LTC2941CDCB datasheet(7/16 Pages) LINER

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LTC2941

2941f

OPERATION

Overview

The LTC2941 is a battery gas gauge device designed for

use with single Li-Ion cells and other battery types with

a terminal voltage between 2.7V and 5.5V. A precision

coulomb counter integrates current through a sense

resistor between the battery’s positive terminal and the

load or charger.

Coulomb Counter

Charge is the time integral of current. The LTC2941 mea-

sures battery current by monitoring the voltage developed

across a sense resistor and then integrates this information

to infer charge. The differential voltage between SENSE+

and SENSE– is applied to an auto-zeroed differential analog

integrator to convert the measured current to charge.

When the integrator output ramps to REFHI or REFLO

levels, switches S1, S2, S3 and S4 toggle to reverse the

ramp direction. By observing the condition of the switches

and the ramp direction, polarity is determined.

A programmable prescaler is incremented or decremented

every time the integrator changes ramp direction. The

prescaler effectively increases integration time by a factor

M programmable from 1 to 128. At each under or overﬂow

of the prescaler, the accumulated charge is incremented or

decremented one count. The value of accumulated charge

is read via the I2C interface.

Power-Up Sequence

When VSENSE+ rises above a threshold of approximately

2.5V, the LTC2941 generates an internal power-on reset

(POR) signal and sets all registers to their default state.

In the default state, the coulomb counter is active. The

accumulated charge is set to mid-scale (7FFFh), the

low threshold registers are set to 0000h and all the high

threshold registers are set to FFFFh. The alert mode is

enabled and the coulomb counter pre-scaling factor M

is set to 128.

–

REFHI

REFLO

LOAD

CHARGER

SENSE+

RSENSE

BATTERY

IBAT

SENSE–

GND

POLARITY

DETECTION

CONTROL

LOGIC

PRE-

SCALER

I2C/

SMBus

REGISTERS

AL/CC

SCL

SDA

2941 F03

STATUS

CONTROL

ACR

THRESHOLDS

VSUPPLY

Figure 3. Coulomb Counter Section of the LTC2941

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