LTC2941-1 View Datasheet(PDF) - Linear Technology

Part Name

Description

MFG CO.

LTC2941-1

1A I2C Battery Gas Gauge with Internal Sense Resistor

Linear Technology 

LTC2941-1

Operation

Overview

The LTC2941-1 is a battery gas gauge device designed for

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

terminal voltages from 2.7V to 5.5V. A precision coulomb

counter integrates current through an internal sense resis-

tor between the battery’s positive terminal and the load or

charger. The integrated, temperature-compensated sense

resistor offers board space savings and superior charge

measurement accuracy in applications with currents up

to 1A.

Coulomb Counter

Charge is the time integral of current. The LTC2941-1 mea-

sures battery current by monitoring the voltage developed

across its internal sense resistor and then integrates this

information to infer charge. The internal sense resistor is

tied between the SENSE+ and SENSE– pins and is con-

nected to an auto-zeroed differential analog integrator

which converts the measured current to charge.

When the integrator output reaches the REFHI or REFLO

thresholds, 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 effectively increases integration

time by a factor M programmable from 1 to 128. At each

underflow or overflow of the prescaler, the accumulated

charge register (ACR) value 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 LTC2941-1 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.

CHARGER

LOAD

VSUPPLY

IBAT

+

BATTERY

SENSE+

S1

1

RBOND

RSENSE

S2

S3

SENSE–

6

RBOND

S4

GND

2

REFHI +

–

–

+

+

REFLO –

CONTROL

LOGIC

POLARITY

DETECTION

PRE-

SCALER

M

STATUS

CONTROL

REGISTERS

ACR

THRESHOLDS

AL/CC

5

I2C/

SMBus

SCL

3

SDA

4

29411 F03

Figure 3. Coulomb Counter Section of the LTC2941-1

29411f



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