Datasheet

LTC4000-1
25
40001fa
For more information www.linear.com/LTC4001-1
In this configuration use the following formula to determine
the values of the three resistors:
R
VM3
= 1
1.193V
V
VM _RST
V
IN_REG
1V
R
IFB2
R
VM4
= 1.193
V
IN_REG
V
VM _RST
1
R
IFB2
Note that for the R
VM4
value to be positive, the ratio of
V
IN_REG
to V
VM_RST
has to be greater than 0.838.
When the RST pin of the LTC4000-1 is connected to the
SHDN or RUN pin of the converter, it is recommended that
the value of V
IN_REG
is set higher than the V
VM_RST
pin by a
significant margin. This is to ensure that any voltage noise
or ripple on the input supply pin does not cause the RST
pin to shut down the converter prematurely, preventing
the input regulation loop from functioning as expected.
As discussed in the input current monitoring section,
noise issues on the input node can be reduced by placing
a large filter capacitor on the CLN node (C
CLN
). To further
reduce the effect of any noise on the monitoring function,
another filter capacitor placed on the VM pin (C
VM
) is
recommended.
MPPT Temperature Compensation – Solar Panel
Example
The input regulation loop of the LTC4000-1 allows a user to
program a minimum input supply voltage regulation level
allowing for high impedance source to provide maximum
available power. With typical high
impedance source
such
as a solar panel, this maximum power point varies with
temperature.
A typical solar panel is comprised of a number of series-
connected cells, each cell being a forward-biased p-n
junction. As such, the open-circuit voltage (V
OC
) of a
solar cell has a temperature coefficient that is similar to
a common p-n junction diode, about –2mV/°C. The peak
power point voltage (V
MP
) for a crystalline solar panel
can be approximated as a fixed percentage of V
OC
, so the
temperature coefficient for the peak power point is similar
to that of V
OC
.
Panel manufacturers typically specify the 25°C values for
V
OC
, V
MP
and the temperature coefficient for V
OC
, making
determination of the temperature coefficient for V
MP
of a
typical panel straight forward.
applicaTions inForMaTion
IN
CC
1V
ITH
LTC4000-1
IN CLN RST
R
IS
DC/DC INPUT
TO DC/DC EN PIN
C
CLN
(OPTIONAL)
C
VM
IFB
VM
C
IN
+
+
C
C
TO DC/DC
COMPENSATION
PIN
40001 F16
R
C
A4
R
IFB2
R
VM4
R
VM3
CP1
+
1.193V
Figure 16. Input Voltage Monitoring and Input Voltage
Regulation Resistor Divider Combined
Figure 17. Temperature Characteristic of a Solar
Panel Open Circuit and Peak Power Point Voltages
TEMPERATURE (°C)
5
PANEL VOLTAGE
V
OC(25°C)
V
OC
– V
MP
V
MP(25°C)
4525
40001 F17
553515
V
MP
V
OC
V
OC
TEMP CO.
In a manner similar to the battery float voltage temperature
compensation, implementation of the MPPT temperature
compensation can be accomplished by incorporating an
LM234 into the input voltage feedback network. Using the