Datasheet
LTC4000-1
22
40001fa
For more information www.linear.com/LTC4001-1
applicaTions inForMaTion
In the circuit shown in Figure 12,
R
BFB1
= –R
SET
•(TC • 4405)
and
R
BFB2
=
R
BFB1
• 1.136V
V
FLOAT(25°C)
+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
(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.
Figure 13. Li-Ion Typical Charging Cycle
CHARGE TIME
40001 F13
CONSTANT VOLTAGE
CONSTANT
CURRENT
TRICKLE
CHARGE
CHARGE
CURRENT
BATTERY VOLTAGE
TERMINATION
Figure 12. Battery Voltage Temperature Compensation Circuit
Figure 11. Lead-Acid 6-Cell Float Charge Voltage vs
Temperature Using LM234 with the Feedback Network
TEMPERATURE (°C)
–10
V
FLOAT
(V)
14.4
14.2
13.8
13.4
13.0
14.0
13.6
13.2
12.8
12.6
3010 50
40001 F11
60200 40
R
BFB1
210k
R
BFB2
13.0k
BFB
R
LM234
V
+
V
–
BAT
FBG
LTC4000-1
R
SET
2.43k
40001 F12
6-CELL
LEAD-ACID
BATTERY
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
Full Charge Current
Until Battery Voltage Reaches
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