Applications Information; Hardware Configuration; Hw Config: Input Voltage Sensing And Modulation; Hw Config: Vinr Pin Connections - Analog Devices LINEAR LT8491 Manual

APPLICATIONS INFORMATION

HARDWARE CONFIGURATION

HW Config: Input Voltage Sensing and Modulation

The passive component network shown in Figure 11 is
required to modulate the solar panel voltage. It is also
used to measure the V
IN
power supply. This network is required whether the sup-
ply is a solar panel or a DC voltage source.
V
IN
R
FBIN1
R
DACI2
R
FBIN2
Figure 11. Input Feedback Resistor Network
Choosing the component values requires knowing the
maximum panel open-circuit voltage (V
the maximum DC input supply voltage (V
(see the HW Config: DC Supply Powered Charging sec-
tion). V typically occurs at cold temperatures and
OCMAX
should be specified in the panel manufacturer's data
sheet. Use the following equations to determine the
proper component values:
⎡
⎛
1+
⎢
⎝ ⎜
V
⎢
= 100k •
R
FBIN1
⎢
⎛
1+
⎢
⎝ ⎜
V
⎣
⎛
R
FBIN1
R = 2.75 •
⎝ ⎜
DACI2
V
MAX
R =
FBIN2
⎛
1
⎝ ⎜
100k –R
FBIN1
= 0.2 •R Ω
R
DACI1 DACI2
1
C =
DACI
1000 •R
DACI1
voltage when powered by a DC
LT8491
V
IN
FBIR
FBIN
R
DACI1
FBIW
C
DACI
GND
8491 F11
) as well as
OCMAX
) desired
DCMAX
⎤
⎞
4.470V
⎥
⎠ ⎟
– 6V
⎥
MAX
Ω
⎥
⎞
5.593
⎥
⎠ ⎟
– 6V
⎦
MAX
⎞
Ω
⎠ ⎟
– 6V
1
Ω
⎛ ⎞
⎞
1
–
⎠ ⎟ ⎝ ⎜ ⎠ ⎟
R
DACI2
F
For more information
where V is the greater of V
MAX
some additional margin. The resistors should have a 1%
tolerance or better.
Due to the granularity of standard resistor values, simply
rounding the calculated results to their nearest standard
values may result in unwanted errors. Consider using
multiple resistors in series to match the calculated results.
Otherwise, use standard resistor values and check the
final component selections with the following equations.
⎡
R
FBIN1
= 1.205 •
V
⎢
X2
R
⎣
DACI1
V indicates the actual V
X2
selected resistors. Make sure this result is greater than or
equal to the desired V
MAX
⎛
= V
V – 3.3 •
⎝ ⎜
X1 X2
R
DAC1
V should be as close to 6V as possible. Iterations may
X1
be required to determine the best standard resistor values.
Table 22 shows good sets of standard value components
for maximum input voltages (V
80V. Iterative calculations were required to select these
values that achieve the best overall results.
Table 22. Input Feedback Network vs V
V R R
MAX FBIN1 FBIN2
(V) (kΩ) (kΩ)
20 95.3 8.45
40 107 4.87
60 105 3.24
80 133 3.09
As discussed later in HW Config: DC Supply Powered
Charging, arbitrarily setting V
in the best operation of the LT8491 for all conditions,
particularly at low input voltages. Be sure to consider the
required voltage range for each application.

HW Config: VINR Pin Connections

The VINR pin is used for two functions. First, while the
LT8491 is powered by a solar panel, the VINR pin is
www.analog.com
LT8491
and V
OCMAX DCMAX
⎤
⎛ ⎞
R
FBIN1
+ +1
⎥
⎝ ⎜ ⎠ ⎟
+R R
⎦
DACI2 FBIN2
resulting from the use of the
MAX
for the application.
⎞
R
FBIN1
⎠ ⎟
+R
DAC2
) of 20V, 40V, 60V and
MAX
MAX
R R
DACI1 DACI2
(kΩ) (kΩ)
3.4 19.1
1.69 8.66
1.05 5.36
1.05 4.87
to 80V may not result
MAX
61
with
C
DACI
(nF)
270
560
1000
1000
Rev. 0