AN55102 – PSoC® 1 Single Cell Li-Ion Battery Charger

AN55102 – PSoC® 1 Single Cell Li-Ion Battery Charger
AN55102
PSoC® 1 Single Cell Li-Ion Battery Charger with CY8C21x23
Author: Archana Yarlagadda
Associated Project: Yes
Associated Part Family: CY8C21x23, CY8C21x34
®
Software Version: PSoC Designer™ 5.4
Related Application Notes: AN2041
To get the latest version of
http://www.cypress.com/?rID=38367
this
application
note,
or
the
associated
project
file,
please
visit
®
AN55102 presents a Lithium-Ion (Li-Ion) battery charger design, with the smallest, low-cost PSoC 1 device –
CY8C21x23. This application note includes a dedicated PC-based software developed to perform real time charge
process monitoring and analysis.
Contents
1
2
3
4
5
6
1
Introduction ...............................................................1
PSoC Resources ......................................................2
2.1
PSoC Designer ................................................2
2.2
Code Examples ...............................................3
2.3
Technical Support ............................................4
Battery Charging Method ..........................................5
Temperature Control ................................................6
Charger Hardware ....................................................7
5.1
Low Side Current Sense ..................................8
5.2
Voltage Sense ............................................... 10
5.3
Temperature Measurement ........................... 10
5.4
Self Modulator Circuit .................................... 11
5.5
LED Control ................................................... 11
Charger Firmware................................................... 12
6.1
State Descriptions.......................................... 13
6.2
State Transition Descriptions ......................... 13
6.3
Current/Voltage Control ................................. 14
Production Calibration Procedure ........................... 16
PC Utilities and Debug Information ........................ 18
Design Enhancements ........................................... 20
9.1
Higher Charge Capacity Battery Charger ...... 20
10 Multicell Battery Charger ........................................ 21
10.1
Tiered Charge Profile..................................... 21
11 Appendix A: Charger Schematic for
8-pin CY8C21123 ................................................... 22
12 Appendix B: Charger Schematic for
16-pin CY8C21223 ................................................. 23
13 Appendix C: Charger BOM for
CY8C21123/CY8C21223 ....................................... 24
14 Appendix D: Firmware Flow Chart .......................... 25
Worldwide Sales and Design Support ............................. 28
7
8
9
Introduction
Li-Ion batteries have the greatest capacity to volume ratio and are found in notebooks, pocket PCs, cell phones, and
other cutting-edge consumer products.
This application note describes a single cell Li-Ion battery charger for a 500 mAh battery using the smallest and
lowest-cost chip in the PSoC family, CY8C21x23.The battery capacity and other battery parameters can easily be
changed by modifying corresponding constants in the firmware to support different batteries.
Multiple methods such as, self modulated voltage reference, pin multiplexing, time multiplexing of resources, and
code optimization have been used to implement the design in this chip. The charger can be embedded into consumer
and home appliances or industrial applications. The production level design can be implemented in an 8-pin
CY8C21123 device. The development can be done in CY8C21223 to add the digital communication required for
charge monitoring.
www.cypress.com
Document No. 001-55102 Rev. *E
1
PSoC® 1 Single Cell Li-Ion Battery Charger with CY8C21x23
2
PSoC Resources
Cypress provides a wealth of data at www.cypress.com to help you to select the right PSoC device for your design,
and quickly and effectively integrate the device into your design. In this document, PSoC refers to the PSoC 1 family
of devices. To learn more about PSoC 1, refer to the application note AN75320 - Getting Started with PSoC 1.
The following is an abbreviated list for PSoC 1:


Overview: PSoC Portfolio, PSoC Roadmap

Datasheets: Describe and provide electrical
specifications for the PSoC 1 device family.


2.1

Product Selectors: PSoC 1, PSoC 3,
PSoC 4, or PSoC 5LP. In addition, PSoC
Designer includes a device selection tool.
Application Notes and Code Examples:
Cover a broad range of topics, from basic to
advanced level. Many of the application
notes include code examples.
Technical Reference Manuals (TRM):
Provide detailed descriptions of the internal
architecture of the PSoC 1 devices.

Development Kits:

CY3215A-DK
In-Circuit
Emulation
Lite
Development Kit includes an in-circuit emulator
(ICE). While the ICE-Cube is primarily used to
debug PSoC 1 devices, it can also program PSoC
1 devices using ISSP.

CY3210-PSOCEVAL1 Kit enables you to evaluate
and experiment Cypress's PSoC 1 programmable
system-on-chip
design
methodology
and
architecture.

CY8CKIT-001 is a common development platform
for all PSoC family devices.
The MiniProg1 and MiniProg3 devices provide an
interface for flash programming.
PSoC Designer
PSoC Designer is a free Windows-based Integrated Design Environment (IDE). Develop your applications using a
library of pre-characterized analog and digital peripherals in a drag-and-drop design environment. Then, customize
your design leveraging the dynamically generated API libraries of code. Figure 1 shows PSoC Designer windows.
Note: This is not the default view.
1.
Global Resources – all device hardware settings.
2.
Parameters – the parameters of the currently selected User Modules.
3.
Pinout – information related to device pins.
4.
Chip-Level Editor – a diagram of the resources available on the selected chip.
5.
Datasheet – the datasheet for the currently selected UM
6.
User Modules – all available User Modules for the selected device.
7.
Device Resource Meter – device resource usage for the current project configuration.
8.
Workspace – a tree level diagram of files associated with the project.
9.
Output – output from project build and debug operations.
®
Note: For detailed information on PSoC Designer, go to PSoC
Designer Specific Documents > IDE User Guide.
www.cypress.com
Document No. 001-55102 Rev. *E
Designer > Help > Documentation >
2
PSoC® 1 Single Cell Li-Ion Battery Charger with CY8C21x23
Figure 1. PSoC Designer Layout
2.2
Code Examples
The following webpage lists the PSoC Designer based Code Examples. These Code Examples can speed up your
design process by starting you off with a complete design, instead of a blank page and also show how PSoC
Designer User modules can be used for various applications.
http://www.cypress.com/go/PSoC1Code Examples
To access the Code Examples integrated with PSoC Designer, follow the path Start Page > Design Catalog >
Launch Example Browser as shown in Figure 2.
Figure 2. Code Examples in PSoC Designer
www.cypress.com
Document No. 001-55102 Rev. *E
3
PSoC® 1 Single Cell Li-Ion Battery Charger with CY8C21x23
In the Example Projects Browser shown in Figure 3, you have the following options.




