings
Parameter
Voltage
Resolution
62.5 uV / K
Notes
K is the scaling factor of the
resistor potential divider
connected across the battery.
R vs 1
K=
R vs 1 + R vs 2
In this design, the following
resistors are used:
R vs 1 = 499 kΩ
The channel selection is done in firmware. Table 2 shows
the allocation of channels.
Table 2. Channel Allocation for AMUX
R vs 2 = 392 kΩ
Channel
In this design, RS is 0.2 Ω. This
gives current resolution of
0.312 mA.
0
Voltage
Pin_VBatp
Pin_VBatn
1
Current
Pin_IBatp
Pin_IBatn
2
Temperature
Pin_RTp
Pin_VBatn
3
Temperature
Pin_RTm
Pin_VBatn
Parameter
This gives measurement
resolution of 142 uV.
Current
62.5 uV / RS
Temperature
±0.01 °C
Range: 0 to 50 °C
RTref = 10 kΩ ± 1% at 25 °C
The conversion rate is set to 9800 samples per second,
which can be changed depending on your application
requirement.
In the ADC settings, differential measurement is used,
because it removes the effect of common mode voltage.
Common mode voltage can be a PCB trace voltage drop
because of current, induced noise, or offsets.
Port Connections
+
-
VDAC
The project uses the VDAC8 component to generate the
reference voltage required for the thermistor temperature
measurement. Figure 7 shows the configuration of this
component.
Figure 7. VDAC8 Configuration
The DelSig ADC has an input buffer at its differential input.
The gain and mode of this buffer are configurable. For this
project, “Buffer Gain” is set to 1 and “Buffer Mode” is set to
level shift. Level shift mode enables the measurement of
voltages close to PSoC ground rail. This is required for
current measurement because the voltage across the
current sense resistor is very close to the PSoC ground.
For example, with a 0.2 Ω current sense resistor and
30 mA termination current, voltage across the sense
resistor is 6 mV.
Note These settings are applicable for all the parameters
measured. For details of other parameters, see the DelSig
ADC component datasheet.
AM U X
The project uses the AMUX component to multiplex
different inputs to the ADC. Figure 6 shows the
configuration of the AMux_ADC. Four channels are
defined, each with a differential type.
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PSoC® 3 and PSoC 5LP - Single-Cell Lithium-Ion (Li-ion) Battery Charger
The VDAC output range is set to 4.08 V. This gives a
resolution of 16 mV/bit. The VDAC output voltage is used
to bias the Thermistor. Make sure that you do not set the
VDAC8 output higher than what the ADC DelSig can
measure. Note that the ADC measurement range is set to
±2.048 V. In this project, the VDAC output is set to 2.0 V.
This voltage is divided across the reference resistor and
the thermistor.
External Circuitry
This section gives details about the external components
required for the battery parameter measurement. These
components appeared in previous block diagrams and in
Figure 9.
Figure 9. External Connections - Measurement
+
Thermistor Component
The Thermistor Calculator component is a standard
Creator component used with this project.
RTp
RTRef
RTm T
RVS1
-
Vbatp
Battery
Pack
RVS2
Vbatn
Ibatp
RFilt
Ibatn
This component requires one resistor for reference
connected in series with the Thermistor. The component
takes the ADC readings of both the thermistor voltage and
the reference resistor voltage to find the temperature.
The configuration of this component is shown in Figure 8.
Figure 8. Thermistor Configuration
In this design, external reference resistor RTRef of 10 kΩ is
connected in series with the Thermistor. Thermistor
resistance values at different temperature values are
provided for calibration. This design uses Thermistor
NTSD1XH103FPB. Its resistance values at three different
temperature values (0 °C, 25 °C, and 50 °C) are given to
the component for calibration.
For more information about this component, see
®
application note AN66477 – PSoC 3 and PSoC 5LP
Temperature Measurement with Thermistor.
www.cypress.com
CFilt
RS
Voltage Sense
Voltage sense is implemented by attenuating the battery
voltage to the range of the ADC, using the resistors - RVS1
and RVS2. The sum of these resistor values should be
greater than 100 kΩ to minimize the loss of charge current
through the resistors. The present design uses RVS1 of
499 kΩ and RVS2 of 392 kΩ.
