LT3652HV
18
3652hvfb
For more information www.linear.com/LT3652HV
APPLICATIONS INFORMATION
of approximately 100mV appears at the charger output,
due to cycling between termination and recharge events,
This cycling results in pulsing at the CHRG output. An
LED connected to this pin will exhibit a blinking pattern,
indicating to the user that a battery is not present. The
frequency of this blinking pattern is dependent on the
output capacitance.
C/10 Termination
The LT3652HV supports a low-current based termination
scheme, where a battery charge cycle terminates when the
current output from the charger falls to below one-tenth
of the maximum current, as programmed with R
SENSE
.
The C/10 threshold current corresponds to 10mV across
R
SENSE
. This termination mode is engaged by shorting
the TIMER pin to ground.
When C/10 termination is used, a LT3652HV charger will
source battery charge current as long as the average current
level remains above the C/10 threshold. As the full-charge
float voltage is achieved, the charge current falls until
the C/10 threshold is reached, at which time the charger
terminates and the LT3652HV enters standby mode. The
CHRG status pin follows the charger cycle, and is high
impedance when the charger is not actively charging.
When V
BAT
drops below 97.5% of the full-charged float
voltage, whether by battery loading or replacement of the
battery, the charger automatically re-engages and starts
charging.
There is no provision for bad battery detection if C/10
termination is used.
Timer Termination
The LT3652HV supports a timer based termination scheme,
in which a battery charge cycle is terminated after a specific
amount of time elapses. Timer termination is engaged
when a capacitor (C
TIMER
) is connected from the TIMER
pin to ground. The timer cycle EOC (T
EOC
) occurs based
on C
TIMER
following the relation:
C
TIMER
= T
EOC
• 2.27 × 10
–7
(Hours)
Timer EOC is typically set to 3 hours, which requires a
0.68µF capacitor.
The CHRG status pin continues to signal charging at a C/10
rate, regardless of what termination scheme is used. When
timer termination is used, the CHRG status pin is pulled
low during a charging cycle until the charger output current
falls below the C/10 threshold. The charger continues to
top-off the battery until timer EOC, when the LT3652HV
terminates the charging cycle and enters standby mode.
Termination at the end of the timer cycle only occurs if
the charging cycle was successful. A successful charge
cycle is when the battery is charged to within 2.5% of the
full-charge float voltage. If a charge cycle is not successful
at EOC, the timer cycle resets and charging continues for
another full timer cycle.
When V
BAT
drops below 97.5% of the full-charge float
voltage, whether by battery loading or replacement of the
battery, the charger automatically reengages and starts
charging.
Preconditioning and Bad Battery Fault
A LT3652HV has a precondition mode, where charge cur
-
rent is limited to 15% of the programmed I
CHG(MAX)
, as
set by R
SENSE
. The precondition current corresponds to
15mV across R
SENSE
.
Precondition mode is engaged while the voltage on the
V
FB
pin is below the precondition threshold (2.3V, or
0.7 • V
BAT(FLT)
). Once the V
FB
voltage rises above the
precondition threshold, normal full-current charging can
commence. The LT3652HV incorporates 70mV of threshold
hysteresis to prevent mode glitching.
