LTC4000-1 Datasheet, PDF (18/40 Pages) Linear Technology – High Voltage High Current Controller for Battery Charging with Maximum Power Point Control

LTC4000-1
Applications Information
a capacitor is connected to the CSP pin (C_CSP). This is to
reduce the AC content of the current through the sense
resistor (R_CS). Where the highest accuracy is important,
pick the value of C_CSP such that the AC content is less
than or equal to 50% of the average voltage across the
sense resistor. Similar to the IIMON pin, the voltage on the
IBMON pin is filtered further by putting a capacitor on the
pin (C_IBMON). This filter capacitor should not be arbitrarily
large as it will slow down the overall compensated charge
current regulation loop. For details on the loop compensa-
tion, refer to the Compensation section.
Battery Float Voltage Programming
When the value of R_BFB1 is much larger than 100Ω, the final
float voltage is determined using the following formula:
R_BFB1
=


V_FLOAT
1.136V
–
1^{}
R_BFB2
When higher accuracy is important, a slightly more ac-
curate final float voltage can be determined using the
following formula:
V_FLOAT
=


R_BFB1 +R_BFB2
R_BFB2
• 1.136V ^{}
–


R_BFB1
R_BFB2
•
V_FBG


where V_FBG is the voltage at the FBG pin during float
voltage regulation, which accounts for all the current
from all resistor dividers that are connected to this pin
(R_FBG = 100Ω typical).
Low Battery Trickle Charge Programming and Bad
Battery Detection
When charging into an over-discharged or dead battery
(V_BFB < V_LOBAT), the pull-up current at the CL pin is reduced
to 10% of the normal pull-up current. Therefore, the trickle
charge current is set using the following formula:
R_CL
=
I_CLIM(TRKL) • R_CS
0.25µA
⇒ I_CLIM(TRKL)
=
0.25µA
•
R_CL
R_CS
Therefore, when 50µA•R_CL is less than 1V, the following
relation is true:
I_{CLIM( TRKL )}
=
I_CLIM
10
Once the battery voltage rises above the low battery voltage
threshold, the charge current level rises from the trickle
charge current level to the full charge current level.
The LTC4000-1 also features bad battery detection. This
detection is disabled if the TMR pin is grounded or tied
to BIAS. However, when a capacitor is connected to the
TMR pin, a bad battery detection timer is started as soon
as trickle charging starts. If at the end of the bad battery
detection time the battery voltage is still lower than the
low battery threshold, charging is terminated and the part
indicates a bad battery condition by pulling the FLT pin low
and leaving the CHRG pin high impedance.
The bad battery detection time can be programmed ac-
cording to the following formula:
C_TMR(nF) = t_BADBAT(h) • 138.5
Note that once a bad battery condition is detected, the
condition is latched. In order to re-enable charging, re-
move the battery and connect a new battery whose voltage
causes BFB to rise above the recharge battery threshold
(V_RECHRG(RISE)). Alternatively toggle the ENC pin or remove
and reapply power to IN.
C/X Detection, Charge Termination and Automatic
Recharge
Once the constant voltage charging is reached, there are
two ways in which charging can terminate. If the TMR pin
is tied to BIAS, the battery charger terminates as soon as
the charge current drops to the level programmed by the
CX pin. The C/X current termination level is programmed
according to the following formula:
R_CX
=
I_{C/ X} • R_CS
0.25µA
+
0.5mV
⇒
I_C/X
=
(^0.25µA
• R_CX
R_CS
)
−
0.5mV
40001f
18