MPF42791 datasheet(69/75 Pages) MPS

69 / 75 page

MPF42791 – 2 TO 16 BATTERY PACK FG W/ R DETECTION AND THERMAL MODEL

MPF42791 Rev. 1.0

MonolithicPower.com

9/19/2022

MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.

APPLICATION INFORMATION

CORE ALGORITHM

The fuel gauge core algorithm accurately

estimates

core

cell-level

and

pack-level

parameters.

These core parameters can be

found in the Fuel Gauge Output register map.

Cell Mathematical Model

Cell dynamics are influenced by multiple factors,

such

chemistry,

SOC,

current,

and

temperature.

mathematical

model

that

captures the cell’s most important dynamics is

required

accurately

measure

internal

variables.

Cell mathematical models are provided by MPS.

These models are either from a database or they

are a result of the cell characterization routine.

Cell State-of-Charge (SOC)

Cell SOC (SOC_ABS_CELLx) refers to the cell

capacity that is currently available, as a function

of the rated capacity. SOC is an unknown,

internal

variable

that

cannot

directly

measured, meaning it must be estimated using

available measurements. The MPF42791 uses

voltage,

current,

and

temperature

measurements observed over time to produce

accurate SOC estimates across a wide range of

operating conditions.

Empty State-of-Charge (SOC)

Empty SOC (EMTY_SOC_CELLx) refers to the

SOC level at which the battery pack is unable to

discharge further without reaching the voltage

cutoff limits defined in VPACK_EMTY. The

empty SOC prediction relies on the operating

conditions of the different cells, as well as the

discharge current supplied to the load, which is

specific to each application.

In addition, the MPF42791 can predict whether

the battery pack discharge is limited by the pack

or one of the cells (the cell ID is provided). This

is extremely important for accurate empty SOC

estimation in unbalanced packs, since the fuel

gauge must track the condition that limits the

battery pack discharge.

Full State-of-Charge (SOC)

Full SOC (FULL_SOC_CELLx) refers to the

SOC level at which the battery pack is unable to

charge further without leaving the safe operating

area (SOA). The full SOC prediction relies on the

operating conditions of the different cells, as well

the

constant-current/constant-voltage

(CC/CV) charging sequence, which is specific to

each application.

The MPF42791 can predict whether the battery

pack charge is limited by the pack or one of the

cells (the cell ID is provided). This is extremely

important for accurate full SOC estimation in

unbalanced packs, since the fuel gauge must

track the condition that limits the battery pack

charge.

Thermal Modeling

The MPF42791 incorporates battery thermal

modeling, which is extremely important to

account for battery self-heating.

The internal resistance of each cell causes the

cell’s temperature to rise during charge and

discharge due to the Joule heating effect. As

temperature

cells

increases,

internal

resistance decreases and this can dramatically

impact

performance,

especially

low

temperatures.

The ability to predict this temperature rise allows

the fuel gauge to determine state-of-charge

more accurately.

Pack State-of-Charge (SOC)

Pack SOC (SOC_PACK) provides the capacity,

which is a function of the available capacity given

the actual pack operating conditions. Pack SOC

relies on cell-level quantities and tracks the

remaining capacity that the battery can charge or

discharge without reaching the cutoff limits.

Pack SOC can be considered the most vital

estimate since it is typically the value shown to

the application end user.

Pack Unavailable State-of-Charge (SOC)

Pack unavailable SOC (SOC_PACK_UNAVBL)

refers to the capacity that is not available due to

the actual pack operating conditions (e.g.

mismatched

cells

and

battery

pack

configurations). Pack unavailable SOC provides

the capacity that the battery cannot use without

violating the defined SOA.

MPF42791 Datasheet(PDF) 69 Page - Monolithic Power Systems

MPF42791 Datasheet(HTML) 69 Page - Monolithic Power Systems

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