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LTC2942CDCB

Battery Gas Gauge with Temperature, Voltage Measurement

Linear Technology 

LTC2942

OPERATION

Overview

The LTC2942 is a battery gas gauge device designed for

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

terminal voltage at 2.7V to 5.5V. It measures battery charge

and discharge, battery voltage and chip temperature.

A precision coulomb counter integrates current through a

sense resistor between the battery’s positive terminal and

the load or charger. Battery voltage and on-chip temperature

are measured with an internal 14-bit/10-bit ADC.

Coulomb Counter

Charge is the time integral of current. The LTC2942 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 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.

Voltage and Temperature ADC

The LTC2942 includes a 14-bit No Latency ΔΣ analog-to-

digital converter, with internal clock and voltage reference

circuits.

The ADC can either be used to monitor the battery voltage

at SENSE– or to convert the output of the on-chip tempera-

ture sensor. The sensor generates a voltage proportional to

temperature with a slope of 2.5mV/K resulting in a voltage

of 750mV at 27°C.

Conversion of either temperature or voltage is triggered

by setting the control register via the I2C interface. The

LTC2942 features an automatic mode where a voltage and

a temperature conversion are executed every two seconds.

At the end of each conversion the corresponding registers

are updated and the converter goes to sleep to minimize

quiescent current.

CHARGER

LOAD

VCC

SENSE+

S1

1

S2

RSENSE

S3

SENSE–

IBAT

6

S4

+

BATTERY

GND

2

REFHI +

–

–

+

+

REFLO –

CONTROL

LOGIC

M

PRESCALER

ACR

POLARITY

DETECTION

2942 F02

Figure 2. Coulomb Counter Section of the LTC2942

2942f

7

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