MAX17058_13 Datasheet, PDF (9/16 Pages) Maxim Integrated Products – 1-Cell/2-Cell Li+ ModelGauge ICs

MAX17058/MAX17059
1-Cell /2-Cell Li+ ModelGauge ICs
Battery-Swap Detection
If V_CELL falls below V_RST then returns above V_RST, the IC
quick-starts. This handles the battery swap; the SOC of
the previous battery doesn not affect that of the new one.
See the Quick-Start and VRESET Register (0x18) sections.
Quick-Start
If the IC generates an erroneous initial SOC, the bat-
tery insertion and system power-up waveforms must
be examined to determine if a quick-start is necessary,
as well as the best time to execute the command. The
IC samples the maximum V_CELL during the first 17ms
(see the Battery Insertion section). Unless V_CELL is fully
relaxed, even the best sampled voltage can appear
greater or less than OCV. Therefore, quick-start must be
used cautiously.
Most systems should not use quick-start because the
ICs handle most startup problems transparently, such
as intermittent battery-terminal connection during inser-
tion. If battery voltage stabilizes faster than 17ms, as
illustrated in Figure 6, then do not use quick-start.
The quick-start command restarts fuel-gauge calcula-
tions in the same manner as initial power-up of the IC.
If the system power-up sequence is so noisy that the initial
estimate of SOC has unacceptable error, the system
microcontroller might be able to reduce the error by
using quick-start. A quick-start is initiated by a rising
edge on the QSTRT pin, or by writing 1 to the quick-start
bit on the MODE register.
Figure 7 illustrates a waveform that could corrupt the
initial SOC. If the disturbance is severe, quick-start after
the inrush current has stopped and voltage has settled,
but before the system is fully powered. If issued too soon
or too late, a quick-start causes SOC error.
Large inrush current might reduce V_CELL longer than the
initial sampling period. Issue a quick-start so that V_CELL
is nearest OCV during the 17ms following the command.
If the IC remains powered by a charger when the cell is
removed, then it continues to measure the charge volt-
age even though the cell is not present. When the cell is
reinserted, quick-start before the charger affects V_CELL.
Power-On Reset (POR)
POR includes a quick-start, so only use it for when
a quick-start is safe (see the Quick-Start section).
This command restores all registers to their default
values. After this command, reload the custom model.
See the CMD Register (0xFE) section.
Alert Interrupt
The ICs can interrupt a system microcontroller when
SOC becomes low. See the CONFIG Register (0x0C)
and STATUS Register (0x1A) sections. When the alert is
triggered, the IC asserts the ALRT pin logic-low and sets
CONFIG.ALRT = 1. The ALRT pin remains logic-low until
the system writes CONFIG.ALRT = 0 to clear the alert.
The alert function is enabled by default and can occur
immediately upon power-up. Entering sleep mode does
not clear the ALRT bit or the ALRT pin.
VCELL
STEADY SYSTEM
LOAD BEGINS
17ms
TIME
VCELL HAS FULLY RELAXED
INITIAL SAMPLE DEBOUNCE WINDOW
Figure 6. Insertion Waveform Not Requiring Quick-Start
Command
Maxim Integrated
V_CELL
17ms
INITIAL SAMPLE
DEBOUNCE WINDOW
BEST TIME TO
QUICK-START
VCELL HAS
FULLY RELAXED
QUICK-START DURING
THIS TIME SPAN
STEADY SYSTEM
LOAD BEGINS
TIME
Figure 7. Insertion Waveform Requiring Quick-Start Command
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