LT3652 LINER [Linear Technology], LT3652 Datasheet - Page 17

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

APPLICATIONS INFORMATION
simple solution for tracking that characteristic can be
implemented using an LM234 3-terminal temperature
sensor. This creates an easily programmable, linear
temperature dependent characteristic.
In the circuit shown in figure 8,
R
R
Where: TC = temperature coefficient (in V/°C), and
For example, given a common 36-cell solar panel that has
the following specified characteristics:
Open Circuit Voltage (V
Maximum Power Voltage (V
Open-Circuit Voltage Temperature Coefficient (V
–78mV/°C
IN2
IN1
Figure 8. MPPT Temperature Compensation Network
= R
= –R
IN1
V
SET
/({[V
MP(25°C)
V
IN
• (TC • 4405), and
R
R
MP(25°C)
IN1
IN2
= maximum power voltage at 25°C
V
V
+
–
+ R
OC
LM234
R
IN1
) = 21.7V
MP
• (0.0674/R
R
SET
) = 17.6V
V
IN_REG
LT3652
V
IN
SET
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)]/V
IN_REG
OC
) =
} – 1)
As the temperature coefficient for V
of V
(TC) of –78mV/°C and the specified peak power voltage
(V
calculate the appropriate resistor values for the tempera-
ture compensation network in Figure 8. With R
to 1000Ω, then:
Battery Voltage Temperature Compensation
Some battery chemistries have charge voltage require-
ments that vary with temperature. Lead-acid batteries in
particular experience a significant change in charge volt-
age requirements as temperature changes. For example,
manufacturers of large lead-acid batteries recommend
a float charge of 2.25V/cell at 25°C. This battery float
voltage, however, has a temperature coefficient which is
typically specified at –3.3mV/°C per cell.
In a manner similar to the MPPT temperature correction
outlined previously, implementation of linear battery
charge voltage temperature compensation can be ac-
complished by incorporating an LM234 into the output
feedback network.
For example, a 6-cell lead acid battery has a float charge
voltage that is commonly specified at 2.25V/cell at 25°C,
or 13.5V, and a –3.3mV/°C per cell temperature coefficient,
MP(25°C)
R
R
R
= 24.4k
IN2
SET
IN1
OC
, the specified temperature coefficient for V
= –1k • (–0.078 • 4405 ) = 344k
= 1k
= 344k/({[17.6 + 344k • (0.0674/1k)]/2.7} – 1)
) of 17.6V can be inserted into the equations to
MP
is similar to that
LT3652
SET
17
equal
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OC