Transcript
Application Note 71301
Li-ion Battery Pack Design
Abstract This design note shows how to build a USB rechargeable Li-ion battery pack using the linear battery charger IC CS7R3831 and step-up DC/DC converter CS7D9066. The application makes use of standard USB as power source to charge 3.7V Li-ion batteries (with 4.2V charging voltage) with a maximum charging current of 500mA (standard USB port current limit). When the USB power source is connected, the Li-ion batteries will be disconnected from the DC/DC converter and the output. When the USB power source is detached, the Li-ion batteries will automatically connect to the DC/DC converter, which will provide a 5V output with maximum 500mA output current (standard USB port current output) available to external devices via the output USB port. The application also provides charging, full charge and Li-ion battery fail LED status display. Multiple DC/DC converter can be applied, in case multiple outputs are desired. The application provides on-demand output current supply, with very low stand-by current consumption to achieve long stand-by period after each charge.
Introduction USB battery packs are small, portable rechargeable batteries that recharge any USB devices, such as phones, tablets, etc. They range in physical size, capacity, number of outputs and price. In this application note, Canaan will introduce an USB battery pack solution for the market with both cost and efficiency advantage. The most important specification for any USB battery pack is its “mAh” which stands for milliampere-hour. This is how much charge the battery stores. Apple’s iPhone 5 has 1440mAh, while the latest iPad has a massive 42500mAh battery. The Canaan solution can work with Li-ion battery pack with any desired capacity to fulfill the USB battery pack market that you desired. Furthermore, Canaan’s solution is capable of speed charging the battery pack Li-ion battery with 0.8A input, which significantly shortens the charging time (and at the same time fulfill the maximum charging rate of modern Li-ion battery without requiring the application of any special batteries). Canaan’s USB battery pack solution provides an on-demand output current supply with 500mA maximum output current and low standby current to preserves battery charge. Furthermore, multiple output ports, each with 500mA maximum output current is readily available with the minimum increase in components and circuit size. Multiple output ports will allow charging multiple devices at once. Canaan’s USB battery pack solution also comes with 2 LED lights that indicate “charging”, “full charge” and “battery failure” status to provide better user interface.
Control logic
USB Power input
Programmable USB charger (1A max) Charging / Battery Fault
5V 500mA DC/DC converter
USB Power output
5V 500mA DC/DC converter
Additional USB power Output port
Full Charge
Page 1
Application Note 71301
Rev A. Nov 2013
Li-ion Battery Pack Design
AN71301
AN71301 Canaan Semiconductor
Rev A. Nov 2013
Reference Schematic
The battery pack output voltage (VOUT) is designed to be 5V, such as to support USB powered devices. The output voltage can be adjusted by following VOUT=(1+R4/R5)*2.5V. It should be noted that the possible range of VOUT depends on the re-chargeable battery voltage and it should always be less than 6V. CS7D9066 has on-demand charge pump output control, and low standby current. A high resistance of R4 and R5 is desired to lower the standby power. A standby current reference for the reference schematic is less than 520uA. The maximum output with VOUT at 5V is larger than 500mA where a 10ohm loading resistor is connected in between VOUT and GND. This output current and voltage can be achieved even when the Li-ion battery voltage dropped to 2V in our reference design. Noted that the higher values of R4 and R5 will form “high impedance loops” which are sensitive to interference, thus requiring careful layout to avoid any interference, e.g. probing to FB pin. The VOUT is float when supply voltage VCC is connected (via USB power source). The battery charging current is controlled by R6 which follow ICHARGE=(1000/R6)A. The reference circuit is designed with 500mA charging current, while a maximum of 800mA charging current can be provided by adjusting R6. The charging time depends on the battery specification. Noted that the charging algorithm of CS7R3831 is constant current charging when the Li-ion battery has low storing capacitive, and automatically switch to constant voltage charging when the Li-ion battery has high storing capacitive such as to increase the battery life. Therefore the charging time will not be equal to mAh/ICHARGE. As a rule of thumb, it will be 2.5x of the computed mAh/ICHARGE. When the reference design is applied with an empty 700mAh Li-ion battery with R6=2Kohm (i.e. 500mA charging current), the total charging time to achieve a fully charged battery is 3hrs 40mins. The LED lamps, D1 and D2, indicate the charger operating conditions, where D1
