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APPLICATIONS INFORMATION
HW Config: Input Voltage Sensing and Modulation sec-
tion. Maximum charging current can reduce as FBIN
gets closer to its regulation voltage of 1.205V (typical).
This is not normally a significant issue unless 1) the
charger is powered by a low voltage DC power supply
or 2) a low voltage panel is used with a charger that is
configured for a much higher voltage panel. The far-
ther that V
is below the Normal Configuration line in
IN
Figure 13 the more the current can reduce.
When using a solar panel supply, choose a panel hav-
ing a maximum open-circuit voltage (V
to V
(discussed in the HW Config: Input Voltage
MAX
Sensing and Modulation section). The maximum power
point voltage is typically well above the voltage thresh-
olds in Figure 13 and current limiting is rarely an issue.
Avoid using solar panels that operate dramatically
below V
, particularly if the maximum power point
MAX
voltage is typically below the Normal Configuration line
in Figure 13.
25
20
NORMAL CONFIGURATION
15
10
5
DC SUPPLY ONLY WITH FBIN = LDO33
0
0
10
20
Figure 13. Minimum Full Charging Current V
Input Current Limiting: Review the solar section of the HW
Config: Input Current Sense and Limit section.
HW Config: DC Supply Powered Charging
There are a few special items to consider when the char-
ger is powered by a DC power supply as discussed in
these subsections below.
Selecting Power Supply Mode: Power supply mode
must be enabled when supplying the LT8491 by a DC
) close
OCMAX
30
40
50
60
70
80
V
(V)
MAX
8491 F13
Voltage
IN
For more information
voltage source. This is done by pulling the VINR pin low,
or to ground, as discussed in the HW Config: VINR Pin
Connections section. The Optional: DC Supply Detection
Section describes a method to pull VINR low automati-
cally when a DC supply is present.
Minimum Input Voltage Requirement: When in power sup-
ply mode, the LT8491 will operate from an input as low as
6V. However, charging current capability can become lim-
ited at low input voltages depending on the V
used when determining the input voltage sensing network
resistor values (see previous HW Config: Input Voltage
Sensing and Modulation section). Figure 13 shows the
minimum input supply voltage required, below which,
charging current can drop below the maximum output
current limit. If the LT8491 will only be powered by a DC
supply, the minimum input voltage shown in Figure 13
can be reduced to 6V by (1) disconnecting FBIN from
FBIR and (2) connecting the FBIN pin directly to LDO33.
Input Current Limiting: Input current limiting should be
considered when using DC power supplies. This is dis-
cussed later in the HW Config: Input Current Sense and
Limit section.
HW Config: V
in Stage 2 (V
BAT
The Stage 2 battery voltage (V
charging voltage. The voltage limits for Stages 0, 1 and
3 are configured as percentages of V
the Configure V
for Stages 0,1 and 3 section. If tem-
BAT
perature compensated charging is enabled, then V
change with temperature as discussed in the Configure
Temperature Compensation section. As such, the settings
for the other stages will also change with temperature in
proportion to V
.
S2
LT8491
FBOUT
FBOR
FBOW
GND
Figure 14. Output Feedback Resistor Network
www.analog.com
LT8491
voltage
MAX
)
S2
) is the maximum battery
S2
as discussed in
S2
S2
V
BAT
R
FBOUT1
R
R
DACO1
DACO2
R
C
FBOUT2
DACO
8491 F14
63
will
Rev. 0
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