Keyword search to filter the projects.

Create a new project (and a new workspace if needed) based on the selection. This can speed up your design
process by starting you off with a complete, basic design. You can then adapt that design to your application.
Listing the projects based on Category.
Review the datasheet for the selection (on the Description tab).
Review the code example for the selection. You can copy and paste code from this window to your project, which
can help speed up code development, or
Figure 3. Code Example Projects, with Sample Codes
2.3
Technical Support
If you have any questions, our technical support team is happy to assist you. You can create a support request on the
Cypress Technical Support page.
You can also use the following support resources if you need quick assistance.


Self-help
Local Sales Office Locations
www.cypress.com
Document No. 001-55102 Rev. *E
4
PSoC® 1 Single Cell Li-Ion Battery Charger with CY8C21x23
3
Battery Charging Method
Lithium based batteries use a two-stage charge profile: activation and rapid charge stages. If the battery voltage is
less than 3.0 V, it means the cell is completely discharged and the battery must be activated. In the activation stage,
the battery is charged with a small constant current (typically 0.05 to 0.015 CA, where CA is the nominal battery
capacity) until the battery voltage reaches the desired level. The battery activation time is limited to approximately 1.5
to 3 hours, depending on battery manufacturer recommendations. If, during activation time, the battery voltage does
not rise above 3.0 V, the battery cell is considered damaged.
The rapid charge stage starts after the activation stage. Rapid charge consists of two modes: constant voltage and
constant current.
When the battery voltage is less than a specified level (typically 4.2 V, but depends on battery manufacturer
specifications), the charge is executed with the constant current (about 0.5 to 1 CA, depending on the battery
manufacturer recommendations). When the battery voltage reaches the specified level, the charge source switches to
the constant voltage mode (4.2 V). If the charge current drops below a specified limit, the charge process terminates;
the battery manufacturer recommends the users to set the rapid termination current to 0.07 to 0.2 CA.
The rapid charge stage must be protected by a timeout. The constant current time is estimated to provide 100% to
120% of the battery charge because during this mode the battery is charged up to 70% to 80%. The constant voltage
charge time is limited to approximately two hours, according to the manufacturer recommendations.
Figure 4 depicts the Li+ battery charge profile. Table 1 contains descriptions of the charge profile parameters and
default values used in this design.
Note that Li+ batteries are very sensitive to the charge voltage, current, and discharge limit. Therefore, they are
assembled with a built-in thermistor and protective circuit. This circuit protects the battery from over-charge and overdischarge, and limits the load and charge current to safe values. Without this circuit, the battery can explode under
adverse conditions. The charge source voltage limit accuracy must be better than 1%.
Figure 4. Li+ Battery Charging Profile
VMAX
8
7
VFULL
VBATT
VRE-CH
9
6
VRS
IMAX
4
IRAP
2
VACT
IACT
ITERM
ICHARGE
5
1
3
13
tSTART
14
tACT 10
www.cypress.com
tRAP
11
Document No. 001-55102 Rev. *E
tTERM
tVCONST 12
5
PSoC® 1 Single Cell Li-Ion Battery Charger with CY8C21x23
Table 1. Example of Charge Profile Parameters and Values
Marker
Parameter
Description
Value
Charging Parameters
1
IACT
Activation charge current
80 mA ± 30 mA
2
IRAP
Rapid charge current
500 mA ± 40 mA
3
ITERM
Termination current (use average of ICH over 1 second)
60 mA ±15 mA
4
IMAX
Emergency charge stop current
600 mA ± 60 mA
5
VACT
Activation charge start voltage
2.0 V ± 0.1 V
6
VRS
Rapid charge start voltage
3.0 V ± 0.1 V
7
VFULL
Full charge voltage
4.2V ± 0.03 V
8
VMAX
Emergency charge stop voltage
4.35 V ± 0.1 V
9
VRE-CH
Recharge voltage
4.0 V ± 0.1 V
Timing Requirements
10
tACT
Time limit for battery activation period
140 min
11
tRAP
Time limit for constant current rapid charge period
80 min
12
tVCONST
Time limit for constant voltage charge period
120 min
13
tSTART
Maximum time for battery activation (while VBATT < VACT)
20 sec
14
tTERM
Minimum time for charge complete (when ICHARG ≤ ITERM)
10 sec
Additional Parameters
4
15
IMIN
Minimum current for battery health test
25 mA
16
VDC_Vdd
Charger power supply voltage
5.2 V ± 0.2 V
Temperature Control
The charge process can be activated only if the battery temperature is within a specified limit. Typical temperature
values are 0 °C to +50 °C.
Figure 5 depicts the temperature profile. Table 2 contains descriptions of the temperature profile parameters and
default values used in this design.
Thermistor resistance is also used to check for the battery presence. The battery is considered disconnected when
the measured thermistor resistance is greater than ROPEN. This means there is no thermistor; therefore, no battery
pack is connected. A tiered current profile, with lower current at higher temperature can be supported with
modifications to the software. More information is provided in the Design Enhancements section of this application
note.
www.cypress.com
Document No. 001-55102 Rev. *E
6
PSoC® 1 Single Cell Li-Ion Battery Charger with CY8C21x23
Figure 5. Temperature Profile
ROPEN
5
THOT_STOP
3
THOT_RESTART
4
No charging
TBATT
2
TCOLD_RESTART
TCOLD_STOP
1
Charge in
process
Charge in
process
Table 2. Temperature Related Parameters
Marker
5
Parameter
Description
Value
1
TCOLD_STOP
Stop temperature measured from battery thermistor
0 °C
2
TCOLD_RESTART
Restart temperature measured from battery thermistor
TCOLD_STOP + 1 °C
3
THOT_STOP
Stop temperature measured from battery thermistor
50 °C
4
THOT_RESTART
Restart temperature measured from battery thermistor
THOT_STOP – 2 °C
5
ROPEN
Thermistor resistance limit for determining open circuit
40 kΩ (-7 °C)
Charger Hardware
Figure 6 shows the general structure of the charger. The following abbreviations are used within the PSoC block.

