LTC2943
OPERATION
Overview
Voltage, Current and Temperature ADC
The LTC2943 is a battery gas gauge designed for use
with multicell batteries with terminal voltages from 3.6V
to 20V. It measures battery charge and discharge, battery
voltage, current and its own temperature.
The LTC2943 includes a 14-bit No Latency ΔΣ analog-to-
digital converter, with internal clock and voltage reference
circuits.
The ADC can be used to monitor the battery voltage at
–
A precision analog coulomb counter integrates current
through a sense resistor between the battery’s positive
terminal and the load or charger. Battery voltage, battery
current and silicon temperature are measured with an
internal ADC.
SENSE or the battery current flowing through the sense
resistor or to convert the output of the on-chip tempera-
ture sensor.
Conversion of voltage, current and temperature are trig-
2
gered by programming the control register via the I C
interface. The LTC2943 includes a scan mode where
voltage, current and temperature conversion measure-
ments are executed every 10 seconds. At the end of each
conversion the corresponding registers are updated and
the converter goes to sleep to minimize quiescent current.
Coulomb Counter
Charge is the time integral of current. The LTC2943 mea-
sures charge by monitoring the voltage developed across
+
a sense resistor. The differential voltage between SENSE
–
andSENSE isappliedtoanauto-zeroeddifferentialanalog
The temperature sensor generates a voltage proportional
to temperature with a slope of 2mV/K resulting in a volt-
age of 600mV at 27°C.
integrator to infer charge.
When the integrator output ramps to REFHI or REFLO
levels, switches S1, S2, S3 and S4 toggle to reverse the
ramp direction (Figure 2). By observing the condition of
theswitchesandtherampdirection,polarityisdetermined.
Thisapproachalsosignificantlylowerstheimpactonoffset
of the analog integrator as described in the Differential
Offset Voltage section.
Power-Up Sequence
+
When SENSE rises above a threshold of approximately
3.3V, the LTC2943 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 while
the voltage, current and temperature ADC is switched
off. The accumulated charge register is set to mid-scale
(7FFFh), alllowthresholdregistersaresetto0000handall
high threshold registers are set to FFFFh. The alert mode
is enabled and the coulomb counter prescaling factor M
is set to 4096.
Aprogrammableprescalereffectivelyincreasesintegration
time by a factor M programmable from 1 to 4096. At each
underflow or overflow of the prescaler, the accumulated
chargeregister(ACR)valueisincrementedordecremented
one count. The value of accumulated charge is read via
2
the I C interface.
CHARGER
LOAD
REFHI
+
V
CC
CONTROL
LOGIC
+
–
SENSE
S1
S2
1
–
–
+
M
ACR
R
SENSE
PRESCALER
S3
S4
+
–
SENSE
8
2
POLARITY
DETECTION
I
BAT
REFLO
+
BATTERY
GND
2943 F02
Figure 2. Coulomb Counter Section of the LTC2943
2943fa
8
For more information www.linear.com/LTC2943
Linear [ Linear ]
