lt3652hv Linear Technology Corporation, lt3652hv Datasheet - Page 16

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

LT3652HV
APPLICATIONS INFORMATION
power tracking (MPPT) application. As the temperature
characteristic for a typical solar panel V
linear, a simple solution for tracking that characteristic can
be implemented using an LM234 3-terminal temperature
sensor. This creates an easily programmable, linear tem-
perature 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
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:
16
IN2
IN1
MP(25°C)
R
R
R
= 24.4k
Figure 8. MPPT Temperature Compensation Network
SET
IN1
IN2
= R
OC
= –R
, the specified temperature coefficient for V
IN1
= –1k • (–0.078 • 4405 ) = 344k
= 1k
= 344k/({[17.6 + 344k • (0.0674/1k)]/2.7} – 1)
V
SET
/({[V
MP(25°C)
) of 17.6V can be inserted into the equations to
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
) = 17.6V
SET
V
LT3652HV
IN_REG
MP
MP
V
IN
SET
3658 F08
is similar to that
voltage is highly
)]/V
IN_REG
SET
OC
) =
equal
} – 1)
OC
Figure 9. Lead-Acid 6-Cell Float Charge Voltage vs
Temperature Has –19.8mV/°C Characteristic Using LM234 with
Feedback Network
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,
or –19.8mV/°C. Using the feedback network shown in
Figure 9, with the desired temperature coefficient (TC)
LT3652HV
14.3
14.2
14.0
13.8
13.6
13.4
13.2
13.0
12.8
12.6
–10
BAT
V
FB
0
215k
R
210k
R
FB3
FB1
10
TEMPERATURE (°C)
R
43k
R
2.4k
FB2
20
SET
–19.8mV/°C
30
LM234
R
LEAD-ACID
40
BATTERY
6-CELL
V
V
+
–
50
3652 F09b
3652 F09a
60
+
3652hvf