Current Sense
The current sense is implemented by using a small value
resistor on the low side of the battery. The RS resistor
shown in Figure 9 is used for current sense. The value of
this resistor should be such that the maximum current
allowed through the battery is less than the power rating of
the resistor. There is a trade-off between the signal
integrity (requires higher RS) and power dissipation
(requires lower RS). Typically, for a charge current of 1 A,
a resistor value less than 0.5 Ω can be used to prevent
more than 0.5 W of power dissipation. The actual number
for the allowed power dissipation will depend on your
target application specification. This design uses RS of
0.2 Ω.
The voltage across RS is filtered using an RC low-pass
filter to remove switching noise. You must set the cut-off
frequency of the filter to be much lower than the switching
frequency.
Temperature Sense
The VDAC gives a constant voltage to the thermistor (RT)
and its reference resistance (RTRef). This method has the
benefits of offset and gain error cancellations. A
Thermistor component is used for the implementation of
the temperature measurement. The reference resistor
RTRef value should be close to the thermistor resistance at
the middle of the temperature range.
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PSoC® 3 and PSoC 5LP - Single-Cell Lithium-Ion (Li-ion) Battery Charger
An alternative method of implementation is to use an IDAC
for constant current implementation. In this method, a
constant current is passed through the thermistor, and the
change in voltage due to change in thermistor resistance
is noted. Appendix E: Alternative Implementation Options
with Tradeoffs shows this option and its implementation.
Charging Algorithm in Firmware
In the project, the CPU has the following major tasks:


Run the calibration algorithm


Update the state machine
Read the battery voltage, charging current, and
temperature
Update the PWM duty cycle
Figure 10 shows the firmware flowchart.
Figure 10. Flowchart for Battery Charging
Start
Initialize all
components
Calibration
activated?
Yes
No
Get the scale
factor from the
Flash location
Calculate scaling
factor and update
Flash location
No
Scan time flag is
set?
Yes
Read the battery
voltage, current
and temperature
Update the
charging state
machine
Update the PWM
duty cycle
Execute other
tasks(if present)
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PSoC® 3 and PSoC 5LP - Single-Cell Lithium-Ion (Li-ion) Battery Charger
The following is a description of the state machine for the
attached project, as shown in Figure 11.
Figure 11. Charger State Machine Diagram
reset
No Battery
Battery
Error
Const
Voltage
Activation
As explained earlier, there are two major stages in battery
charging: Constant current (CC) and Constant voltage
(CV) stage. Both stages require control of charging
current. This is achieved by controlling the voltage applied
across the battery. Two methods can accomplish this:


Initialization
Charge
Complete
External Current Control Circuit
Wait For
Temperature
Rapid
Charge
Linear regulator
Switching regulator
Linear Regulator
This method involves controlling the bias of the series
pass transistor (Q2 in Figure 12) to control the current to
the battery. The PWM signal is fed to the external RC lowpass filter to get an average DC voltage to bias transistor
Q1. Controlling the duty cycle of PWM controls the
average DC voltage at the output of the filter. This controls
the collector current of Q1 and, therefore, the battery
charging current (collector current of Q2). Transistor Q2
also prevents reverse powering of PSoC and reverse
current into the supply.
This type of implementation supports limited charging
current, for a reasonable cost of the pass transistor. It has
the benefit of lower footprint than the switching method.
The state machine is updated based on the voltage,
temperature, and current charging state of the battery.
Figure 11 shows the state machine for the charging
process.

No Battery state: The battery is not connected and
the charge current is set to zero.

Initialization state: The battery is connected, the
voltage is less than the activation voltage, and the
charge current is set to activation current.

Activation state: The battery reaches the activation
voltage within some time limit. In this state, the charge
current is maintained at the activation value.

Rapid Charge state: The voltage is at the rapid
charge voltage. The charge current is set to the
highest possible value.

Constant Voltage state: The battery voltage is at the
rated value, and the current is slowly decreased, while
ensuring the battery voltage remains at the rated
voltage. The current in this state decreases until the
termination current is reached.

Charge Complete state: In this state, battery is
completely charged. Charging process is stopped.
