AS8506 datasheet(77/89 Pages) AMSCO

77 / 89 page

ams Datasheet, Confidential:2013-Sep [1-00]

AS8506 – 77

Appl icatio n I n f o rm a t i o n

Passive balance

Passive balance is to dissipate the energy from the cell with the

higher cell voltage to the reference value (average of the stack

e.g. max cell voltage in constant voltage charge phase or mean

cell voltage as genertaed by resitor divider).

Resistor value should be selected based on the cell chemistry

and voltage limits. Maximum current capability of internal

shuttle switch is 100mA. Internal resistance of the shuttle

switch typically is 5

Ω..

Active balance

In the active balance device charge the cells which are lower

than the reference voltage. This is a method of charge transfer

from the stack to the cell.

Flyback converter is used for this charge transfer. Active

balancing mode need to be enabled by factory setting. It is not

available for the default ASSP.

Flyback Converter (with external Transformer)

The high-efficiency, high-voltage, DC-DC Flyback converter

delivers current of 100mA to the lithium ion cell when the

secondary side of the Flyback transformer is connected to the

cell terminals. This also gives the isolation between the primary

supply and the load cell. The Flyback converter is designed to

charge the lithium-ion battery cells during the balancing mode

of the IC. It consists of a PWM waveform generator with variable

duty cycle and a driver. This driver can drive an external

MOSFET, (or) the optocoupler, (or) an isolation device based on

the requirement. During the ON-state of the PWM waveform,

the primary side of the Flyback transformer conducts and stores

the energy. In the other phase the stored energy in the

secondary is transferred to the cell which will be connected to

the secondary side of the transformer. The converter always

works in discontinuous current mode (DCM).

The advantages of this type of control system can be

summarized as following:

• High-efficiency even at light load

• Intrinsically stable

• Simplicity

Figure 100:

External Components

Component

Manufacturer Part Number

Manufacturer

Transformer

WE-FLEX 749196111

WURTH ELECTRONICS

Optocoupler

ACPL-M72T-000E

AVAGO TECHNOLOGIES

AS8506 Datasheet(PDF) 77 Page - ams AG

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