RS_TX: EIA-232 (RS-232) transmitter for debug purposes (uses external transceiver). It reports temperature,
voltage, and current to a PC. RS_TX is used only in the debug stage and may be removed in the released
product.




CPU: Central processor core for implementing charge algorithms and performing charge control functions.
PWM: Pulse-width modulator for driving the regulator.
ADC: Single Slope analog-to-digital converter for digitizing the analog signals.
AMUX: Analog multiplexers.
The signal from the PWM goes to a low-pass RC-filter (R8 and C1). The output of the RC filter is a constant voltage
signal proportional to the PWM duty cycle value. This output is connected to the base of the Q1 transistor. Therefore,
the PWM with an RC-filter is a PWM-DAC. The NPN transistor Q1 is driven by an analog signal from the PWM DAC
and regulates the battery charge current. The PWM period is set to 255 for accuracy, and can easily be adjusted in
the firmware. The combination of Q2 and Q1 avoid reverse current, which can discharge the battery when it is still
connected and the charger is turned off from the supply voltage. There is a 0.25 Ω resistor used as the current
sensor. Other resistors form the battery interface to allow transformation of the battery current, voltage, and
temperature into the signals that have a suitable voltage range for the PSoC analog inputs.
www.cypress.com
Document No. 001-55102 Rev. *E
7
PSoC® 1 Single Cell Li-Ion Battery Charger with CY8C21x23
Figure 6. Charger Structure
Q2
Supply Vdd
SERIAL_TX
Current/Voltage
Control
RS_TX
( debug
only)
CPU
R5
Q1
PWM
R8
Li- ion battery pack
C1
R20
Charge+
Vref
CMP
R2
Vbg
1.3V
T sense
Temperature
Sense
C2
R1
T
R3
ADC
Charge and
PSoC GND
Voltage
Sense
AMUX
R2
R4
R9
D1
PSoC internals
Charge and
PSoC GND
R10
Current
Sense
LED
Control
Charge and
PSoC GND
R 11 to R14
Supply GND
To correctly implement charge algorithms, the following must be measured accurately: charge current, battery
voltage, and temperature. As the voltage drops on the corresponding resistors, all parameters are measured using
the ADC.
To limit current flow from the battery through the interface resistors for current and voltage measurement, precision
resistor dividers with large resistor values are used.
5.1
Low Side Current Sense
The current measurement is on the low side as shown in Figure 7, where the current flowing out of the negative
terminal of battery (Node N1 to Node N2) is measured.
Figure 7. Current Sense Circuit
Vref
N4
Li-ion battery pack
R9
iSense
N3
R10
T
iCharge
Supply GND
N2
N1
R11 to R14
www.cypress.com
Document No. 001-55102 Rev. *E
Battery and
PSoC GND
8
PSoC® 1 Single Cell Li-Ion Battery Charger with CY8C21x23
The current shunt resistor is outside the PSoC supply voltage to maximize and keep constant voltage range for the
ADC in the PSoC. This avoids the ground being at a different potential depending on the current flow into the battery.
The voltage value to be measured at Node N2 is negative with respect to PSoC, which has the ground at Node N1.
Thus, a reference voltage and a summing node are required to pull this to a positive value. The reference voltage is
generated using the self modulator circuit described later in this document. The advantage of this approach is that the
voltage is pulled to a range higher than the offset of the ADC and thus the error due to offset can be compensated.
Precise accuracy of current measurement is necessary, when near the 4.2 V battery voltage. Therefore, during the
general calibration procedure, when the transistor Q1 is off, measure the voltage bias on the current sense resistor
and store it in nonvolatile memory. Subtract this memorized bias voltage from each measurement value during the
normal charge process. The following equation depicts this measuring scheme:
n
ni  VCh arg e  ADC max
 V ADC max

  nbias

n
nbias  Vref  bias  ADC max
 V ADC max



VCh arg e  I Ch arg e  i
Equation 1
Equation 2
Equation 3
Where,
nbias is the ADC code when ICharge is zero
∆ni is the ADC code after removing the bias voltage and ADC offset voltage
nADCmax is full scale ADC code and the value is equal to 1023 for a 10-bit single slope ADC
VADCmax is full scale ADC voltage for the full scale ADC code
ICharge is battery charge current
Vref is self modulated reference voltage (1.3 V)
 bias
is the resistive divider coefficient for Vref. (equal to 0.25 when R10 = 100 kΩ and R9 = 300 kΩ)

R

10

 bias  
R

 10 R9 
i
Equation 4
is the coefficient to convert the current iCharge into voltage iSense (equal to 0.1875 when R10 = 100 kΩ, R9 =
300 kΩ, and R11 = 0.25 Ω)

R9 

R

R
9 
 10
 i  R11 
www.cypress.com
Equation 5
Document No. 001-55102 Rev. *E
9
PSoC® 1 Single Cell Li-Ion Battery Charger with CY8C21x23
5.2
Voltage Sense
The battery voltage is scaled down to the range of the ADC10 by using the resistor divider R3 and R4 shown in
Figure 8.
Li-ionCircuit
battery pack
Figure 8. Voltage Sense
VBatt
R3
VSense
T
R4
Battery and
PSoC GND
The scaling is such that 4.2 V, which is the most accurate measurement required, corresponds to the 1.3 V to which
the ADC10 is calibrated. The VSense voltage signal is measured by the Single Slope ADC (ADC10).
n
nV  VBatt V  ADC max
 VADC max



