Hw Config: Solar Panel Powered Charging - Analog Devices LINEAR LT8491 Manual

LT8491
APPLICATIONS INFORMATION
measured to determine the absolute panel voltage and
check for under voltage conditions. As such, VINR must
be connected to the resistor divider network shown in
Figure 12. These resistors should have a 1% tolerance
or better.
V
IN
196k
8.06k
Figure 12. VINR Resistor Divider Circuit
Second, the LT8491 enters power supply mode when
VINR is pulled low (<174mV typical). Power supply mode
disables unnecessary solar panel functions and allows the
LT8491 to operate properly from a DC voltage source.
The activation of power supply mode is indicated in the
STAT_SUPPLY and TELE_VINR registers.
If the charger is only going to be powered by a DC voltage
source, then the VINR pin can be grounded. If the charger
will only be powered by a solar panel, then connect VINR
as shown in Figure 12. If both supply methods may be
used, then see the Optional: DC Supply Detection Circuit
section for a method to pull down the VINR pin when a
DC supply is detected.

HW Config: Solar Panel Powered Charging

There are a few special items to consider when the char-
ger is powered by a solar panel as discussed in these
subsections below.
VINR Connection: The VINR pin must be connected as
shown in Figure 12 when being powered by a solar panel.
Timers Disabled: When powered by a solar panel, the
charging timers are disabled. Timer termination and timer
faults are also disabled regardless of their configura-
tion settings. See data sheet sections: Configure Stage
Timeout Limits and Configure Charge Termination.
62
LT8491
V
IN
VINR
GND
8491 F12
For more information
Timers are disabled when solar powered due to the
inability to guarantee full charging current during the
entire charging cycle when panel illumination conditions
change. In addition, the timers can reset if all power to
the charger is lost due to insufficient lighting. This makes
the use of timers potentially unreliable in solar powered
applications.
C/10 Detection: When powered by a solar panel, charg-
ing current may drop below C/10 either because (1) the
battery is approaching full charge or (2) insufficient panel
power is available. The LT8491 can determine which
condition has caused the current to drop. When con-
figured for a C/10 termination or stage transition (see
CFG_TERMINATE and CFG_CHRG_MISC registers) the
transition will only occur if C/10 is due to the battery
approaching full charge. Otherwise the C/10 or charging
termination transition will not occur. See Figure 8 for more
information about available C/10 state transitions.
Minimum Panel Voltage: A minimum panel voltage of 6V
is required to operate the charger. However higher panel
voltages are required in various other cases.
1. LOW POWER MODE ENABLED: Low power mode allows
additional power to be recovered from the solar panel
under very weak lighting conditions. When low power
mode is enabled (CFG_CHRG_MISC→LPMODE_
EN=1), the panel voltage must initially exceed 10V
(typical – as measured through the VINR pin) before
the charger will attempt to charge the battery. Read the
Optional: Low Power Mode section for more details.
2. LOW POWER MODE DISABLED: If low power mode
is disabled (CFG_CHRG_MISC→LPMODE_EN=0) the
charger will attempt to charge the battery if the panel
is above 6V. However, if sufficient panel current is not
detected, the LT8491 will temporarily stop charging.
The charger will check for sufficient panel current at
30 second intervals (typical) or will check sooner if the
LT8491 detects a significant rise in panel voltage or a
significant fall in battery voltage.
3. LOW INPUT VOLTAGE EFFECTS: Figure 13 shows the
minimum input voltage, below which the maximum
charging current may be reduced. This limit is a func-
tion of the input V
MAX
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as discussed previously in the
Rev. 0