Figure 12. Linear Current Control Circuit
Q2
Supply VDC
Battery charging
current
PSoC
PWM
Q1
R
C
Switching Regulator
This method involves the use of buck or boost switching
regulator. This application note uses a buck type switching
regulator to supply the required current through the
battery. It is implemented using an external MOSFETFDC6561 and Gate driver ADP3120.
During this sequence of steps, if the battery voltage,
current, or temperature is out of the specified limits for that
state, the state is set to “Battery Error” and the charge
current is set to zero to protect the battery.
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PSoC® 3 and PSoC 5LP - Single-Cell Lithium-Ion (Li-ion) Battery Charger
Figure 13. Switching Buck regulator Circuit
on how to select the external components for a buck
regulator, see Appendix A: Buck Circuit Component
Selection.
Supply VDC
PSoC
PWM
PWM
MOSFET
Gate
Driver Driver
Enable
Q1
Q2
L1
D1
To Battery
D2
C1
Diode D1 is connected across the lower MOSFET to give
a freewheeling current path during the dead time when
both MOSFETs are off. This dead time is set by the
MOSFET gate driver. Diode D2 is used to prevent current
from the battery from flowing back to the supply when the
supply voltage is less than the battery voltage.
A switching regulator is useful for high-charging currents
(>1A) due to its high efficiency.
PSoC 3 / PSoC 5LP gives a PWM signal of 500 kHz to the
external MOSFET gate driver. The gate driver has two
outputs, which drive the gate terminal of two N-channel
MOSFETs configured for the buck regulator. Values of
inductor L1 and output capacitor C1 are chosen for a
desired ripple current and voltage. For more information
Battery Protection Logic
Figure 14 shows the over voltage and over current
protection logic implementation in PSoC 3 / PSoC 5LP.
The output of the comparators controls the PWM
generator as shown.
Figure 14. Top Design - Battery Protection
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PSoC® 3 and PSoC 5LP - Single-Cell Lithium-Ion (Li-ion) Battery Charger
When the battery voltage or battery charging current
exceeds the limit set using IDAC8_Ref, the output of
comparator goes to zero and is latched in “sticky 0” latch,
which disables the PWM. It also causes an interrupt to the
CPU to take the required action.
ControlReg_BlockComp is a control register used to
enable or disable the latching of comparator output.
Comparator output is latched on the rising edge of the
PWM_Sync signal. The PWM_Sync signal is generated in
such a way that the switching spikes will not trigger the
OV/OC protection. During ADC channel switching,
comparator output latching is disabled by writing a zero to
the ControlReg_BlockComp control register to prevent
misfire.
External Circuitry
This section includes the external resistor circuit required
along with the internal setup for over voltage and over
current implementation.
Figure 16. External Circuitry - Battery Protection
To generate the PWM signal, a custom component
“DitheredPWM” is created. It provides higher resolution
than the regular PWM component. The configuration of
each of the components used in this implementation is
explained below:
IDAC8
IDAC8_Ref is used to generate the reference current
required to obtain the battery current and voltage limits.
The settings for the IDAC are shown in Figure 15. IDAC is
configured in sourcing mode in 2.04 mA range. Its value is
set based on the threshold voltage required for over
voltage and over current in addition to the resistors
(RVRef, RIRef1, and RIRef2) selected.
Figure 15. IDAC8 Configuration for OV-OC Circuit
The IDAC current is passed through resistances RVRef,
RIRef1, and RIRef2 to develop reference voltages.
These resistances must be chosen based on the following
equations:
RVref =
Vmax ∗ RVscale
I DAC _ VREF
(
)
Where
RVscale =
RVs 2
(RVs1 + RVs 2 )
RI Re f 1 =
RI Re f 2 =
I max ∗ Rs
(I DAC _ CREF )
I DAC _ VREF ∗ RV Re f
(I
DAC _ CREF
)
− RI Re f 1
In these equations, RVs1, RVs2, and RS are chosen based
on the requirements described in Battery Parameter
Measurement. Vmax and Imax are defined by the battery
chosen. For the sake of calculation, the current in the two
resistor paths are assumed first and the resistor values
are calculated based on these values. The IDAC_VREF is the
current through RVRef. The IDAC_CREF is the current through
the reference resistor string, and equal to difference of
total IDAC current and IDAC_VREF.
