lt3650-4.1 Linear Technology Corporation, lt3650-4.1 Datasheet - Page 10

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

LT3650-4.1/LT3650-4.2
OPERATION
The I
current sensed across the inductor current sense resistor,
allowing maximum charge current control by limiting the
effective voltage range of I
to 1V which, in turn, limits the current sense voltage to
100mV. This sets the maximum charge current, or the
current delivered while the charger is operating in con-
stant-current (CC) mode, which corresponds to 100mV
across R
also be manipulated through the RNG/SS pin (see the
RNG/SS: Dynamic Charge Current Adjust and RNG/SS:
Soft-Start sections).
If the voltage on the BAT pin is below V
engages precondition mode. During the precondition inter-
val, the charger continues to operate in constant-current
mode, but the maximum charge current is reduced to 15%
of the maximum programmed value as set by R
When the charger output voltage on the BAT pin approaches
the fl oat voltage (V
constant-voltage (CV) mode, and charge current is reduced
from the maximum value. As this occurs, the I
falls from the limit clamp and servos to lower voltages.
The IC monitors the I
detection of the C/10 charge current is achieved when
I
tion, this threshold is used to terminate the charge cycle.
Once the charge cycle is terminated, the CHRG status
pin becomes high impedance and the charger enters low
current standby mode.
The LT3650 contains an internal charge cycle timer that
terminates a successful charge cycle after a programmed
amount of time. This timer is typically programmed to
achieve end-of-cycle (EOC) in three hours, but can be
confi gured for any amount of time by setting an appropriate
10
TH
= 0.1V. If the charger is confi gured for C/10 termina-
TH
error voltage corresponds linearly to average
SENSE
. This maximum charge current level can
BAT(FLT)
TH
voltage as it is reduced, and
TH
), the charger transitions into
. A clamp limits this voltage
BAT(PRE)
, the LT3650
TH
SENSE
voltage
.
timing capacitor value (C
is used, the charge cycle does not terminate after C/10
is achieved. Because the CHRG status pin responds to
the C/10 current level, the IC will indicate a fully charged
battery status, but the charger will continue to source
low currents into the battery until the programmed EOC
time has elapsed, at which time the charge cycle will
terminate. At EOC, when the charging cycle terminates, if
the battery did not achieve at least 97.5% of the full fl oat
voltage, charging is deemed unsuccessful. The LT3650
will then re-initiate, and charging will continue for another
full timer cycle.
Use of the timer function also enables bad-battery detec-
tion. This fault condition is achieved if the battery does
not respond to preconditioning and the charger remains
in (or enters) precondition mode after one-eighth of the
programmed charge cycle time. A bad-battery fault halts
the charging cycle, the CHRG status pin goes high imped-
ance and the FAULT pin is pulled low.
When the LT3650 terminates a charging cycle, whether
through C/10 detection or by reaching timer EOC, the
average current mode analog loop remains active but
the internal fl oat voltage reference is reduced by 2.5%.
Because the voltage on a successfully charged battery
is at the full fl oat voltage, the voltage error amp detects
an overvoltage condition and rails low. When the voltage
error amp output drops below 0.3V, the IC enters standby
mode, where most of the internal circuitry is disabled, and
the V
on the BAT pin drops below the reduced fl oat reference
level, the output of the voltage error amp will climb, at
which point the IC comes out of standby mode and a new
charging cycle is initiated.
IN
bias current is reduced to 85μA. When the voltage
TIMER
). When timer termination
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