Datasheet

LTC2941-1
7
29411f
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 I
2
C interface.
Power-Up Sequence
When V
SENSE
+
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.
–
+
–
+
–
+
+
S4
REFHI
REFLO
S3
S2
S1
LOADCHARGER
SENSE
+
R
SENSE
R
BOND
R
BOND
BATTERY
I
BAT
1
5
SENSE
–
6
GND
2
POLARITY
DETECTION
CONTROL
LOGIC
PRE-
SCALER
M
I
2
C/
SMBus
REGISTERS
AL/CC
3
SCL
4
SDA
29411 F03
STATUS
CONTROL
ACR
THRESHOLDS
V
SUPPLY
Figure 3. Coulomb Counter Section of the LTC2941-1