Figure 1. 2-Wire Bus Timing Diagram
Detailed Description
Figure 1 shows the 2-wire bus timing diagram, and
Figure 2 is the MAX17043/MAX17044 block diagram.
ModelGauge Theory of Operation
The MAX17043/MAX17044 use a sophisticated battery
model that determines the SOC of a nonlinear Li+
battery. The model effectively simulates the internal
dynamics of a Li+ battery and determines the SOC. The
model considers the time effects of a battery caused by
the chemical reactions and impedance in the battery.
The MAX17043/MAX17044 SOC calculation does not
accumulate error with time. This is advantageous
compared to traditional coulomb counters, which suffer
from SOC drift caused by current-sense offset and cell
self-discharge. This model provides good performance
for many Li+ chemistry variants across temperature
and age. To achieve optimum performance, the
MAX17043/MAX17044 must be programmed with con-
figuration data custom to the application. Contact the
factory for details.
Fuel-Gauge Performance
The classical coulomb-counter-based fuel gauges suf-
fer from accuracy drift due to the accumulation of the
offset error in the current-sense measurement. Although
the error is often very small, the error increases over
time in such systems, cannot be eliminated, and
requires periodic corrections. The corrections are usu-
ally performed on a predefined SOC level near full or
empty. Some other systems use the relaxed battery
voltage to perform corrections. These systems deter-
mine the true SOC based on the battery voltage after a
long time of no activity. Both have the same limitation: if
the correction condition is not observed over time in the
actual application, the error in the system is boundless.
In some systems, a full-charge/discharge cycle is
required to eliminate the drift error. To determine the
true accuracy of a fuel gauge, as experienced by end
users, the battery should be exercised in a dynamic
manner. The end-user accuracy cannot be understood
with only simple cycles. MAX17043/MAX17044 do not
suffer from the drift problem since they do not rely on
the current information.
