L9963E datasheet(48/184 Pages) STMICROELECTRONICS

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The schematic of the external balancing is shown in the figure above.

The cell stack can be divided into adjacent couples and, for each couple, the even cell is balanced by a PMOS,

while the odd cell is balanced by an NMOS.

For further information refer to Section 6.6.2 Cell balancing with external MOSFETs.

4.7.3

Balancing modes

In order to allow maximum flexibility, the cell balancing process can be performed both in Manual Balancing

mode and Timed Balancing mode. The configuration can be selected by acting on Balmode bit.

In case balancing is interrupted by Voltage Conversion Routine, any unfinished balancing state will be saved,

and will resume once the measurement is done.

It is started writing bal_start = 1 and bal_stop = 0, while it can be stopped by writing the opposite code

(bal_start = 0 and bal_stop = 1). Writing other codes will not alter the status of balancing. Switching from

Manual Balancing mode to Timed Balancing mode will immediately apply the new settings. Balancing will not

be interrupted, unless ThrTimedBalCellxx is set to ‘0’ for a specific cell, causing the immediate end of balancing

on it.

The bal_on and eof_bal flags indicate the status of the balancing FSM. Once a balancing task is over MCU must

program bal_start = 0 and bal_stop = 1 in order to reset the FSM to the idle state.

Table 42. Balancing FSM

bal_on

eof_bal

Balancing Status

Idle

Balancing Over

Ongoing

Impossible

Note that balancing is performed only on enabled cells (VCELLx_EN = 1). Once balance is started, any change to

VCELLx_EN or BALx will not disable the balancing function on the related cell. To disable balancing, bal_start =

0 and bal_stop = 1 must be programmed.

4.7.3.1

Manual balancing mode

The MCU directly controls the output state of Sn (n=1…14) individually. The start and end time of the balancing

are controlled by bal_start and bal_stop.

To operate manual balancing, follow these steps:

Set Balmode = 01 in the Bal_2 register to configure manual balancing

Set BALxx = 10 in the BalCell14_7act and BalCell6_1act registers to enable balancing on the selected

cells

Set bal_start = 1 and bal_stop = 0 in the Bal_1 register to start balancing

To prevent cell overdischarge due to misconfiguration, Manual Balancing does not support the Silent Balancing

state. Any GO2SLP command or communication timeout will halt the operation and move L9963E to the Sleep

mode, even if slp_bal_conf flag is set. Balancing will not be resumed once the device is woken up.

In order to prevent cells over-discharge, a watchdog timer WDTimedBalTimer, whose timeout is TBAL_TIMEOUT,

is always started at the beginning of each manual balancing start command. In case the timeout expires, the

balancing is stopped and the EoBtimeerror latch is set. FAULT line will also be triggered.

4.7.3.2

Timed balancing mode

The device is able to balance at the same time up to 14 cells. The balancing procedure is the following:

Set Balmode = 10 in the Bal_2 register to configure timed balancing;

The MCU can program up to 14 registers (ThrTimedBalCellxx) to assign each cell with its own balancing

time duration, based on the estimation of the charge to be subtracted;

Set BALxx = 10 in the BalCell14_7act and BalCell6_1act registers to enable balancing on the selected

cells;

Set bal_start = 1 and bal_stop = 0 in the Bal_1 register to start balancing.

L9963E

Cell balancing

DS13636 - Rev 12

page 48/184

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