LT3652 LINER [Linear Technology], LT3652 Datasheet - Page 16

• Manufacturer Part Number: LT3652
• Description: Power Tracking 2A Battery Charger for Solar Power
• Manufacturer: LINER [Linear Technology]

LT3652
APPLICATIONS INFORMATION
cleaning measures should be implemented to prevent
board contamination, and low-leakage solder flux is
recommended.
Input Supply Voltage Regulation
The LT3652 contains a voltage monitor pin that enables
programming a minimum operational voltage. Connect-
ing a resistor divider from V
programming of minimum input supply voltage, typically
used to program the peak power voltage for a solar panel.
Maximum charge current is reduced when the V
is below the regulation threshold of 2.7V.
If an input supply cannot provide enough power to satisfy
the requirements of an LT3652 charger, the supply voltage
will collapse. A minimum operating supply voltage can
thus be programmed by monitoring the supply through
a resistor divider, such that the desired minimum volt-
age corresponds to 2.7V at the V
servos the maximum output charge current to maintain
the voltage on V
Programming of the desired minimum voltage is ac-
complished by connecting a resistor divider as shown in
Figure 6. The ratio of R
voltage (V
If the voltage regulation feature is not used, connect the
V
16
IN_REG
R
IN1
/R
pin to V
Figure 6. Resistor Divider Sets Minimum V
IN2
IN(MIN)
SUPPLY
= (V
INPUT
IN
IN_REG
) is:
IN(MIN)
.
at or above 2.7V.
R
R
/2.7) – 1
IN1
IN1
IN2
/R
IN
IN2
to the V
for a desired minimum
IN_REG
V
V
IN_REG
IN
LT3652
IN_REG
3652 F06
pin. The LT3652
pin enables
IN
IN_REG
pin
MPPT Temperature Compensation
A typical solar panel is comprised of a number of series-con-
nected cells, each cell being a forward-biased p-n junction.
As such, the open-circuit voltage (V
a temperature coefficient that is similar to a common p-n
diode, or about –2mV/°C. The peak power point voltage
(V
a fixed voltage below V
for the peak power point is similar to that of V
Panel manufacturers typically specify the 25°C values for
V
determination of the temperature coefficient for V
typical panel straight forward.
The LT3652 employs a feedback network to program the
V
makes for efficient implementation of various temperature
compensation schemes for a maximum peak power track-
ing (MPPT) application. As the temperature characteristic
for a typical solar panel V
OC
IN
MP
, V
input regulation voltage. Manipulation of the network
Figure 7. Temperature Characteristics for Solar Panel
Output Voltage
) for a crystalline solar panel can be approximated as
MP
V
V
MP(25°C)
OC(25°C)
, and the temperature coefficient for V
5
15
TEMPERATURE (°C)
V
OC
MP
25
, so the temperature coefficient
MP
V
OC
voltage is highly linear, a
TEMP CO.
35
V
OC
OC
45
) of a solar cell has
3652 F07
55
OC
V
OC
OC
, making
.
– V
MP
MP
3652fb
of a