LTC4000-1 Datasheet, PDF (24/40 Pages) Linear Technology – High Voltage High Current Controller for Battery Charging with Maximum Power Point Control

LTC4000-1
Applications Information
On the other hand, the LTC4000-1 is also easily configu-
rable to handle lead-acid based battery charging. One of
the common methods used in lead-acid battery charging
is called 3-step charging (Bulk, Absorption and Float).
Figure 14 and Table 3 summarize the normal steps involved
in a typical 3-step charging of a lead-acid battery.
BULK
CHARGE
BATTERY VOLTAGE
ABSORPTION
FLOAT
(STORAGE)
CHARGE
CURRENT
CHARGE TIME
40001 F14
Figure 14. Lead-Acid 3-Step Charging Cycle
Table 3. Lead-Acid Battery Charging Steps
STEP
CHARGE METHOD DURATION
Bulk Charge
Constant Current
Until Battery Voltage Reaches
Absorption Voltage
No Time Limit
Absorption
Constant Voltage
at the Absorption
Voltage Level
Terminate When Charge
Current Falls to the
Programmed Level at the CX
Pin
Float (Storage)
Constant Voltage
at the Lower Float
Voltage Level (Float
Voltage Is Lower
than the Absorption
Voltage)
Indefinite
Recharge
Initiate Bulk Charge
Again When Battery
Voltage Drops Below
Recharge Threshold
Figure 15 shows the configuration needed to implement
this 3-step lead-acid battery charging with the LTC4000-1.
LTC4000-1
CSP
CSN
BAT
FBG
R_BFB2
BFB
R_BFB3
CX CL ^CHRG
R_CX
R_CL
FROM DC/DC
OUTPUT
R_CS
R_BFB1
LEAD-ACID
BATTERY
40001 F15
Figure 15. 3-Step Lead-Acid Circuit Configuration
When a charging cycle is initiated, the CHRG pin is pulled
low. The charger first enters the bulk charge step, charg-
ing the battery with a constant current programmed at
the CL pin:
( ) _ICLIM
=
MIN
50mV, 2.5µA • R_CL
R_CS
When the battery voltage rises to the Absorption voltage
level:
( ) _VABSRP
=
 R_BFB1 R_BFB2 + R_BFB3

R_BFB2R_BFB3
+ 1^{} • 1.136V
the charger enters the Absorption step, charging the bat-
tery at a constant voltage at this absorption voltage level.
As the charge current drops to the C/X level:
( ) _{ICLIM =}
0.25µA • R_CX
R_CS
– 0.5mV
the CHRG pin turns high impedance and now the charger
enters the Float (Storage) step, charging the battery volt-
age at the constant float voltage level:
V_FLOAT
=
 R_BFB1
 R_BFB2
+ 1^{}
• 1.136V
40001f
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