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PSoC® 3 and PSoC 5LP - Single-Cell Lithium-Ion (Li-ion) Battery Charger
Dithered PWM
Dithered PWM is the custom component included in the
project. This design gives high resolution by dithering the
duty cycle between two adjacent values. High resolution in
the PWM duty cycle is required in the switching method to
get a fine variation in current through the battery.
Figure 17 shows the design of the Dithered PWM
component. These internal components are included for
your reference and are placed automatically when the
Dithered PWM component is placed.
Timers
Two timers shown in Figure 18 are used in the project for
generation of timeouts and interrupts.
Timer_Scan: This 16-bit timer gives periodic interrupts to
the CPU to execute the charging state machine.
Timer_TimeOut: This sets the time limit during various
stages of battery charging. When a timeout interrupt
occurs, charging is stopped.
Figure 18. Timers for Battery Charger
Figure 17. Dithered PWM Design
The PWM component generates two PWM signals: pwm1
and pwm2. The pwm2 duty count is kept one more than
the pwm1 duty count. Out of the two PWMs, one is
selected at a time depending on the PrISM component
output. The PrISM component generates a pseudorandom sequence with configurable average duty cycle (or
pulse density). It receives a clock input from the terminal
count output of the PWM component. By varying the pulse
density of the PrISM component, a very fine variation in
duty cycle is obtained between two adjacent duty cycle
values of the PWM component.
With 8-bit PWM and the PrISM component, you can get a
resolution of 16 bits in the duty cycle. The most significant
8 bits of the 16-bit duty cycle value is loaded into the PWM
component and the lower significant 8 bits are loaded into
the PrISM component.
The Dithered PWM is required for the switching method of
implementation. You can use it for the linear method to
maintain the same project for the two methods, but a
standard Cypress library 16-bit PWM is also sufficient for
the linear method. Appendix E: Alternative Implementation
Options with Tradeoffs shows this option of
implementation. Other details on custom components can
be found in the PSoC Creator Component Author guide.
www.cypress.com
Calibration
During charging, a Li-ion battery requires accurate control
of voltage when it is at near full charge; < 0.75% error is
widely accepted. As the battery voltage is scaled down
using resistors, the scaling factor needs to be accurately
known. The error introduced by Delta-Sigma ADC is less
than 0.2% error across process, temperature, and supply
voltage variations. Therefore, ADC error is negligible. The
majority of error is introduced by the potential divider
resistor tolerances. Highly accurate resistors with
tolerance values as low as 0.01% are available but they
are costly. An alternative is to use a low-cost, hightolerance (1% or 5%) resistor and measure scaling factor
in the factory. During this factory calibration, a known
voltage can be given in place of the battery. The scaled
voltage read by the device divided by the known input
voltage is the scaling factor.
In this project, the calibration routine is written which can
be invoked by grounding Pin_Calibration (P1[7]).
Pin_Calibration is configured in pull-up mode. When the
PSoC device is reset, Pin_Calibration is polled to see if it
is grounded. If it is, it enters the calibration routine.
Otherwise, it takes the scale factor from a flash location.
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PSoC® 3 and PSoC 5LP - Single-Cell Lithium-Ion (Li-ion) Battery Charger
The flash location will be programmed initially with an
approximate value. When the device enters the calibration
routine, it assumes a known reference voltage is provided
at the battery terminals points. (In this project, 4.2 V is
assumed as the reference voltage.) After reading the
voltage, scaling factor is calculated and flash location is
updated.
A USB component was added to the project, and data
from the USB was plotted on a tool developed in C#. The
LCD component is also placed to display voltage, current,
temperature, and PWM duty cycle count. The additional
components required for development and not for
production are shown in Figure 20.
Figure 20. Components for Debug and Display
Test Setup and Results
A PCB was designed with the external components, for
the switching method battery charger, shown in Figure 2.
The board was designed to be an expansion board for
CY8CKIT-001, as shown in Figure 19. Appendix B gives
the Bill of Materials (BOM) and the schematic for this PCB
board. Gerber files for this board is also given provided.
