LT3652 LINER [Linear Technology], LT3652 Datasheet - Page 19

• Manufacturer Part Number: LT3652
• Description: Power Tracking 2A Battery Charger for Solar Power
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
Status Pins
The LT3652 reports charger status through two open
collector outputs, the CHRG and FAULT pins. These pins
can accept voltages as high as V
10mA when enabled.
The CHRG pin indicates that the charger is delivering
current at greater that a C/10 rate, or 1/10th of the pro-
grammed maximum charge current. The FAULT pin signals
bad battery and NTC faults. These pins are binary coded,
and signal following the table below, where ON indicates
pin pulled low, and OFF indicates pin high-impedance:
If the battery is removed from an LT3652 charger that is
configured for C/10 termination, a sawtooth waveform
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 LT3652 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
The C/10 threshold current corresponds to 10mV across
R
the TIMER pin to ground.
SENSE
STATUS PINS STATE
CHRG
OFF
OFF
ON
ON
. This termination mode is engaged by shorting
FAULT
OFF
OFF
ON
ON
Not Charging — Standby or Shutdown Mode
Bad Battery Fault (Precondition Timeout / EOC
Failure)
Normal Charging at C/10 or Greater
NTC Fault (Pause)
CHARGER STATUS
IN
, and can sink up to
SENSE
.
When C/10 termination is used, a LT3652 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 LT3652 enters standby mode.
The CHRG status pin follows the charger cycle, and is high
impedance when the charger is not actively charging.
When V
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 LT3652 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
pin to ground. The timer cycle EOC (T
on C
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 cur-
rent falls below the C/10 threshold. The charger continues
to top-off the battery until timer EOC, when the LT3652
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
C
TIMER
TIMER
BAT
= T
following the relation:
drops below 97.5% of the full-charged float
EOC
• 2.27 x 10
TIMER
) is connected from the TIMER
–7
EOC
(Hours)
) occurs based
LT3652
19
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