Keywords: USB interface， lithium-ion battery， charging circuit
lithium-ion battery and USB Interface
Overview
Lithium-ion (Li-ion) batteries, lithium
battery for short <http://bbs.dianyuan.com/tech/battery>, is the
increasing popularity in recent years, the use of a new type of battery, with
small size, light weight, high capacity (high energy density), self-discharge
rate and advantages such as no memory effect, but it also has some fatal flaw:
the charging and discharging of the more stringent requirements, can not
overcharge and over discharge, or likely to cause irreversible damage to, in
short circuit, overcharge and other extreme cases there may be an explosion dangerous.
General lithium single nominal voltage 316
~ 317V, charging, generally require the use of limited pressure limiting law,
the first constant current charging, ie a current constant charging current by
low magnification national standard charge is 0.2C (arbitration charge
standard), the maximum does not exceed 1C; while charging the battery voltage
is gradually increased as when the battery terminal voltage reaches the
termination voltage 412 ± 0105V, should be changed to constant voltage constant
current charging small current (about 011C) charge, the state general called
trickle charge state. The charging current based on the saturation level of the
batteries, with the charging process continues to gradually decrease, and when
reduced to 0101C, that the charging is terminated.
USB interface is in English
UniversalSerialBus abbreviation, Chinese meaning is "Universal Serial
Bus." It is a new field in the PC interface technology applications. USB
uses a 4-pin plug as a standard plug to connect with external devices. In this
four-pin plug, there are two pins for data communication lines, while the outer
two needles compared to an external device to provide power. According to the
USB specification, each USB port should be able to provide 500mA output current;
provided by the USB host or hub with a power supply of the USB interface, the
connected peripheral end of the minimum available voltage is 4.5V, while the
USB bus powered hub can provide should be a minimum of 4.35V. worth noting
that, although the USB specification defines the current limit provided shall
not exceed 015A, but in fact the current USB port output is often more than a
few amps.
As can be seen from the above analysis, the
use of USB interface for battery charge, the current terms should be enough,
the key is how to control the size of the current. In addition, the use of a
minimum of 4.35V voltage USB interface to the typical requirements for 4.2V
lithium battery when charging, only a small margin on the voltage, which makes
the charging circuit voltage drop becomes extremely important, is the
difficulty of design.
PC-based USB interface charging circuit
design
2.1 Option One
Figure 1 is a market of some of the
"USB charging cable," the internal circuitry. The main principle is
to use the maximum current limit resistor, a diode voltage drop (approximately
0.7V) about the USB interface 5V output voltage down to about 4.2V rechargeable
lithium battery then. This circuit has a simple, low-cost advantage, but the
disadvantage is obvious: the charging current and charging voltage and battery
status vary in different USB interface vary, basically can not grasp, in many
cases the battery is likely sufficient dissatisfaction (charging voltage of
less than 4.2V), but sometimes it may overcharge and damage the battery. This
circuit has some internal lithium battery protection circuit for sound
acceptable, but for ordinary lithium batteries, there are certain dangers.
2.2 Option II
Figure 2 is a practical USB Li-ion battery
charging circuit by MAX1551 / 1555 constituted. MAX1551 / 1555 is designed and
manufactured by MAXIM USB single lithium battery charging chip, 5-pin thin
SOT23 package, allowing the USB port or wall adapter 3.7V ~ 7V AC input voltage
range. Internal chip also has a temperature limit circuit.
When For this circuit, when connected to a
USB port, but no AC wall adapter DC power, the charging current is set to 100mA
(Max). This is not required in the case of the communication port, allows the
power from the USB port or power charging. When DC power is turned on, the
charging current is set to 280mA (typ), while the USB input interface is
automatically cut off. If both inputs are non-voltage input, the circuit is
automatically turned off, then the reverse leakage current of the battery is
less than 5uA, no external diode to prevent battery leakage losses occur.
When the battery voltage is lower than 3V,
will enter 40mA charge current is limited to a pre-charge mode (trickle charge
state), only when the battery is charged to 3V than when entering the normal
charging mode (100mA or 280mA). This mode protects the deep discharge battery.
Figures 3 and 4 are used as the DC power supply box curve USB interface input
voltage and the charging current of the battery.
In addition, the MAX1551 ", /
POK" is used to indicate the input power is turned on (when the input
voltage is 3.95V output low); while for MAX1555 ", / CHG" is used to
indicate the state of charge (when the charge current is greater than 50mA
output low).
2.3 Option III
It should be said, Option II is a safe,
relatively comprehensive consideration of all aspects of USB rechargeable
lithium battery and perfect solution. The disadvantage of this solution is
that: the charging current is fixed at about 100mA or 280mA, especially when
the USB interface power supply, only the charging current of 100mA for larger
capacity batteries, charging takes quite a long time. Another disadvantage is
that there is no charge timer function, the charge can not be ended or not
artificially controlled. Figure 5 is another practical USB interface charging
circuit design using the LTC4053 as the core, while maintaining the advantages
of the two programs again to solve the above problems.
LTC4053 is Linear (Linear) has introduced a
USB interface can be powered directly from a lithium-ion battery termination
constant current / constant voltage linear charger IC with Independent Timing
for 10-pin MSOP package. May consist of a single lithium battery USB interface
for charging directly, or you can allow the use of a wall AC adapter as the
power supply of DC power. Required input voltage range is 4.25V ~ 6.5V.
Includes an on-chip power MOSFET. The most important feature of this chip is
that it allows designers to set their own charging current and charging time,
charging termination voltage already preset to 4.2V.
In Figure 5, the charging current by PROG
LTC4053 (7) pin resistor R to the set, which is calculated as: R = 1500V /
ICHG, for example, to set the charging current is 500mA, then R = 1500V / 015A =
3kΩ. The maximum charging current can be set to 1125A. Figure 6 is a graph of
the charging current and battery voltage.
LTC4053's TIMER (4) capacitance C pin is
used to set the charging time is calculated as follows: T (h) = C (uF)? 3 /
011uF. When C = 011uF, the charging time of 3 hours.
This circuit has a similar program two
pre-charge mode trickle charge mode and battery-specific fault detection
function: When the battery voltage is lower than 2.48V, with 10% of full scale
current trickle charge; If this state lasts more than a quarter of the total
charge time is that the battery has been damaged and stop charging cycle.
LTC4053 itself has a perfect temperature
measurement and compensation adjustment function that allows users to safely
larger current charging thereby greatly reducing the charging time, charging
current and Figure 7 is a graph of the ambient temperature. Similarly, when the
LTC4053 no voltage input, the circuit can automatically cut-off, the reverse
leakage current is less than 5uA, no external diode to prevent battery leakage,
avoid battery depletion.
Conclusion
There is no doubt that in these three
scenarios, features the third option is the most perfect, the flexibility of
its design application is also the biggest, but more pins, the device cost of
the chip may also be higher than other programs . In practice, we can according
to the actual situation of use, cost, etc. to choose different options to meet
different requirements. With the development of integrated circuit technology,
the constant introduction of new devices, we believe there will be more and
better USB charging scheme appears.
General Electronics Battery Co., Ltd. electric vehicle battery has
been committed to the development, production, for consumers to create a safe,
environmentally friendly batteries.
Contact : Benny , SALE , Gebattery , Tel. 86-755-81762725, 81762726, 8 1762727, 23315028, 2331308 or e-mail : sell@gebattery.com.cn
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