Cypress AN2309 - Manual
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Table of Contents:
- Page 2 – Cell-Balancing Foundation; Equation 1; cellN; Equation 6
- Page 3 – Equation 7; Amount of Imbalance
- Page 4 – Cell Balancing Time; bal; Cell Capacity; mA; Two-Cell Battery Charger Hardware; constant current
- Page 5 – Figure 3
- Page 6 – Device Schematic; Figure 4; Error
- Page 8 – PSoC Device Internals; Figure
- Page 9 – Battery Measurement; meas; max; ref
- Page 10 – Figure 7
- Page 11 – Two-Cell Battery Charger Firmware; Two-Cell Battery Charger Algorithm; Figure 8
- Page 12 – Figure 9
- Page 13 – Figure 9. Two-Cell Battery Charger Firmware Flowchart Part 1
- Page 14 – Figure 10. Two-Cell Battery Charger Firmware Flowchart Part 2; Cell-Balancing Algorithm; pulse charge technique
- Page 16 – Two-Cell Battery Charger Parameters; in the project folder. The header file
- Page 17 – Cell-Balancing Parameters; All cell-balancing parameters are located in the header file; Conclusion; if users are interested in easily adding fuel
- Page 18 – Appendix; Charge/Discharge and Cell-Balancing Profile Examples; Figure 13. Charge/Discharge Manager Profile
- Page 19 – Figure 14. Cell-Balancing Activity Profile
- Page 20 – Figure 15. Cell-Balancing Parameter Profile Screen; About the Author; Oleksandr Karpin
- Page 21 – Document History; ECN; HMT
Power Management - Low-Cost, Two-Cell
Li-Ion/Li-Pol Battery Charger with
Cell-Balancing Support
November 25, 2007
Document No. 001-17394 Rev. *B
- 1 -
AN2309
Author
: Oleksandr Karpin
Associated Project
: Yes
Associated Part Family
: CY8C24x23A, CY8C24794, CY8C27x43, CY8C29x66
Software Version
: PSoC Designer
™ 5.0 SP1
Associated Application Notes
Application Note Abstract
This application note describes a low cost, two-cell Li-Ion/Li-Pol battery charger. An effective cell-balancing algorithm during
both charge and discharge phases is presented. This charger can be used either as a standalone application to charge a
battery pack with two serial connected Li-Ion/Li-Pol batteries or embedded in residential, office, and industrial applications
.
Introduction
A modern portable system requires more operating voltage
than a single-cell Lithium-ion (Li-Ion) or Lithium-polymer (Li-
Pol) battery can provide. A serial connection results in a
pack voltage equal to the sum of the cell voltages. To
increase the battery pack capacity, the cells are connected
in parallel. For many applications, two cells in series are
sufficient, with one or more cells in parallel. This
combination gives nominal voltage and the necessary power
for
laptop
computers
and
medical
and
industrial
applications. Problems can occur when the cells have
different capacities or charge levels. During charging or
discharging, the cells in the battery pack do not have
matched voltage every cell. Therefore, the battery pack is
not balanced. The unbalanced charge between cells causes
the following problems:
Reduced overall battery pack capacity to the value of
the cell with the least capacity. During the charge
process, this cell reaches the maximum charge level
before the other cells, and during the discharge process
this cell is depleted before the other cells in the pack.
Reduced overall battery pack life. The charge or
discharge of cells at different values increases pack
imbalance.
Cell damage, which occurs if the charger monitors only
the summary voltage. For example, if the lower cell has
a capacity deficiency of at least 10 percent, its cell
voltage begins to rise into the dangerous area above
4.3 volts. This can result in additional degradation of the
cell or a safety system response that greatly reduces
pack capacity.
This application note describes a two-cell Li-Ion/Li-Pol
battery charger. An effective cell-balancing algorithm is
designed. It avoids the issues that appear in battery packs
with two cells in series. Through modification of the
configuration parameters, the cell-balancing algorithm can
easily be adapted for various applications and selected
batteries. The unique architecture of the PSoC
®
device
provides an integrated hardware solution for a two-cell
battery charger and a flexible
μC
-based, cell-balancing
algorithm with minimal external components at a very
affordable price. The CY8C24x23A PSoC device family
used in this implementation reduces the total device cost
even further.
When you want to use algorithms for the latest charging or
cell-balancing technologies, only the firmware needs to be
modified. PSoC Designer’s in-circuit and self-programming
capabilities make these operations simple.
Specifications for a two-cell Li-Ion/Li-Pol battery charger with
cell-balancing support are listed in
on page 2.
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Summary
AN2309 November 25, 2007 Document No. 001-17394 Rev. *B - 2 - Table 1. Specifications for Two-Cell Li-Ion/Li-Pol Battery Charger with Cell-Balancing Support Item Item Value Battery Charger Parameters Built-In Battery Charger Type Two-cell Li-Ion/Li-Pol battery charger Power Supply Voltage 10…14V Pow...
AN2309 November 25, 2007 Document No. 001-17394 Rev. *B - 3 - Temperature gradient across the battery pack. Temperature mismatches of 15 degrees Celsius can cause up to 5- percent capacity differential among cells. Such a temperature gradient is relatively common in densely packed products, where ...
AN2309 November 25, 2007 Document No. 001-17394 Rev. *B - 4 - Cell Balancing Time : If C is the cell capacity and b V is the battery voltage, and the requirement is to eliminate the amount of imbalance (in percent) in one hour of balancing time, then the power dissipation on balancing circuit P ba...
