lt3650-4.1 Linear Technology Corporation, lt3650-4.1 Datasheet - Page 6

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

PIN FUNCTIONS
LT3650-4.1/LT3650-4.2
V
4.75V to 32V. V
for start-up. I
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
drawn from the V
load is achieved when V
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
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
cal SHDN pin input bias current is 10nA. If the shutdown
function is not desired, connect the pin to the V
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
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
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
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
6
CHG(MAX)
IN
(Pin 1): Charger Input Supply. V
IN
when disabled, and can sink currents up to 10mA
/10. A temperature fault also causes this pin to be
VIN
IN
≥ 7.5V or (V
IN
= 85μA after charge termination.
IN
pin connection, and maximum system
pin current is reduced to 15μA. Typi-
CLP
IN
pin. Additional system load is
BOOST
– V
VIN
IN
– V
= 50mV. The LT3650
pin operating range is
SW
) > 2V is required
IN
pin (see the
IN
pin.
IN
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:
A bad-battery fault is generated if the battery does not
reach the precondition threshold voltage within one-eighth
of t
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
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
0.1 • V
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
from RNG/SS to ground, such that the voltage dropped
across the resistor is equivalent to the desired program-
ming voltage, or:
Soft-start functionality can be implemented by con-
necting a capacitor (C
such that the time required to charge the capacitor to 1V
t
t
V
V
EOC
EOC
PRE
RNG/SS
RNG/SS
RNG/SS
, or:
= C
= C
CHG(MAX)
TIMER
TIMER
• I
= 50μA • R
, so the maximum charge current reduces to:
CHG(MAX)
• 4.4 • 10
• 5.5 • 10
/10.
RNG/SS
RNG/SS
6
5
) from RNG/SS to ground,
SENSE
– V
RNG/SS
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BAT
) is
)