ATEVK527 Atmel, ATEVK527 Datasheet - Page 4

• Manufacturer Part Number: ATEVK527
• Description: KIT EVAL PWM AVR USB 4 SERIES
• Manufacturer: Atmel
• Series: AVR®r

Specifications of ATEVK527

• Main Purpose: Power Management, Battery Charger
• Embedded: Yes, MCU, 8-Bit
• Utilized Ic / Part: ATmega16U4, ATmega32U4
• Primary Attributes: 1 Cell- Li-Ion
• Secondary Attributes: Graphical User Interface, USB Interface
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

3 Theory of Operation
3.1 Li-Ion Battery Technology
3.1.1 Safety
4
AVR146
Battery charging is made possible by a reversible chemical reaction that restores
energy in a chemical system. Depending on the chemicals used, the battery will have
certain characteristics. A detailed knowledge of these characteristics is required in
order to avoid inflicting damage to the battery.
Lithium-Ion batteries have the highest energy/weight and energy/space ratios of
modern rechargeable batteries (See Reference 1 on page 34). It is currently the
fastest growing battery system on the market, with end applications such as notebook
computers, cell phones, portable media players, Personal Digital Assistants (PDA),
power tools and medical devices.
Compared to traditional rechargeable batteries, Li-Ion batteries have low internal
resistance, high cycle life, fast charge time, low self-discharge, low toxicity and no
maintenance requirements. For example, lithium-ion cells with cobalt cathodes hold
twice the energy of a nickel-based battery and four-times that of lead acid. Lithium-ion
is a low maintenance system, an advantage that most other chemistries cannot claim.
There is no memory effect with lithium-ion and the battery does not require scheduled
cycling to prolong its life. Lithium-ion has a low self-discharge and is environmentally
friendly. Disposal causes minimal harm.
Drawbacks of Li-Ion batteries include low tolerance of overcharge and the need for
embedded protection circuitry. An electrical short can result in a large current flow, a
temperature rise and thermal runaway in which flaming gases are vented.
Lithium-ion batteries are safe, provided certain precautions are met when charging
and discharging. In addition, battery manufacturers ensure a high level of reliability by
adding three layers of protection, as follows:
1. The amount of active material is limited to achieve a workable equilibrium of
2. Various safety mechanisms are included within each cell.
3. An electronic protection circuit is added inside the battery pack.
Cell protection devices work as follows:
• A PTC/NTC (positive/negative temperature coefficient) device acts as a protection
• The CID (circuit interrupt device) opens the electrical path if an excessively high
• The safety vent allows a controlled release of gas in the event of a rapid increase
energy density and safety.
to inhibit high current surges.
charge voltage raises the internal cell pressure.
in cell pressure.
7801A-AVR-06/08