L9963E datasheet(101/184 Pages) STMICROELECTRONICS

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4.13

Coulomb counting routine

4.13.1

Coulomb counting

The Coulomb counting routine is performed to evaluate the charge injected / subtracted during vehicle operation.

To enable it, the CoulombCounter_en bit must be set to ‘1’.

Disabling the Coulomb Counter by setting CoulombCounter_en to ‘0’ doesn’t reset the accumulator

(CoulombCounter_msb, CoulombCounter_lsb) and sample counter (CoulombCntTime) registers. MCU is

supposed to reset the Coulomb Counter, clearing any data previously stored, before enabling it.

This can be done by performing a burst read operation as explained below:

•

When L9963E is in Normal state, current is continuously sampled: a new conversion starts as soon as the

previous one has been completed. Each acquisition window lasts TCYCLEADC_CUR. Coulomb counter

internal registers are accessible sending the 0x7B command via SPI (refer to Table 23) and are updated at

the end of each conversion.

–

To read the Coulomb Counter internal registers:

◦

MCU sends the 0x7B burst command (see Table 26).

◦

At command receival, data is loaded from accumulator (CoulombCounter_msb and

CoulombCounter_lsb) and sample counter (CoulombCntTime) registers and L9963E will

answer with a burst containing also instantaneous current (CUR_INST_calib) and diagnostic data

(CoCouOvF).

◦

Meanwhile, both the accumulator and the sample counter are reset to zero.

◦

MCU can then evaluate the charge variation ΔQ in the battery pack, by referring to a known

previous state of charge Q(t0) and applying the following equation:

Coulomb Counting algorithm

Qtk =Qt0+∆Q=Qt0+∆T∑k=1KICELLk =Qt0+ ∆TRSHUNT∑k=1KVDIFF_CUR_SENSEk

∆T=TCYCLEADC_CUR

K=CoulombCntTime

∑k=1KVDIFF_CUR_SENSEk = CoulombCountermsb+CoulombCounterlsb 2′s compl*VISENSE_RES

(17)

◦

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

–

MCU must periodically read the Coulomb Counter in order to avoid accumulator or sample counter

overflow (latched by CoCouOvF bit). In case a register overflows, it will saturate: CoulombCntTime

saturates to 0xFFFF, while CoulombCounter_msb/lsb saturates either to the upper bound

(0x7FFFFFFF) or to the lower bound (0x80000000). In case of saturation, activity will continue, but

data will not be reliable. Recommended polling period is 1 s or less.

–

Reading the Coulomb Counter registers will not interrupt the Coulomb Counting Routine running in

background.

–

If a current sample (absolute value) overcomes ICURR_SENSE_OC_NORM (programmable via SPI in

the adc_ovc_curr_threshold_norm register), the curr_sense_ovc_norm flag is set and FAULTL pin

is risen. This functionality is meant to detect overcurrent events that could damage the battery pack

when the system ignition is ON.

–

This check can be masked by programming ovc_norm_msk = 1.

•

When L9963E is in Cyclic Wakeup state, current is continuously sampled while the device is in the ON

phase. If a current sample (absolute value) overcomes ICURR_SENSE_OC_SLEEP (programmable via SPI

in the adc_ovc_curr_threshold_sleep register), the curr_sense_ovc_sleep flag is set, L9963E moves to

Normal state and FAULTL pin is risen. This functionality is meant to detect anomalous current leakage from

the battery pack when the system ignition is OFF.

–

This check can be masked by programming ovc_sleep_msk = 1.

When L9963E operates in Cyclic Wakeup and the Coulomb Counter is enabled, the ON phase ends when the

Voltage Conversion Routine is over (DUTY_ON = ‘0’) and the Coulomb Counter has acquired at least one current

sample.

L9963E

Coulomb counting routine

DS13636 - Rev 12

page 101/184

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