LT3652 LINER [Linear Technology], LT3652 Datasheet - Page 18

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

LT3652
APPLICATIONS INFORMATION
or –19.8mV/°C. Using the feedback network shown in
Figure 9, with the desired temperature coefficient (TC)
and 25°C float voltage (V
a convenient value of 2.4k for R
values follow the relations:
R
R
R
Figure 9. Lead-Acid 6-Cell Float Charge Voltage vs
Temperature Has –19.8mV/°C Characteristic Using LM234 with
Feedback Network
18
FB1
FB2
FB3
= –R
= –2.4k • (–0.0198 • 4405) = 210k
= R
= 210k/({[13.5 + 210k • (0.0674/2.4k)]/3.3} – 1)
= 43k
= 250k - R
= 250k – 210k||43k = 215k (see the Battery Float
Voltage Programming section)
LT3652
R
14.3
14.2
14.0
13.8
13.6
13.4
13.2
13.0
12.8
12.6
FB1
SET
–10
SET
BAT
V
FB
)] / V
/ ({[V
• (TC • 4405)
0
R
215k
FB1
210k
R
FB3
FB
FB1
FLOAT(25°C)
||R
10
} – 1)
TEMPERATURE (°C)
FB2
R
43k
R
2.4k
FLOAT(25°C)
FB2
20
SET
–19.8mV/°C
30
+ R
LM234
SET
R
LEAD-ACID
40
FB1
BATTERY
) specified, and using
6-CELL
, necessary resistor
V
V
+
–
50
• (0.0674/
3652 F09b
3652 F09a
60
+
Figure 10. Thermistor-Based Temperature Compensation
Network Programs V
Float Charge Voltage for 6-Cell Charger
While the circuit in Figure 9 creates a linear temperature
characteristic that follows a typical –3.3mV/°C per cell
lead-acid specification, the theoretical float charge voltage
characteristic is slightly nonlinear. This nonlinear charac-
teristic follows the relation V
– 6 × 10
T = temperature in °C. A thermistor-based network can
be used to approximate the nonlinear ideal temperature
characteristic across a reasonable operating range, as
shown in Figure 10.
–3
14.8
14.6
14.4
14.2
14.0
13.8
13.6
13.4
13.2
13.0
12.8
(T) + 2.375 (with a 2.18V minimum), where
LT3652
–10
BAT
V
PROGRAMMED V
FB
0
FLOAT
198k
196k
69k
69k
10
TEMPERATURE (°C)
to Closely Match Ideal Lead-Acid
20
BAT(FLOAT)
THEORETICAL V
FLOAT(1-CELL)
30
22k
B = 3380
LEAD-ACID
BATTERY
40
6-CELL
FLOAT
50
3652 F10a
3652 F10b
+
= 4 × 10
60
–5
(T
3652fb
2
)