LT3650-8.2/LT3650-8.4
6
36508284fd
pin FuncTions
V
IN
(Pin 1): Charger Input Supply. V
IN
pin operating range
is 9V to 32V. V
IN
≥ 11.5V or (V
BOOST
– V
SW
) > 2V is re-
quired for start-up. I
VIN
= 85µA after charge termination.
CLP (Pin 2): System Current Limit Input. System current
levels can be monitored by connecting the input power
supply to the CLP pin and connecting a sense resistor
from the CLP pin to the V
IN
pin. Additional system load is
drawn from the V
IN
pin connection, and maximum system
load is achieved when V
CLP
– V
VIN
= 50mV. The LT3650
servos the maximum charge current required to maintain
programmed maximum system current. If this function is
not desired, connect the CLP pin to the V
IN
pin (see the
Applications Information section).
SHDN (Pin 3): Precision Threshold Shutdown Pin. The
enable threshold is 1.225V (rising), with 120mV of input
hysteresis. When in shutdown mode, all charging functions
are disabled. The precision threshold allows use of the
SHDN pin to incorporate UVLO functions. If the SHDN pin
is pulled below 0.4V, the IC enters a low current shutdown
mode where the V
IN
pin current is reduced to 15µA. Typi-
cal SHDN pin input bias current is 10nA. If the shutdown
function is not desired, connect the pin to the V
IN
pin.
CHRG (Pin 4): Open-Collector Charger Status Output;
typically pulled up through a resistor to a reference volt-
age. This status pin can be pulled up to voltages as high
as V
IN
when disabled, and can sink currents up to 10mA
when enabled. During a battery charging cycle, CHRG is
pulled low. When the charge cycle is terminated, the CHRG
pin becomes high impedance. If the internal timer is used
for termination, the pin stays low during the charging
cycle until the charge current drops below a C/10 rate, or
I
CHG(MAX)
/10. A temperature fault also causes this pin to
be pulled low (see the Applications Information section).
FAULT (Pin 5): Open-Collector Fault Status Output; typi-
cally pulled up through a resistor to a reference voltage.
This status pin can be pulled up to voltages as high as V
IN
when disabled, and can sink currents up to 10mA when
enabled. This pin indicates charge cycle fault conditions
during a battery charging cycle. A temperature fault causes
this pin to be pulled low. If the internal timer is used for
termination, a bad-battery
fault also causes this pin to
be
pulled low. If no fault conditions exist, the FAULT pin
remains high impedance (see the Applications Informa-
tion section).
TIMER (Pin 6): End-Of-Cycle Timer Programming Pin.
If a timer-based charge termination is desired, connect
a capacitor from this pin to ground. Full charge end-of-
cycle time (in hours) is programmed with this capacitor
following the equation:
t
EOC
= C
TIMER
• 4.4 • 10
6
A bad-battery fault is generated if the battery does not
reach the precondition threshold voltage within one-eighth
of t
EOC
, or:
t
PRE
= C
TIMER
• 5.5 • 10
5
A 0.68µF capacitor is typically used, which generates a
timer EOC at three hours, and a precondition limit time of
22.5 minutes. If a timer-based termination is not desired,
the timer function is disabled by connecting the TIMER
pin to ground. With the timer function disabled, charging
terminates when the charge current drops below a C/10
rate, or I
CHG(MAX)
/10.
RNG/SS (Pin 7): Charge Current Programming Pin. This
pin allows a dynamic adjustment of the maximum charge
current, and can be used to employ a soft-start function.
Maximum charge current is adjusted by setting the volt-
age on this pin
, such that the maximum desired voltage
across the
inductor current sense resistor (V
SENSE
– V
BAT
) is
0.1 • V
RNG/SS
, so the maximum charge current reduces to:
V
RNG/SS
• I
CHG(MAX)
This pin has an effective range from 0V to 1V. 50µA is
sourced from this pin, so the maximum charge current
can be programmed by connecting a resistor (R
RNG/SS
)
from RNG/SS to ground, such that the voltage dropped
across the resistor is equivalent to the desired program-
ming voltage, or:
V
RNG/SS
= 50µA • R
RNG/SS
Soft-start functionality can be implemented by connect-
ing a capacitor (C
RNG/SS
) from RNG/SS to ground, such
that the time required to charge the capacitor to 1V (full