D2
Flickering
Dimmed
USB power in with Battery connected and charging
On
Off
USB power in with Battery connected and fully charged
On
On
USB power in with Battery fault/ no connected
The reference design will draw 500mA from USB power in to charge the Li-ion battery with low storing capacitive. The reference design will draw less than 800uA from USB power in after the Li-ion battery has been fully charged. This application circuit provide no battery short-circuit and under-voltage protection. External protection circuits are required Page 2
AN71301 Canaan Semiconductor
Rev A. Nov 2013
Bill of Materials Part
Value
Description
Source
C1
10u
Chip Ceramic Capacitor
Variety
C2
1uF
Chip Ceramic Capacitor
Variety
C3
10uF
Chip Ceramic Capacitor
Variety
C4
10uF
Chip Ceramic Capacitor
Variety
C5
10uF
Chip Ceramic Capacitor
Variety
D1
LED
General Purpose LED Light
Variety
D2
LED
General Purpose LED Light
Variety
L1
10uH
Coil Inductor (Rated Current: 0.5A~1.5A)
Variety
Q1
CS9N2301
P-Channel MOSFET 20V 3A
Canaan
R1
1k
Chip Resistor
Variety
R2
1k
Chip Resistor
Variety
R3
100k
Chip Resistor
Variety
R4
1.02M
Chip Resistor
Variety
R5
332k
Chip Resistor
Variety
R6
2k
Chip Resistor
Variety
U1
CS7R3831
Integrated Linear Li-ion Battery Charger
Canaan
U2
CS7D9066
500mA PWM Synchronous Step-Up DC-DC Converter
Canaan
Page 3
AN71301 Canaan Semiconductor
Rev A. Nov 2013
Summary
A low cost, high efficiency, with added advantage USB battery pack solution is disclosed in this application note. Canaan’s solution can be applied in low capacity USB battery pack as premium solution, or heavy duty power solution for professionals. A revision of the application note, AN71302, will disclose the addition of a push button triggered LED arrays to display the battery power stored in the Li-ion battery within the USB battery pack, such that the user can have a clear visual observation on the amount of juicy left in the battery pack before determining if it can fulfill the user’s application requirement before the next recharge. This application circuit provide no battery short-circuit and under-voltage protection. External protection circuits are required
Additional Information For technical questions and application information: Please contact our application engineers.
Page 4
AN71301 Canaan Semiconductor
Rev A. Nov 2013
Revision History Date
Rev
Description
November 2013
A
First Release
Page 5
AN71301 Canaan Semiconductor
Rev A. Nov 2013
IMPORTANT NOTICE The information presented in this document does not form part of any quotation or contract, is believed to be accurate and reliable. Canaan Semiconductor (CS) does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied. CS reserves the right to make changes to its products or to discontinue any integrated circuit product or service without notice, and advises its customers to obtain the latest version of relevant information to verify, before placing orders, that the information being relied on is current. No liability will be accepted by CS for any consequence of its use. A few applications using integrated circuit products may involve potential risks of death, personal injury, or severe property or environmental damage. CS integrated circuit products are not designed, intended, authorized, or warranted to be suitable for use in lifesupport applications, devices or systems or other critical applications. Use of CS products in such applications is understood to be fully at the risk of the customer. In order to minimize risks associated with the customer’s applications, the customer should provide adequate design and operating safeguards.
Headquarter Canaan Semiconductor Limited Unit 8, 12/F, Wah Yiu Industrial Centre 30-32 Au Pui Wan Street Fotan, Shatin, N.T. HONG KONG Tel : (852)-3619-6533
Page 6
