lt3651-4.2 Linear Technology Corporation, lt3651-4.2 Datasheet - Page 15

• Manufacturer Part Number: lt3651-4.2
• Description: Monolithic 4a High Voltage Li-ion Battery Charger Features
• Manufacturer: Linear Technology Corporation

applicaTions inForMaTion
Status Pins
The LT3651 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 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 state following the table below. On
indicates the pin pulled low, and Off indicates pin high
impedance.
Table 1. Status Pins State Table
C/10 Termination
The LT3651 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 9mV across
R
the TIMER pin to ground.
When C/10 termination is used, a LT3651 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 LT3651 enters standby mode.
The CHRG status pin follows the charge 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.
SENSE
STATUS PINS STATE
CHRG
Off
Off
On
On
. This termination mode is engaged by shorting
BAT
drops below 97.5% of the full-charged float
FAULT
Off
On
Off
On
CHARGER STATUS
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
SENSE
.
There is no provision for bad battery detection if C/10
termination is used.
Timer Termination
The LT3651 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 end-of-cycle (t
based on C
so a typical 3 hour timer end-of-cycle would use 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 charge cycle until the charger
output current falls below the C/10 threshold. The charger
continues to “top off” the battery until timer end-of-cycle,
when the LT3651 terminates the charge cycle and enters
standby mode.
Termination at the end of the timer cycle only occurs if the
charge cycle was successful. A successful charge cycle
occurs when the battery is charged to within 2.5% of the
full-charge float voltage. If a charge cycle is not success-
ful at end-of-cycle, 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.
Precondition and Bad Battery Fault
A LT3651 charger has a precondition mode, in which
charge current is limited to 15% of the programmed I
as set by R
to 14mV across R
Precondition mode is engaged while the voltage on the BAT
pin is below the precondition threshold (V
C
TIMER
BAT
=
TIMER
SENSE
drops below 97.5% of the full-charge float
t
EOC
following the relation:
. The precondition current corresponds
3
(
SENSE
Hrs
TIMER
)
• .
.
0 68
) is connected from the TIMER
( )
µF
LT3651-4.2
BAT(PRE)
EOC
) occurs

). Once
365142f
MAX
,