MAX17040 Просмотр технического описания (PDF) - Maxim Integrated

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MAX17040

1-Cell/2-Cell Fuel Gauge with ModelGauge

Maxim Integrated 

MAX17040/MAX17041

1-Cell/2-Cell Fuel Gauge with ModelGauge

compared to traditional coulomb counters, which suffer

from SOC drift caused by current-sense offset and cell

self-discharge. This model provides good performance

for many Li+ chemistry variants across temperature and

age. To achieve optimum performance, the MAX17040/

MAX17041 must be programmed with configuration data

custom to the application. Contact the factory for details.

Fuel-Gauge Performance

The classical coulomb-counter-based fuel gauges suffer

from accuracy drift due to the accumulation of the offset

error in the current-sense measurement. Although the

error is often very small, the error increases over time in

such systems, cannot be eliminated, and requires peri-

odic corrections. The corrections are usually performed

on a predefined SOC level near full or empty. Some other

systems use the relaxed battery voltage to perform cor-

rections. These systems determine the true SOC based

on the battery voltage after a long time of no activity. Both

have the same limitation: if the correction condition is not

observed over time in the actual application, the error in

the system is boundless. In some systems, a full charge/

discharge cycle is required to eliminate the drift error. To

determine the true accuracy of a fuel gauge, as expe-

rienced by end users, the battery should be exercised

in a dynamic manner. The end-user accuracy cannot

be understood with only simple cycles. The MAX17040/

MAX17041 do not suffer from the drift problem since they

do not rely on the current information.

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 measurement 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 following this initial

conversion. Because the SOC determination is conver-

gent 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 MAX17040/MAX17041 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 EO pin when SEO

is logic-low, or through software by writing 4000h to the

MODE register.

External Oscillator Control

When the SEO pin is logic-high, the MAX17040/

MAX17041 disable the 32kHz internal oscillator and rely

on external clocking from the EO pin. A precision external

clock source reduces current consumption during normal

operation.

When the SEO pin is logic-low, the EO pin becomes an

interrupt input. Any rising edge detected on EO causes

the MAX17040/MAX17041 to initiate a quick-start.

Sleep Mode

Holding both SDA and SCL logic-low forces the MAX17040/

MAX17041 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 transitions the IC out of Sleep mode.

Power-On Reset (POR)

Writing a value of 0054h to the COMMAND register

causes the MAX17040/MAX17041 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 I2C ACK after this command sequence.

Registers

All host interaction with the MAX17040/MAX17041 is han-

dled by writing to and reading from register locations. The

MAX17040/MAX17041 have six 16-bit registers: SOC,

VCELL, MODE, VERSION, RCOMP, 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 register is described

as follows. All remaining address locations not listed in

Table 1 are reserved. Data read from reserved locations

is undefined.

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