Figure 19. Battery Charger EBK and CY8CKIT-001
USB Communication
A USB driver is required for USB communication. The INF
file is included with this application note. Appendix C: USB
Driver Installation explains the driver installation.
Charge Display Tool
You can plot the battery charging graphs using the tool
provided with this application note. The details of setting
up this tool are provided in Appendix D: Software Tool
Installation and Setup. An example plot of the charging
process is shown in Figure 21.
Figure 21. Charge Display Tool for Display and Debug
Conclusion
Li-ion battery charging can be done in multiple ways. The
firmware method of control and the linear and switching
method implementations are discussed in this application
note.
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Document No. 001-73468 Rev. *D
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PSoC® 3 and PSoC 5LP - Single-Cell Lithium-Ion (Li-ion) Battery Charger
Appendix A: Buck Circuit Component Selection
This section helps you select inductor value, output capacitor, and MOSFET.
The following assumptions are made:





Supply voltage Vin: 12 V
Full charge battery voltage: 4.2 V
Rapid charging current: 1 A
PWM switching frequency: 500 kHz
Inductor ripple current: 300 mA
The selection of the components for the buck regulator is as follows.
Inductor L Selection
Inductor voltage is given by:
L = (Vin - Vout)×
Duty
(Fsw× Iripple)
For this application, IRipple is assumed to be 30 mA with a charging current of 1 A. The duty cycle at Vout = 4.2 V (battery full
charge voltage) is around 0.35. The actual duty cycle will be a little larger to pump current in the battery. For a PWM frequency
of 500 kHz, this gives an inductor value close to 18 uH. A slightly larger value of inductance of 22 uH is chosen to keep a
margin of safety.
The current handling capability of the inductor should be greater than (load current + ripple current). Load current is the battery
charging current, which is 1 A maximum. Because the assumed ripple current is close to 300 mA, the inductor should be able
to handle minimum current of 1.3 A.
The following graph shows the ripple current for a given inductor value for the assumptions mentioned previously.
Output Capacitor C Selection
C=
(ripple current × Ton)
(ripple voltage - (ripple current × ESR))
A low ESR capacitor should be selected to have low ripples in the output voltage. The 30 mΩ ESR capacitor is selected for this
application. Duty is assumed to be 50% max; this gives Ton as 1 us. Capacitance of 22 uF gives the ripple voltage around
26 mV across the output. This ripple voltage drops across the internal resistance of the battery. Ripple current is taken as
350 mA for inductor value of 22 uH to keep a margin of safety.
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PSoC® 3 and PSoC 5LP - Single-Cell Lithium-Ion (Li-ion) Battery Charger
The following graph shows the variation in output voltage ripple for capacitance value for the assumptions mentioned
previously.
Dual MOSFET Selection
MOSFET selection is based on the load requirement, ripple current, and the supply voltage.
Drain current rating: Both the MOSFETs will handle load current + ripple current that gets bypassed through the output
capacitor. Therefore, the MOSFET continuous current rating should be greater than (1 A+0.35 A=1.35 A).
Drain-Source and Gate-Source voltage rating: This should be greater than the supply voltage.
FDC6561 dual MOSFET IC is selected, which has a 30 V drain-source voltage rating, a 20 V gate-source voltage rating, and a
continuous drain current rating of 2.5 A.
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Document No. 001-73468 Rev. *D
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PSoC® 3 and PSoC 5LP - Single-Cell Lithium-Ion (Li-ion) Battery Charger
Appendix B: Schematic and Bill of Materials for Switching Method of Current
Control
This section includes the schematic and the BOM for the EBK to test the battery charger functionality is provided. The main
board (CY8CKIT-001) has the PSoC and USB functionality, and the rest of the external circuitry is on this expansion board.
