LTC4000-1 Datasheet, PDF (23/40 Pages) Linear Technology – High Voltage High Current Controller for Battery Charging with Maximum Power Point Control

Applications Information
14.4
14.2
14.0
13.8
13.6
13.4
13.2
13.0
12.8
12.6
–10 0
10 20 30 40
TEMPERATURE (°C)
50 60
40001 F11
Figure 11. Lead-Acid 6-Cell Float Charge Voltage vs
Temperature Using LM234 with the Feedback Network
BAT
LTC4000-1
R_BFB1
210k
BFB
R_BFB2
13.0k
FBG
R_SET
2.43k
LM234
V⁺
R
V^–
6-CELL
LEAD-ACID
BATTERY
LTC4000-1
(TC = –19.8mV/°C and V_{FLOAT(25°C)} = 13.5V) and R_SET =
2.43k into the equation, we obtained the following values:
R_BFB1 = 210k and R_BFB2 = 13.0k.
3-Step Charging for Lead-Acid Battery
The LTC4000-1 naturally lends itself to charging ap-
plications requiring a constant current step followed by
constant voltage. Furthermore, the LTC4000-1 additional
features such as trickle charging, bad battery detection
and C/X or timer termination makes it an excellent fit for
Lithium based battery charging applications. Figure 13
and Table 2 show the normal steps involved in Lithium
battery charging.
TRICKLE CONSTANT
CHARGE CURRENT
CONSTANT VOLTAGE TERMINATION
BATTERY VOLTAGE
40001 F12
Figure 12. Battery Voltage Temperature Compensation Circuit
In the circuit shown in Figure 12,
R_BFB1 = –R_SET • (TC • 4405)
and
R_BFB2
=


V_{FLOAT(25°C)}
R_BFB1 • 1.136V
+
R_BFB1
•


0.0677
R_SET




–
1.136V
Where: TC = temperature coefficient in V/°C and V_{FLOAT(25°C)}
is the desired battery float voltage at 25°C in V.
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 coeffi-
cient or –19.8mV/°C. Substituting these two parameters
CHARGE
CURRENT
CHARGE TIME
40001 F13
Figure 13. Li-Ion Typical Charging Cycle
Table 2. Lithium Based Battery Charging Steps
STEP
CHARGE METHOD DURATION
Trickle Charge
Constant Current at a
Lower Current Value,
Usually 1/10th of Full
Charge Current
Until Battery Voltage Rises
Above Low Battery Threshold
Time Limit Set at TMR Pin
Constant Current Constant Current at Until Battery Voltage Reaches
Full Charge Current Float Voltage
No Time Limit
Constant Voltage Constant Voltage
Terminate Either When
Charge Current Falls to the
Programmed Level at the CX
Pin or after the Termination
Timer at TMR Pin Expires
Recharge
Initiate Constant
Current Again When
Battery Voltage Drops
Below Recharge
Threshold
40001f
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