Equation 6
Where,
VBatt is battery voltage.
βV is the resistive divider coefficient (equal to 0.306 for R3 = 22.6 kΩ and R4=10 kΩ):

R

4

V  
R

 4 R3 
Equation 7
To obtain accurate voltage measurements, a calibration technique is used. The PSoC’s bandgap reference voltage
error and ADC gain causes a non-calibrated voltage measurement error. The calibration procedure with external
voltage reference compensates for all gain errors.
The single slope ADC is calibrated by modifying the capacitor value to obtain the expected counts for a bandgap
voltage measurement, and this value is stored in flash. This value is used for every measurement cycle to calibrate
the ADC to compensate for any gain errors or temperature variations. The complete details of calibration are given in
a following section of this document.
5.3
Temperature Measurement
Temperature measurement is implemented with resistor R1 and the thermistor in the battery, as shown in Figure 9.
The voltage VT across the thermistor is measured with the ADC, using equations 8 and 9. The reference bias voltage
Vref is obtained with a self modulator circuit that is described later.
www.cypress.com
Document No. 001-55102 Rev. *E
10
PSoC® 1 Single Cell Li-Ion Battery Charger with CY8C21x23
Figure 9. Temperature Measurement
Li-ion battery pack
VBatt
Vref
R1
T
VT
Battery and
PSoC GND
n
nT  Vref T  ADC max
 VADC max

