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LT8584EFE

2.5A Monolithic Active Cell Balancer with Telemetry Interface

Linear Technology 

Timing Diagram

LT8584

DIN

RTMR

DCHRG

tRST

t2

t1

SR

t3

t4

tW

t6

t5

8584 TD

Operation

Many systems use multiple battery cells connected in se-

ries to increase the available capacity and voltage. In such

systems, the individual battery cells must be constantly

monitored to ensure that they operate within a controlled

range. Otherwise, the battery’s capacity and life span may

be compromised. Linear Technology offers the LTC680x

family series of multicell battery stack monitors (BSM) to

accomplish this task.

The LTC680x monitors each individual cell in the stack

and communicates this information through a proprietary

serial bus to a central processing unit. As a cell begins to

reach the upper charge limit, commands are issued to the

LTC680x to turn on that cell’s passive shunt, bypassing

the charging current to that cell and allowing the current to

continue to the rest of the cells. The passive shunt current

and/or power capability constrains the maximum charging

current for the battery stack. Using a passive shunt is also

inefficient, and the shunted current produces considerable

heat at higher charging currents.

The LT8584 solves the two limitations of passive shunting

balancers by actively shunting the charging current and

returning the energy back to the battery stack. Instead of

the energy being lost as heat, it is reused to charge the

rest of the batteries in the stack. The architecture of the

LT8584 also solves the problem of reduced run time when

one or more of the cells in the stack reaches the lower

safety voltage threshold before the entire stack capacity

is extracted. Only active balancing can redistribute the

charge from the stronger cells (cells with higher voltage)

to charge the weaker cells. This allows the weaker cells to

continue to supply the load, extracting greater than 96%

of entire stack capacity where passive balancing may only

extract 80%.

The LT8584 has an integrated 6A switch designed to operate

as a boundary mode flyback converter and provides 2.5A

average discharge current. The average discharge current

is also scalable by using multiple LT8584s to balance each

cell. Note that each battery in the stack requires an LT8584

active cell balancer.

The LT8584 flyback topology allows the charge to return

between any two points in the battery stack. Most applica-

tions use a module approach and return the charge to a

local set of 12 series-connected cells monitored by a 12

channel BSM IC, where the output of the flyback converter

is designated as VMODULE. The entire battery stack is then

constructed using several 12-cell modules connected in

series. A second approach is to return the charge to the

entire battery stack, where the flyback output is desig-

nated as VSTACK. A final option is to return the charge to

an auxiliary power rail, designated as VAUX.

The LT8584 has two modes of operation—selectable by

the MODE pin—that can be integrated with the LTC680x

or other battery stack system. In simple mode, the LT8584

8584fb

For more information www.linear.com/LT8584

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