L9961-TR datasheet(28/65 Pages) STMICROELECTRONICS

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3.5.2

Coulomb counting

To enable the accumulation function, the CC_ACC_EN bit must be set. When Coulomb counting is active, current

samples are continuously accumulated in the CC_ACC register, while the CC_SAMPLE_CNT counts the number

of samples stored in the accumulator. Disabling the Coulomb counting will cause accumulator and sample counter

reset: to avoid loss of information, the MCU is supposed to download the Coulomb counter information before

disabling it.

MCU must periodically poll the Coulomb counter to retrieve the charge information. The following procedure has

to be implemented in order to guarantee proper data synchronization between accumulator and sample counter:

MCU writes CC_ACC_MSB register with 0xFFFF data

The accumulator is cleared upon write

A snapshot of the internal sample counter and accumulator is loaded into CC_SAMPLE_CNT,

CC_ACC_MSB and CC_ACC_LSB fields

The shadow register of the internal sample counter is in the meantime reset.

MCU reads the CC_ACC_MSB register

MCU reads the CC_ACC_LSB_CNTR register

The Coulomb counting operation requires the MCU to track the charge added/subtracted from the battery pack

over time. L9961 helps tracking the charge variation ΔQ in the battery pack by continuously acquiring and

accumulating the current. This significantly reduces the MCU reading rate, simplifying user SW.

Coulomb counting routine may refer to a known previous charge Q(t0) and apply the following equation:

Coulomb counting algorithm

Qtk =Qt0+∆Q=Qt0+∆T∑k=1KICELLk =Qt0+TCUR_FILTER

RSHUNT ∑k=1KVDIFFk

∑k=1KVDIFFk =CC_ACC*VCUR_RES

(6)

Where:

•

VDIFF = ISENSEP-ISENSEM

•

CC_ACC is the accumulator, encoded in 2’s complement

•

RSHUNT is the external shunt resistor mounted between ISENSEP and ISENSEM

Then, the Q(tk) just evaluated becomes the Q(t0) for the next iteration.

The CC_SAT read-only flag reports the status of the accumulator and sample counter: if one of the two

accumulators of the two saturates, the CC_SAT is set to ‘1’ and a RDY pulse is generated to inform MCU

that the registers data are ready. Meanwhile, the accumulation is stopped and CC_ACC and CC_SAMPLE_CNT

are frozen.

3.5.2.1

Electrical parameters

All parameters are tested and guaranteed in the following conditions, unless otherwise noted:

VB according to the operating range of Table 2; TJ according to the operating range of Table 5.

Table 19. Coulomb counter electrical parameters

Symbol

Parameter

Test conditions

Min.

Typ.

Max.

Unit

NACC

Coulomb counter accumulator size

Design info

bit

NSAMPLE_CNT

Coulomb counter sample counter

size

Design info

bit

L9961

Current conversion routine

DS14012 - Rev 3

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