R



Equation 8

therm

T  
R
 therm  R1 
Equation 9
The thermistor transfer function is nonlinear, but there is no need to obtain the temperature value in linear units for
this design. Therefore, only the temperature thresholds during the charge must be checked. This is done by analyzing
the ADC code (nT). Hysteresis is added for the lower and upper bounds of the in/out temperature range to prevent
multiple triggers when the temperature is close to the preset range (see Figure 5).
5.4
Self Modulator Circuit
The CY8C21x23 PSoC device does not have any analog output pins and can provide no native analog reference
voltage. The self modulator circuit is formed with the comparator block and an external RC low-pass filter as shown in
Figure 10.
The feedback causes the comparator output to turn ON and OFF with a duty cycle. The average voltage after the
low-pass filter is equal to Vbg. This technique has a pending patent and it should be used only with Cypress products.
5.5
LED Control
An LED is used to indicate charger state. Because the project uses a small package with low pin count, the
temperature sense and LED control are multiplexed. The drive mode of the pin is set to “HI-Z, Analog” when the
temperature measurement is performed and to “Strong” high when the LED function is ON. All possible states
displayed by the LED are described in Table 3.
Table 3. LED States
No.
Charger State
Led State
1
Charge (Activate, Rapid States)
ON
2
Charge Complete, No Battery States
OFF
3
Temperature Over Range, Battery Error
BLINKING
www.cypress.com
Document No. 001-55102 Rev. *E
11
PSoC® 1 Single Cell Li-Ion Battery Charger with CY8C21x23
6
Charger Firmware
The charger firmware consists of two parts: one is the main charging functionality and the other is intended to
calibrate the charger in the factory.
The main part of the firmware is built as a state machine. A diagram of the various states of the state machine is
shown in Figure 11.
The order of connecting and disconnecting the three battery terminals is random. The physical ordering of the signals
on the connector can vary from design to design. Therefore, all the possible sequences of Battery+, Battery-, and
Thermistor connections and disconnections are allowed when a battery is installed or removed. There is no ordering
that results in a lockup condition, or result in false error detection.
Figure 10. Self Modulator Circuit
PSoC
P1[1]
Vbg
Comparator
Bus
_
P0[0]
Voltage
Reference
Global Bus
+
Figure 11. Charger State Diagram
reset
d
No Battery
l
Initialization
f
Charge
Complete
k
e
g
a
j
Battery
Error
i
Activation
j
h
b
c
Wait For
Temperature
j
Rapid
Charge
www.cypress.com
Document No. 001-55102 Rev. *E
12
PSoC® 1 Single Cell Li-Ion Battery Charger with CY8C21x23
6.1
State Descriptions
No Battery: LED = OFF, no charge. Waits for the battery to be connected.
Initialization: LED = ON. Determines the battery presence and its state. If thermistor is present but the battery
voltage value is below VACT, a short time battery initialization by IACT current is used.
Activation: LED = ON. Charge by constant IACT current until voltage reaches VRS.
Rapid Charge: LED = ON. Constant current mode at IRAP until voltage reaches VFULL. Then changes to constant
voltage until current falls below ITERM.
Charge Complete: LED = OFF, done charging. Wait for the battery to be removed, or for voltage to drop below V RECH to restart charge.
Battery Error: LED = BLINK and turn off charge. Error condition. Wait for the battery to be removed, or power cycled.
Wait For Temperature: LED = BLINK, stop charging. Temperature is outside of the desired range limits. Wait for the
temperature to return within the limits. Then move to the Initialization state.
6.2
State Transition Descriptions
a)
IF VACT < VBATT ≤ VRE-CH
THEN Activation Current
If the battery is detected and the battery is not already charged, then turn the LED on and transition to Activation.
b)
IF VRS ≤ VBATT < VMAX
THEN Rapid Charge
If the battery voltage rises above the Rapid Charge start voltage, then transition to Rapid Charge.
c)
IF VFULL ≤ VBATT < VMAX
AND ICHARGE ≤ ITERM
for tTERM seconds
THEN Charge Complete
If charge current falls below ITERM for tTERM seconds after the battery voltage has reached V FULL, turn off charge
current and turn off status LED and transition to Charge Complete.
d)
IF RTHERMISTOR ≥ ROPEN
THEN Wait for Battery
If a battery is disconnected, then transition to No Battery.
e)
IF VBATT ≤ VRE-CH
THEN Initialize the Charging Process
If the battery voltage falls below the re-charge voltage, then transition to Initialization.
f)
IF VRE-CH < VBATT
THEN Charge Complete
If the battery is detected and is fully charged then turn off the LED and transition to Charge Complete.
g)
IF VBAT < VACT for tACT seconds
THEN Battery Error
If the battery voltage is less than VACT after tSTART seconds of activation current, then turn off charge current,
BLINK LED, and transition to Battery Error.
h)
IF VBATT ≥ VMAX
OR ICHARGE ≥ IMAX
OR Constant Current Charge Duration > tRAP
www.cypress.com
Document No. 001-55102 Rev. *E
13
PSoC® 1 Single Cell Li-Ion Battery Charger with CY8C21x23
OR Constant Voltage Charge Duration > tVCONST
THEN Battery Error
When the battery voltage exceeds VMAX, turn off charge current, BLINK LED, and transition to Battery Error.
If the charge current is greater than IMAX, turn off charge current, BLINK LED, and transition to Battery Error.
If the constant current charge time is longer than t RAP, or the constant voltage charge mode lasts longer than
tVCONST seconds, then turn off charge current, BLINK LED, and transition to Battery Error.
i)
IF VBATT ≥ VMAX
OR ICHARGE ≥ IMAX
OR after tACT seconds: VBATT < VRS
THEN Battery Error
