Maximum Power Point Tracking; Telemetry Operation - Analog Devices LINEAR LT8491 Manual

OPERATION
Any active fault causes the charging to stop, the stage
timers to pause their countdown, and the status to be
reported as follows:
• STAT_CHARGER→CHRG_FAULT=1, indicating the
presence of a fault.
• STAT_CHARGER→CHRG_STAGE holds its last value.
• STAT_CHRG_FAULTS indicates the source of the fault.
• STAT_SUPPLY→SOLAR_STATE=000b.
• STATUS pin indication. See Table 25.
After a fault is detected, the LT8491 typically continues to
monitor for the presence of faults and, when no faults are
present, the charging resumes or restarts. However, this
behavior depends on the CFG_RSTRT_IN_FLT register
settings discussed in the Configure Automatic Restart
section and below. Telemetry acquisition generally contin-
ues during a fault although some telemetry, related to the
battery side of the charger, may be limited as discussed
in the Telemetry: Acquisition section.
Faults are monitored on a priority basis as follows:
• Battery Disconnect Fault: (BAT_DISCON_FLT=1) The
presence of a battery disconnect fault, as measured
at the TEMPSENSE pin, inhibits checking for all faults
except this one. As such, the low V
perature faults are cleared. If CFG_RSTRT_IN_FLT→
NO_RSTRT_ON_DISCON_FLT=1 then the detection of
this fault stops the LT8491 from checking the status of
all faults and the charging won't restart until it's reset
or cycled off-then-on via the CHRG_EN control bit.
• TBAT Battery Temperature Fault: (LOW_TBAT_FLT
or HIGH_TBAT_FLT=1) During a T
VBAT_FLT bit is not updated. If CFG_RSTRT_IN_
FLT→NO_RESUME_ON_TBAT_FLT=1 then the charg-
ing won't resume until the charger is reset or cycled
off-then-on via the CHRG_EN control bit.
• Stage Timer Expired Fault: (TSx_EXPIRED_FLT=1)
During a stage timer fault, if CFG_RSTRT_IN_FLT→
NO_RSTRT_ON_VOLTS=0 and there is no battery
disconnect or T fault, the LT8491 measures V
BAT
every 5 seconds to check if an automatic restart can be
• V

MAXIMUM POWER POINT TRACKING

When powered by a solar panel, the LT8491 employs a
proprietary Perturb and Observe algorithm for identify-
ing the maximum power point. This algorithm provides
accurate MPPT for slow to moderate changes in panel
illumination. The panel is also fully scanned periodically
and V tem-
to avoid settling on a false maximum power point for long
BAT BAT
periods of time, in the case of non-uniform panel illumi-
nation. The frequency of performing full panel scans can
be configured in the CFG_SCAN_RATE and CFG_SCAN_
RATE_LP registers.

TELEMETRY OPERATION

fault the LOW_
BAT
The LT8491 generates digital telemetry including battery
temperature, input and output current, input and output
voltage, power and efficiency. The latest measurement
results are stored in the read-only telemetry registers
summarized in the I
word-sized values must be read using the I
transaction to avoid retrieving mismatched bytes (see I
Data Transfer Transactions)
BAT
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initiated. The TELE_VBAT register and the LOW_VBAT_
FLT bit are updated with each new V
During a stage timer fault, if CFG_RSTRT_IN_
FLT→NO_RSTRT_ON_VOLTS=1, then the charging
will not restart until the charger (1) is reset or (2) is
cycled off-then-on via the CHRG_EN control bit, or
(3) automatically restarts due to the CFG_RSTRT_IN_
FLT→RSTRT_ON_TMR_FLT_HRS settings. In addi-
tion, the LOW_VBAT_FLT bit is not updated until the
charging restarts.
Low Fault: (LOW_VBAT_FLT=1) When LOW_
BAT
VBAT_FLT is the only fault present, V
once per second to check for higher voltage to restart
the charger. However, if CFG_RSTRT_IN_FLT→ NO_
RSTRT_ON_BATLOW_FLT=1 then the charging and
V measurements stop until the charger is reset or
BAT
cycled off-then-on via the CHRG_EN control bit.
2
C Register Map and in Table 9. These
LT8491
measurement.
BAT
is measured
BAT
2
C word-read
2
C:
Rev. 0
23