lt3650-4.1 Linear Technology Corporation, lt3650-4.1 Datasheet - Page 15

• Manufacturer Part Number: lt3650-4.1
• Description: High Voltage 2 Amp Monolithic Li-ion Battery Charger
• Manufacturer: Linear Technology Corporation

Status Pins
The LT3650 reports charger status through two open-col-
lector outputs, the CHRG and FAULT pins. These pins can
accept voltages as high as V
when enabled.
The CHRG pin indicates that the charger is delivering
current at greater than a C/10 rate, or one-tenth of the
programmed 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 the pin pulled low, and Off indicates pin high
impedance:
Table 1. Status Pins State Table
If the battery is removed from an LT3650 charger that is
confi gured 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 LT3650 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 the maximum current, as programmed with R
The C/10 threshold current corresponds to 10mV across
R
the TIMER pin to ground.
When C/10 termination is used, an LT3650 charger sources
battery charge current as long as the average current level
remains above the C/10 threshold. As the full-charge fl oat
APPLICATIONS INFORMATION
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)
IN
, and can sink up to 10mA
CHARGER STATUS
SENSE
.
voltage is achieved, the charge current falls until the C/10
threshold is reached, at which time the charger terminates
and the LT3650 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 LT3650 supports a timer-based termination scheme, in
which a battery charge cycle is terminated after a specifi c
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 three hours, which requires
a 0.68μF capacitor.
The CHRG status pin continues to signal charging at a
C/10 rate, regardless of which 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
LT3650 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 occurs when the battery is charged to within 2.5%
of the full-charge fl oat voltage. If a charge cycle is not
successful at EOC, the timer cycle resets and charging
continues for another full timer cycle.
When V
voltage, whether by battery loading or replacement of
the battery, the charger automatically re-engages and
starts charging.
C
TIMER
TIMER
BAT
BAT
= t
following the relation:
drops below 97.5% of the full-charged fl oat
LT3650-4.1/LT3650-4.2
drops below 97.5% of the full-charge fl oat
EOC
• 2.27 • 10
TIMER
) is connected from the TIMER
–7
(Hours)
EOC
) occurs based
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