When battery voltage exceeds VMAX, turn off charge current, BLINK LED, and transition to Battery Error.
If charge current is greater than IMAX, turn off charge current, BLINK LED, and transition to Battery Error.
If the activation mode lasts longer than t ACT seconds, then turn off the charge current, BLINK LED, and transition
to Battery Error.
When battery voltage exceeds VMAX and charge current is less than IMIN (indicating battery lead path is broken),
then BLINK LED and transition to Battery Error.
j)
IF TBATT ≤ TCOLD_STOP
OR TBATT ≥ THOT_STOP
THEN Temperature Outrange
When temperature reading from thermistor is out of range, turn off charge current, turn LED OFF, and transition
to Wait For Temperature.
k)
IF TBATT > TCOLD_RESTART
AND TBATT < THOT_RESTART
THEN Resume Charging
When temperature reading returns to operation range, restart charge in Initialization.
l)
IF RTHERMISTOR < ROPEN
THEN Initialize the Charging Process
If a battery is detected, then transition to Initialization.
6.3
Current/Voltage Control
To build a Li+ battery charger, the regulator must be capable of regulating both charge current and voltage. This
charger employs a simple adaptive regulator. The regulator operation is based on increasing the PWM duty cycle if
the charge voltage or charge current is smaller than the desired value. If the charge voltage or current are greater
than the desired value, the PWM duty cycle is decreased. The circuit for the current control is shown in Figure 12.
The PWM output is converted into a DC voltage value by using the RC low-pass filter (LPF). This voltage, when
greater than the threshold voltage of transistor Q1, along with the resistor R20, determines the current in Q1
transistor. This in turn controls the current in Q2 transistor and thereby the current into the battery.
www.cypress.com
Document No. 001-55102 Rev. *E
14
PSoC® 1 Single Cell Li-Ion Battery Charger with CY8C21x23
Figure 12. Regulation Circuit
Li-ion battery pack
Q2
Supply
Vdd
T
R5
Battery and
PSoC GND
PWM
output
Q1
R8
C1
R20
The PNP transistor Q2 also acts as a diode, preventing the battery from discharging when no power is applied to the
charger. Figure 13 illustrates the regulator operation.
Figure 13. Charger Regulator Operation
VBATT
VBATT<VFULL
+STEP
ICHARGE
IREG
VBATT
ICHARGE<IREG
AND
PWM
pulsewidth
0..PWMmax
PWMDAC
VBATT>VFULL
-STEP
ICHARGE
IREG
ICHARGE>IREG
OR
To obtain faster current regulation, a scheme with an adaptive step regulator is used (see Figure 14). If the regulator
current is greater than the charge current by the Imis1 predefined value, the regulator step is set equal to STEP1.
Current differences of Imis2 and Imis3 correspond to STEP2 and STEP3, respectively. If the difference between the
target charge current and the measured current is minimum (Imis3), then the PWM step is set to ‘1’. With current
difference of ImisOver, STEP_OVER is used for a fast reaction to minimize current overflow. When the battery
voltage rises above 4.2 V and the FConstVoltage flag is set, the regulator step is set to ‘1’ and there is no change to
the step size during the constant voltage charge period.
www.cypress.com
Document No. 001-55102 Rev. *E
15
PSoC® 1 Single Cell Li-Ion Battery Charger with CY8C21x23
Figure 14. Adaptive Step Charge Regulator
Step = STEP_OVER
Ireg
Imis3
Imis2
Imis1
ImisOver Step = 1
Step = 1
Step = STEP3
Step = STEP2
Ich
Step = STEP1
7
Production Calibration Procedure
As previously mentioned, all devices must be calibrated during the manufacturing process. Calibration is an easy
procedure but needs a precise 4.20 V source, instead of a battery, connected to the charger connector. It also needs
P1[1] (pin 4 of the ISSP connector) connected to ground as shown in Figure 15. After start, the charger is used to
check the P1[1] pin. If P1[1] is externally pulled down, then the charger goes to calibration mode. P1[1] is connected
to pin 4 of the ISSP connector and the PSoC ground is connected to pin 2 of ISSP connector (J2, see schematic in
Appendix A: Charger Schematic for 8-pin CY8C21123). In this mode, transistors Q1 and Q2 are off, and the charger
measures the constant 4.20 V. The voltage sense resistors (R3 and R4) are chosen such that 4.2 V is scaled down to
1.3 V.
Figure 15. Setup for Calibration
Vdd
1
2
Power
connector
1
2
3
4
5
ISSP/Debug
Connector
+
Battery
Precision
Connector T
4.20 V source
-
Charger
The Single Slope ADC (ADC10) is calibrated with the internal bandgap voltage, which is nominally 1.3 V. Thus,
scaling down 4.20 V to 1.3 V ensures accurate reading at that point. The calibration of the single slope ADC is shown
in Figure 16.
www.cypress.com
Document No. 001-55102 Rev. *E
16
PSoC® 1 Single Cell Li-Ion Battery Charger with CY8C21x23
Figure 16. Block Diagram of Single Slope ADC
Vdd
RAMP
Generator
ENABLE
ADC
Vin
Comparator
Counter
CAPVAL
PWM
The current into the CAPVAL is started at the start of an ADC conversion and a voltage ramp is generated. The
comparator trips when the ramp voltage value reaches the input voltage. The Counter counts the time from the start
of the current to the trip of the comparator. The PWM controls the ON and OFF times of the conversion. During PWM
ON, the voltage ramp is on and the Counter counts. During PWM OFF, the capacitor is discharged and the answer is
processed. The calibration function (ADCCAL) adjusts the value of CAPVAL and hence the slope of voltage ramp for
full scale
The calibration function (ADCCAL) of the ADC changes the CAPVAL capacitor value to obtain the desired ADC
counts for the internal bandgap voltage. The firmware is setup to do the following:
Step 1: An initial ADC counts value, as shown in Equation 10, is assigned to
n
niCAL  Vbandgap ADC max
 VADC max



