Compact, Low-Cost 1S/2S Fuel Gauges

with Low-Battery Alert

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7

IC Power-Up

When the battery is first inserted into the system, there

is no previous knowledge about the battery’s SOC. The

IC assumes that the battery has been in a relaxed state

for the previous 30min. The first A/D voltage measure-

ment is translated into a best “first guess” for the SOC.

Initial error caused by the battery not being in a relaxed

state fades over time, regardless of cell loading follow-

ing this initial conversion. Because the SOC determina-

tion is convergent rather than divergent (as in a

coulomb counter), this initial error does not have a long-

lasting impact.

Quick-Start

A quick-start allows the MAX17043/MAX17044 to restart

fuel-gauge calculations in the same manner as initial

power-up of the IC. For example, if an application’s

power-up sequence is exceedingly noisy such that

excess error is introduced into the IC’s “first guess” of

SOC, the host can issue a quick-start to reduce the

error. A quick-start is initiated by a rising edge on the

QSTRT pin, or through software by writing 4000h to the

MODE register.

ALERT Interrupt

The MAX17043/MAX17044 have an interrupt feature

that alerts a host microprocessor whenever the cell's

state of charge, as defined by the SOC register, falls

below a predefined alert threshold set at address 0Dh

of the CONFIG register.

When an alert is triggered, the IC drives the ALRT pin to

logic-low and sets the ALRT bit in the CONFIG register

to logic 1. The ALRT pin remains logic-low until the host

software writes the ALRT bit to logic 0 to clear the inter-

rupt. Clearing the ALRT bit while SOC is below the alert

threshold does not generate another interrupt. The SOC

register must first rise above and then fall below the alert

threshold value before another interrupt is generated.

Note that the alert function is not disabled at IC power-

up. If the first SOC calculation is below the threshold

setting, an interrupt is generated. Entering Sleep mode

does not clear the interrupt.

Sleep Mode

Holding both SDA and SCL logic-low forces the

MAX17043/MAX17044 into Sleep mode. While in Sleep

mode, all IC operations are halted and power drain of

the IC is greatly reduced. After exiting Sleep mode,

fuel-gauge operation continues from the point it was

halted. SDA and SCL must be held low for at least 2.5s

to guarantee transition into Sleep mode. Afterwards, a

rising edge on either SDA or SCL immediately transi-

tions the IC out of Sleep mode.

Alternatively, Sleep mode can be entered by setting the

communication. If the SLEEP bit is set to logic 1, the

only way to exit Sleep mode is to write SLEEP to logic 0

or power-on reset the IC.

Power-On Reset (POR)

Writing a value of 5400h to the COMMAND register caus-

es the MAX17043/MAX17044 to completely reset as if

power had been removed. The reset occurs when the last

bit has been clocked in. The IC does not respond with an

Registers

All host interaction with the MAX17043/MAX17044 is

handled by writing to and reading from register loca-

tions. The MAX17043/MAX17044 have six 16-bit regis-

ters: SOC, VCELL, MODE, VERSION, CONFIG, and

COMMAND. Register reads and writes are only valid if

all 16 bits are transferred. Any write command that is

terminated early is ignored. The function of each regis-

ter is described as follows. All remaining address loca-

tions not listed in Table 1 are reserved. Data read from

reserved locations is undefined.

ADDRESS

(HEX)

REGISTER

DESCRIPTION

READ/

WRITE

DEFAULT

(HEX)

02h–03h

VCELL

Reports 12-bit A/D measurement of battery voltage.

R

—

04h–05h

SOC

Reports 16-bit SOC result calculated by ModelGauge algorithm.

R

—

06h–07h

MODE

Sends special commands to the IC.

W

—

08h–09h

VERSION

Returns IC version.

R

—

0Ch–0Dh

CONFIG

Battery compensation. Adjusts IC performance based on

application conditions.

R/W

971Ch

FEh–FFh

COMMAND

Sends special commands to the IC.

W

—

Table 1. Register Summary