lt3652hv Linear Technology Corporation, lt3652hv Datasheet - Page 15

• Manufacturer Part Number: lt3652hv
• Description: Lt3652hv Power Tracking 2a Battery Charger Features
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
Because the V
stray capacitances at this pin must be minimized. Special
attention should be given to any stray capacitances that
can couple external signals onto the pin, which can pro-
duce undesirable output transients or ripple. Effects of
parasitic capacitance can typically be reduced by adding
a small-value (20pF to 50pF) feedforward capacitor from
the BAT pin to the V
Extra care should be taken during board assembly. Small
amounts of board contamination can lead to significant
shifts in output voltage. Appropriate post-assembly board
cleaning measures should be implemented to prevent
board contamination, and low-leakage solder flux is
recommended.
Input Supply Voltage Regulation
The LT3652HV 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 LT3652HV charger, the supply volt-
age will collapse. A minimum operating supply voltage can
thus be programmed by monitoring the supply through
a resistor divider, such that the desired minimum voltage
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
To satisfy the 250k equivalent resistance to the V
pin:
R
IN1
R
R
/R
FB3
FB3
IN2
IN(MIN)
= 250k − 27.5k
= 223k.
= (V
FB
IN_REG
) is:
pin is a relatively high impedance node,
IN(MIN)
FB
pin.
at or above 2.7V.
/2.7) – 1
IN1
/R
IN
IN2
IN_REG
to the V
for a desired minimum
pin. The LT3652HV
IN_REG
pin enables
IN_REG
FB
pin
If the voltage regulation feature is not used, connect the
V
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 LT3652HV employs a feedback network to program
the V
network makes for efficient implementation of various
temperature compensation schemes for a maximum peak
IN_REG
OC
MP
, V
Figure 7. Temperature Characteristics for Solar Panel
Output Voltage
) for a crystalline solar panel can be approximated as
IN
MP
V
V
MP(25°C)
OC(25°C)
pin to V
input regulation voltage. Manipulation of the
, and the temperature coefficient for V
Figure 6. Resistor Divider Sets Minimum V
SUPPLY
5
INPUT
IN
.
15
TEMPERATURE (°C)
V
OC
MP
R
R
IN1
IN2
25
, so the temperature coefficient
V
OC
TEMP CO.
35
V
V
V
IN_REG
IN
OC
OC
LT3652HV
LT3652HV
45
) of a solar cell has
3652 F07
3652 F06
55
OC
V
OC
IN
OC
, making
.
– V
15
MP
MP
3652hvf
of a