niCAL .
Equation 10
Step 2: ADC10 is calibrated with the ADCCAL function with
niCAL
as the counts for bandgap voltage.
nV (Vsense = 4.20 V).
Step 4: niCAL is increased if nV > niCAL or decreased if nV < niCAL .
Step 5: Step 2 to Step 4 is repeated till nV == niCAL
Step 6: niCAL is stored in flash and used as the ADC calibration point for every measurement cycle.
Step 3: Vsense is measured,
Step 7: The calibration function remains in an infinite NOP loop until a reset occurs.
www.cypress.com
Document No. 001-55102 Rev. *E
17
PSoC® 1 Single Cell Li-Ion Battery Charger with CY8C21x23
8
PC Utilities and Debug Information
The charger control software monitors the charge process. The program interface is simple (Figure 17). Set the
COM#, press the Start button, and then turn on the charger. The software then presents the charger state and
displays graphs with charge current and voltage (see Figure 17). The default values for the software must be
changed to match the profile required by clicking on the “Settings”. For the project accompanying this application note
(500 mAh battery charger), the settings are shown in Figure 18.
Figure 17. PC Charger Monitoring Software
www.cypress.com
Document No. 001-55102 Rev. *E
18
PSoC® 1 Single Cell Li-Ion Battery Charger with CY8C21x23
Figure 18. Settings Window for the Associated Project
The charger can send two kinds of packets to the PC utility. Both packets are in text format and all values are
hexadecimal. The first packet is an initialization packet that is sent once, after the charger is powered on. This
package has a length of 22 bytes and contains the stored nonvolatile memory voltage thresholds that are set in the
code. Packet details are represented in Table 4. The packet’s structure is shown in Figure 19.
Table 4. Initialization Package
No.
Length in Bytes
Reference
Description
1
1
I
Character ‘I’ as start marker of initialization packet
2
4
VFULL
4-digit hexadecimal value of full-charge voltage (ADC code)
3
4
VACT
4-digit hexadecimal value of activation start voltage (ADC code)
4
4
VRS
4-digit hexadecimal value of rapid start voltage (ADC code)
5
4
VMAX
4-digit hexadecimal value of emergency stop voltage (ADC code)
6
4
VRE_CH
4-digit hexadecimal value of re-charge start voltage (ADC code)
7
1
CR
Character with ASCII code 13 (CR) as marker of end of packet
Figure 19. Initialization Package Structure
0
‘I’
1
4
VFULL
5
8
VACT
9
12
VRS
13
16
VMAX
17
20
VRE-CH
21
CR
The second packet is sent regularly and contains the current state of the charger battery voltage, charger current,
temperature values, and errors. Using this packet, the PC utility builds charts and displays actual battery parameters.
This packet has a length of 16 bytes. Packet details are represented in Table 5. The packet’s structure is shown in
Figure 20.
www.cypress.com
Document No. 001-55102 Rev. *E
19
PSoC® 1 Single Cell Li-Ion Battery Charger with CY8C21x23
The program in the PSoC does not calculate the actual current and voltage in amperes and volts. It only looks at ADC
counts and makes state machine decisions based on them. The PC utility calculates the amperes and volts for
debugging purposes.
Table 5. Information Packet
Description
No.
Length in Bytes
1
1
Character with ASCII code 10 (LF) as packet start marker
1
Charger State
0 – Initialization
1 – Battery Activation
2 – Rapid Charge
3 – Charge Complete
4 – Error
5 – Temperature Outrange
6 – No Battery Charger
3
1
Errors
0 – No Error
1 – Voltage Error (VBAT ≥ VMAX)
2 – Current Error (ICH ≥ IMAX)
3 – Activation Timeout
4 – Constant Current Rapid Charge Stage Timeout
5 – Constant Voltage Rapid Charge Stage Timeout
6 – Battery Initialization Timeout
4
4
4-digit hexadecimal value of charge current (ICHARGE) ADC code
5
4
4-digit hexadecimal value of battery voltage (VBATT) ADC code
6
4
4-digit hexadecimal value of voltage drop on thermistor used for temperature control
7
1
Character with ASCII code 13 (CR) as marker of end of packet
2
Figure 20. Information Package Structure
0
LF
9
1
2
State Error
3
6
ICHARGE
7
10
VBATT
11
14
T
15
CR
Design Enhancements
The project accompanying this application note is for designs with no voltage feedback regulation. The current into
the battery is thus limited by the power dissipation in transistor Q2. The charger in this application note is designed to
support batteries with a capacity up to 500 mAh.
9.1
Higher Charge Capacity Battery Charger
To charge batteries of higher capacity the options are: use an expensive PNP transistor with a higher power rating or
incorporate a feedback mechanism to decrease the voltage drop across current control PNP transistor (Q2) as shown
in Figure 21. In a complete system, the feedback control can be a fly-back circuit, which does the voltage regulation.
www.cypress.com
Document No. 001-55102 Rev. *E
20
PSoC® 1 Single Cell Li-Ion Battery Charger with CY8C21x23
Figure 21. Block Diagram for Higher Current Capacity Battery Charger
Voltage
Regulator
Current
Control
Li-ion battery pack
DC Supply
Voltage Sense
Vdd Control
(Zener)
PSoC
Temp Sense
T
RS_TX
(UART for
Debug)
10
Current Sense
LED
Multicell Battery Charger
To implement a multicell battery charger, the Vdd to PSoC must be regulated for the entire range of voltages (all
batteries discharged to fully charged). The voltage regulation across current control PNP transistor (Q2) is required to
facilitate higher current flow.
Figure 22. Block Diagram for Multicell Battery Charger
Voltage
Regulator
Current
Control
Li-ion battery pack
DC
Supply
Voltage Sense
Vdd
Regulation
PSoC
Temp Sense
T
RS_TX
(UART for
Debug)
10.1
Current Sense
LED
Tiered Charge Profile
This is straight forward to implement with the current project. The state machine can be easily modified to get a
different charge profile. A tiered rapid charge mode could be created that is dependent on the temperature by
modifying the state machine. Since the different states are well defined in the firmware, it is easy to add or modify a
few conditional statements to change the profile.
About the Author
Name:
Archana Yarlagadda
Title:
Application Engineer
Background:
Applications Engineer in Cypress with focus on PSoC applications. Masters in Analog VLSI from
University of Tennessee, Knoxville
www.cypress.com
Document No. 001-55102 Rev. *E
21
PSoC® 1 Single Cell Li-Ion Battery Charger with CY8C21x23
11
Appendix A: Charger Schematic for 8-pin CY8C21123
www.cypress.com
Document No. 001-55102 Rev. *E
22
PSoC® 1 Single Cell Li-Ion Battery Charger with CY8C21x23
12
Appendix B: Charger Schematic for 16-pin CY8C21223
www.cypress.com
Document No. 001-55102 Rev. *E
23
PSoC® 1 Single Cell Li-Ion Battery Charger with CY8C21x23
13
Appendix C: Charger BOM for CY8C21123/CY8C21223
Designator
C1, C2, C3, C4,
C5, C6
Value
0.1 uF
Digikey PN
Description
Quantity
PCC1762CT-ND
Capacitor 0.1 uF X7R 0603
6
D1
67-1552-1-ND
LED
1
DZ1
MMBZ5226B-FDICT-ND
Zener Diode
1
J2
WM4203-ND
ISSP Connector 5 pin 100 mil partially shrouded
1
2 pin header
1
J1
Q1
MMBT5089LT1GOSCT-ND
BJT - NPN
1
Q2
568-4167-1-ND
BJT – PNP
1
R1, R4
10K
P10.0KHCT-ND
Resistor 10K 1% 0603
2
R2
1K
P1.00KHCT-ND
Resistor 1K 1% 0603
1
R3
22K6
P22.6KHCT-ND
Resistor 22K6 1% 0603
1
R5
100 Ohms
P100HCT-ND
Resistor 100 Ohms 1% 0603
1
R6
39 Ohms
P39.0HCT-ND