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Document No. 001-73468 Rev. *D
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PSoC® 3 and PSoC 5LP - Single-Cell Lithium-Ion (Li-ion) Battery Charger
Table 3. Bill of Materials (BOM)
Manufacturer
Manufacturer
Part Number
Reference
Quantity
Description
1
ON SEMICONDUCTOR
ADP3120AJRZ
U1
1
IC MOSFET DVR DUAL 12 V 8-SOIC
2
FAIRCHILD SEMICONDUCTOR (VA)
FDC6561AN
U2
1
MOSFET N-CHAN DUAL 30 V SSOT6
3
NXP SEMICONDUCTORS (VA)
PMEG3020EH,115
D1,D2,D3
3
SCHOTTKY RECT 30 V 2 A SOD123F
4
Generic
Generic
L1
1
INDUCTOR PWR UNSHIELD 22 UH SMD
5
Generic
Generic
BAT
1
HOLDER BATT 1/LI-ION PROTECTED
6
Generic
Generic
C4
1
CAP AL POLY CHIP 22UF 16V ESR 30 mΩ SMD
7
Generic
Generic
R9
1
2.2 kΩ 1% 0805
8
Generic
Generic
R4
1
330 kΩ 5% 0805
9
Generic
Generic
R6
1
2.2 kΩ 5% 0805
10
Generic
Generic
R5
1
0.2 Ω 1/4 W 1% 0805 SMD
11
Generic
Generic
R3
1
499 kΩ 5% 0805
12
Generic
Generic
R12
1
10 kΩ 5% 0805
13
Generic
Generic
R1,R2
2
10 Ω 1/4 W 5% 0805 SMD
14
Generic
Generic
R10
1
15 kΩ 1/4 W 1% 0805 SMD
15
Generic
Generic
R8
1
0.0 Ω 1/8W 0805 SMD
16
Generic
Generic
R7
1
15 kΩ 1% 0.125 W 0805
17
Generic
Generic
C1, C5
3
CAP CERM .01 UF 5% 16 V NP0 0805
18
Generic
Generic
C6
1
CAP CER 10 UF 16 V X5R 20% 0805
19
Generic
Generic
C3
1
CAP CER .47 UF 16 V X7R 0805
20
Generic
Generic
C8, C9
1
CAP .10 UF CERAMIC X7R 0805
22
Generic
Generic
H1
1
CONN HEADER R/A 40POS GOLD SMD
23
Generic
Generic
R11
1
THERMISTOR 10 kΩ NTC 0805 SMD
24
Generic
Generic
C2
1
CAP CER 0.1 UF 50 V X7R 0805
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Document No. 001-73468 Rev. *D
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PSoC® 3 and PSoC 5LP - Single-Cell Lithium-Ion (Li-ion) Battery Charger
Appendix C: USB Driver Installation
When the demo board is connected to the computer through a USB cable, the “Found New Hardware” message will appear,
as shown in the following figure.
Click Next on this screen and select Install from a list or specific location (Advanced). Click Next. The following screen
appears. Use the Browse field to find the INF file.
Click Next to complete and finish the installation.
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Document No. 001-73468 Rev. *D
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PSoC® 3 and PSoC 5LP - Single-Cell Lithium-Ion (Li-ion) Battery Charger
Appendix D: Software Tool Installation and Setup
Step 1: Click on the Setup file in the charge display tool folder provided with this application note.
Step 2: Follow the sets as guided by the tool for installation.
Step 3: Open the tool from Startup > Cypress Semiconductor > Charge display.
Step 4: Connect the COM associated with Li-ion battery charger.
Step 5: Enter the parameters of the ADC and the resistors chosen into the appropriate fields
Voltage Measurement
Differential Measurement: Select the box if the ADC is a differential ADC.
Clear the box if it is a single-ended ADC.
ADC resolution: Select the same resolution used for the ADC
ADC Range:
Select the same range used for the ADC
Voltage Divider: This is the hardware voltage scale used for the battery voltage attenuation.
=
RVsense 2
(RVsense1 + RVsense 2 )
Current Measurement
Differential Measurement: Select the box if the ADC is a differential ADC.
Clear the box if it is a single-ended ADC.
ADC resolution: Select the same resolution used for the ADC
ADC Range:
Select the same range used for the ADC
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Document No. 001-73468 Rev. *D
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PSoC® 3 and PSoC 5LP - Single-Cell Lithium-Ion (Li-ion) Battery Charger
Current Gain:
Choose the appropriate gain, if additional gain is added to current measurement
Sense Resistor: Enter the current sense resistor value RIsense
Temperature Measurement
Temp Scale: The thermistor component returns the temperature value scaled up by 100. For example, it returns 2345 when
the temperature is 23.45 °C. This value can be scaled down in firmware or passed onto the tool as it is and scaled in the tool.
