ltm8062 Linear Technology Corporation, ltm8062 Datasheet - Page 12

• Manufacturer Part Number: ltm8062
• Description: Ltm8062 32vin, 2a ?module Power Tracking Battery Charger Features
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
LTM8062
For example, given a common 36-cell solar panel that has
the following specified characteristics:
As the temperature coefficient for V
of V
(TC) of –78mV/°C and the specified peak power voltage
(V
to calculate the appropriate resistor values for the tem-
perature compensation network in Figure 4. With R
equal to 1k, 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.
12
MP
Open Circuit Voltage (V
Maximum Power Voltage (V
Open-Circuit Voltage Temperature Coefficient (V
= –78mV/°C
R
R
R
LTM8062
OC
SET
IN1
IN2
(25°C)) of 17.6V can be inserted into the equations
, the specified temperature coefficient for V
= −1k • (−0.078 • 4405) = 344k
=
= 1k
ADJ
BAT
17.6 + 344k • (0.0674 / 1k)
R
215k
FB3
R
210k
R
43k
FB1
FB2
2.7
Figure 5. Lead-Acid 6-Cell Float Charge Voltage vs Temperature with a –19.8mV/°C
Temperature Coefficient Using LM234 with the Feedback Network
344k
OC
R
2.4k
SET
) = 21.7V
MP
) = 17.6V
R
MP
V
V
− 1
+
–
is similar to that
LINEAR
TECHNOLOGY
LM234
= 24.4k
OC
+
)
SET
6-CELL
LEAD-ACID
BATTERY
OC
8062 F05a
In a manner similar to the MPPT temperature correction
outlined previously, implementation of linear battery charge
voltage temperature compensation can be accomplished by
incorporating a Linear Technology 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 5, with the desired temperature
coefficient (TC) and 25°C float voltage (V
specified, and using a convenient value of 2.4k for R
necessary resistor values follow the relations:
(see the Battery Float Voltage Programming section)
While the circuit in Figure 5 creates a linear tempera-
ture characteristic that follows a typical –3.3mV/°C per
cell lead-acid specification, the theoretical float charge
R
R
R
FB1
FB3
FB2
= 250k – R
=
= 43k
= –R
= –2.4k • (–0.0198 • 4405) = 210k
= 250k – 210k||43k = 215k
=
14.3
14.2
14.0
13.8
13.6
13.4
13.2
13.0
12.8
12.6
13.5 + 210k • (0.0674 / 2.4k)
V
FLOAT
–10
SET
• (TC • 4405)
0
(25°C) + R
FB1
10
||R
TEMPERATURE (°C)
3.3
210k
FB2
20
V
FB1
–19.8mV/°C
R
FB
30
FB1
• (0.0674 / R
40
50
8062 F05b
− 1
60
FLOAT
SET
)
(25°C))
− 1
SET
8062f
,