Resistor 39 Ohms 1% 0603
1
R7, R8
3K9
P3.90KHCT-ND
Resistor 3K9 1% 0603
2
R9
100K
P100KHCT-ND
Resistor 100K 1% 0603
1
R10
300K
P300KHCT-ND
Resistor 300K 1% 0603
1
R11, R12, R13,
R14
1 Ohms
P1.0DCT-ND
Resistor 1 Ohms 1/8 Watt 0805 1%
4
www.cypress.com
Document No. 001-55102 Rev. *E
24
PSoC® 1 Single Cell Li-Ion Battery Charger with CY8C21x23
14
Appendix D: Firmware Flow Chart
Start
Init device
Check for
Connected
Callibrator
Yes
Perform Charger
calibration and
store coeficients
Permanent loop
Set
INITIALIZATION
state
Measure Vb, Ich, Tb
Calculate Avrg(Ich)
Send Debug Data
Check for
battery absent
Yes
(Rterm )
Set
NO_BATTERY
state
No
State
NO_BATTERY
Yes
Charge Off
Check for
battery present
Yes
(Rterm )
Set
INITIALIZATION
state
Start tSTART,
No
No
State
Yes
Init variables
INITIALIZATION
Check battery
temperature
Yes
Set WAIT FOR
TEMPERATURE
state
Yes
Set ERROR state
and error code
No
No
Check
timeouts
No
Check Vb≤VACT
Yes
Charge On
Set Ireg=IACT;
Regulate
No
Check Vb
≤VRE-CH
Yes
No
Yes
Set Ireg=IACT;
Regulate
Start tACT,
Set CHARGE
COMPLETE
state
No
State
ACTIVATION
Set
ACTIVATION
state
Check battery
temperature
Yes
Set WAIT FOR
TEMPERATURE
state
No
Check
timeouts
Yes
Set ERROR state
and error code
Yes
Set ERROR state
and error code
Yes
Set ERROR state
and error code
No
Check for
voltage error
Vb≥Vmax
No
Check for
voltage error
Ich≥Imax
No
Check rapid
start condition
Vb>=VRS
Yes
Set RAPID state
Start tRAP time
counter
No
A
www.cypress.com
B
Document No. 001-55102 Rev. *E
25
PSoC® 1 Single Cell Li-Ion Battery Charger with CY8C21x23
A
State
RAPID
B
Yes
Set Ireg=IRAP;
Regulate
No
Check
Vb>=VFULL
Yes
Set
fConstVoltage flag
Start tVCONST time
No
Check charge
terminate
condition
Yes
Set CHARGE
COMPLETE state
No
Check battery
temperature
Yes
Set WAIT FOR
TEMPERATURE
state
No
Check
timeouts
Yes
Set ERROR state
and error code
Yes
Set ERROR state
and error code
Yes
Set ERROR state
and error code
No
Check for
voltage error
Vb≥Vmax
No
Check for
current error
Ich>=IMAX
No
State
CHARGE
COMPLETE
Yes
Charge Off
Yes
Charge Off
WAIT FOR
TEMPERATURE
Set
INITIALIZATION
state
Start tACT,
Temperature
back to norm
Set
INITIALIZATION
state
Start tACT,
No
No
State
ERROR
Yes
No
No
State
Check charge
restart
condition
Yes
Charge Off
No
www.cypress.com
Document No. 001-55102 Rev. *E
26
PSoC® 1 Single Cell Li-Ion Battery Charger with CY8C21x23
Document History
®
Document Title: AN55102 – PSoC 1 Single Cell Li-Ion Battery Charger with CY8C21x23
Document Number: 001-55102
Revision
ECN
Orig. of
Change
Submission
Date
Description of Change
**
2752862
YARA
08/18/2009
New application note
*A
3210386
YARA
03/30/2011
1. Modified the schematic to show the 8-pin implementation
2. Added BOM for 8 pin implementation
3. Updated the project to PD 5.1
4. Updated the Title and Abstract.
5. Added a folder called Charge Control Center, which was earlier accessible
through AN2267, to make this AN stand-alone.
*B
3271365
YARA
06/01/2011
Document title updated as per template.
*C
3510163
RJVB
01/27/2012
Schematic and block diagram updated
Updated project with PD5.2
Updated template
*D
3704640
DESH
08/06/2012
No change. Completing sunset review.
*E
4764533
ASRI
05/14/2015
Updated Schematic diagram for CY8C21123
Added Schematic diagram for CY8C21223
Updated project with PD5.4
Updated template
www.cypress.com
Document No. 001-55102 Rev. *E
27
PSoC® 1 Single Cell Li-Ion Battery Charger with CY8C21x23
Worldwide Sales and Design Support
Cypress maintains a worldwide network of offices, solution centers, manufacturer’s representatives, and distributors. To find
the office closest to you, visit us at Cypress Locations.
PSoC® Solutions
Products
Automotive
cypress.com/go/automotive
psoc.cypress.com/solutions
Clocks & Buffers
cypress.com/go/clocks
PSoC 1 | PSoC 3 | PSoC 4 | PSoC 5LP
Interface
cypress.com/go/interface
Cypress Developer Community
Lighting & Power Control
cypress.com/go/powerpsoc
Memory
cypress.com/go/memory
PSoC
cypress.com/go/psoc
Touch Sensing
cypress.com/go/touch
USB Controllers
cypress.com/go/usb
Wireless/RF
cypress.com/go/wireless
Community | Forums | Blogs | Video | Training
Technical Support
cypress.com/go/support
PSoC is a registered trademark and PSoC Creator is a trademark of Cypress Semiconductor Corp. All other trademarks or registered trademarks
referenced herein are the property of their respective owners.
Cypress Semiconductor
198 Champion Court
San Jose, CA 95134-1709
Phone
Fax
Website
: 408-943-2600
: 408-943-4730
: www.cypress.com
© Cypress Semiconductor Corporation, 2009-2015. The information contained herein is subject to change without notice. Cypress Semiconductor
Corporation assumes no responsibility for the use of any circuitry other than circuitry embodied in a Cypress product. Nor does it convey or imply any
license under patent or other rights. Cypress products are not warranted nor intended to be used for medical, life support, life saving, critical control or
safety applications, unless pursuant to an express written agreement with Cypress. Furthermore, Cypress does not authorize its products for use as
critical components in life-support systems where a malfunction or failure may reasonably be expected to result in significant injury to the user. The
inclusion of Cypress products in life-support systems application implies that the manufacturer assumes all risk of such use and in doing so indemnifies
Cypress against all charges.
This Source Code (software and/or firmware) is owned by Cypress Semiconductor Corporation (Cypress) and is protected by and subject to worldwide
patent protection (United States and foreign), United States copyright laws and international treaty provisions. Cypress hereby grants to licensee a
personal, non-exclusive, non-transferable license to copy, use, modify, create derivative works of, and compile the Cypress Source Code and derivative
works for the sole purpose of creating custom software and or firmware in support of licensee product to be used only in conjunction with a Cypress
integrated circuit as specified in the applicable agreement. Any reproduction, modification, translation, compilation, or representation of this Source
Code except as specified above is prohibited without the express written permission of Cypress.
Disclaimer: CYPRESS MAKES NO WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, WITH REGARD TO THIS MATERIAL, INCLUDING, BUT
NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. Cypress reserves the
right to make changes without further notice to the materials described herein. Cypress does not assume any liability arising out of the application or
use of any product or circuit described herein. Cypress does not authorize its products for use as critical components in life-support systems where a
malfunction or failure may reasonably be expected to result in significant injury to the user. The inclusion of Cypress’ product in a life-support systems
application implies that the manufacturer assumes all risk of such use and in doing so indemnifies Cypress against all charges.
Use may be limited by and subject to the applicable Cypress software license agreement.
www.cypress.com
Document No. 001-55102 Rev. *E
28
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF

advertising