Graph Parameter Setup
When you click Choose settings, the following form for the graph settings appears.
This can be used to change the voltage and current threshold levels displayed on the charge display tool, shown in the earlier
figure. All the parameters have to be matched to the parameters set in the battery charger project to make sure that the
thresholds line up.
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Document No. 001-73468 Rev. *D
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PSoC® 3 and PSoC 5LP - Single-Cell Lithium-Ion (Li-ion) Battery Charger
Appendix E: Alternative Implementation Options with Tradeoffs
This section shows the alternate implementation methods. The differences between the two methods are only to show
different options and tradeoffs during an implementation. You can choose any method that is suitable for your application.
Biasing Thermistor using IDAC
A second approach to measuring temperature with advantages of lower pin and memory usage is provided in this section. In
this method, an IDAC is used to source a known amount of current through the thermistor, and the voltage across it is
measured to obtain its resistance. The disadvantages are the accuracy will be lower, since the offset and gain errors are not
being accounted for, and the coefficients of the thermistor have to be provided by you in firmware.
Over Voltage and Over Current Protection
The method explained for the OV/OC in the earlier sections of this application note has the advantage of using one IDAC. Its
disadvantage is the complication introduced in calculating the external resistors. Some modifications of the circuit are given in
this section to show the options for tradeoffs.
Two IDACs are used instead of one to generate the reference voltages for OV and OC. This makes the resistor selection less
complicated for the user than the single IDAC method explained in switching method. The second option shown is to route the
signal from the IDAC to the comparator internally, instead of connecting the two pins externally. This option saves a pin, but
requires manual routing between the IDAC and the comparator. This is to make sure that the IDAC connection to the resistor
is made at the same location as the connection to the comparator. When automatic routing is used, additional switches are
used between the comparator connection and the pin, which causes the voltage seen at the comparator to be different from
the voltage at the pin and makes the fault detection erroneous.
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Document No. 001-73468 Rev. *D
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PSoC® 3 and PSoC 5LP - Single-Cell Lithium-Ion (Li-ion) Battery Charger
Battery Current Control with PWM
The charge current passed to the battery is decided based on the state of the battery. The dithered PWM was used in the
main section of the application note as the duty cycle required for the switching method is high. The dithered PWM can be
used for the linear method to maintain consistency in the project used. If you are interested in linear method alone, you can
use the standard PWM instead of the dithered PWM for linear method to save additional component and memory usage. The
connections for linear method with a regular PWM, instead of a custom Dithered PWM component, is shown in following
figure. A PWM-DAC is formed by using external RC low-pass filter. The voltage obtained at the output of the low-pass filter
controls the current through Q1 and thereby Q2. The current through Q2 is the charge current to the battery.
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Document No. 001-73468 Rev. *D
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PSoC® 3 and PSoC 5LP - Single-Cell Lithium-Ion (Li-ion) Battery Charger
Document History
®
Document Title: PSoC 3 and PSoC 5LP - Single-Cell Lithium-Ion (Li-ion) Battery Charger – AN73468
Document Number: 001-73468
Revision
ECN
Orig. of
Change
Submission
Date
Description of Change
**
3475721
RJVB
12/26/2011
New application note.
*A
3512389
RJVB
01/30/2012
Updated project files. No technical updates.
*B
3818140
SREH
11/20/2012
Updated to include PSoC 5LP. Project files updated. Update to Battery Protection
logic.
Updated Software Version as “PSoC® Creator™ 3.0 or Higher”.
*C
4227505
SREH
12/20/2013
Updated attached associated projects to Creator 3.0.
Updated in new template.
Completing Sunset Review.
Updated Software Version as “PSoC® Creator™ 3.3 or Higher”.
Updated attached associated projects to Creator 3.3 SP1.
Updated project to use standard component.
*D
5048763
SREH
03/01/2016
Updated the following diagrams:
Thermistor Calculator Component.
Battery Parameter Measurement.
Charge Display Tool for Display and Debug
Appendix D images.
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Document No. 001-73468 Rev. *D
22
PSoC® 3 and PSoC 5LP - Single-Cell Lithium-Ion (Li-ion) Battery Charger
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