LT3651-8.2_15 Datasheet, PDF (8/24 Pages) Linear Technology – Monolithic 4A High Voltage 2-Cell Li-Ion Battery Charger

LT3651-8.2/LT3651-8.4
PIN FUNCTIONS
and can sink currents up to 10mA when enabled. CHRG
is pulled low during a battery charging cycle. 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 approximately 10%
of the maximum charge current. A temperature fault also
causes this pin to be pulled low.
SHDN (Pin 27): Shutdown Pin. This pin can be used for
precision UVLO functions. When this pin rises above the
1.20V threshold, the part is enabled. The pin has 95mV of
voltage hysteresis. When in shutdown mode, all charging
functions are disabled. When 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 17µA. Typical SHDN pin
input bias current is 10nA. Connect the pin to V_IN if the
shutdown function is not desired.
I_LIM (Pin 28): Input Current Limit Programming. This pin
allows for setting and dynamic adjustment of the system
input current limit, and can be used to employ a soft-start
function. The voltage on this pin sets the maximum input
current by setting the maximum voltage across the input
current sense resistor, placed between CLP and CLN.
The effective range on the pin is 0V to 1V. 50µA is sourced
from this pin usually to a resistor (R_ILIM) to ground. V_IILIM
represents approximately 11 times the maximum voltage
across the input current sense resistor. If no R_ILIM is used
the part will default to maximum input current.
Soft-start functionality for input current can be imple-
mented with a capacitor (C_ILIM) from I_LIM to ground. The
soft-start capacitor and the programming resistor can be
implemented in parallel.
CLP/CLN (Pin 29/Pin 30): System Current Limit Positive
and Negative Input. System current levels are monitored
by connecting a sense resistor from the input power sup-
ply to the CLP pin, connecting a sense resistor from the
CLP pin to the CLN pin and then connecting CLN to V_IN.
The system load is then delivered from the CLN pin. The
LT3651-8.2/LT3651-8.4 servo the maximum charge cur-
rent required to maintain programmed maximum system
current. The system current limit is set as a function of
the voltage on the I_LIM pin and the input current sense
resistor. This function is disabled by shorting CLP, CLN
and V_IN together.
V_IN (Pins 32, 33, 34): Charger Input Supply. These pins
provide power for the LT3651-8.2/LT3651-8.4. Charge
current for the battery flows into these pins. I_VIN is less
than 100µA after charge termination. Connect the pins
together.
RNG/SS (Pin 35): Charge Current Range and Soft-Start
Pin. This pin allows for setting and dynamic adjustment
of the maximum charge current, and can be used to em-
ploy a soft-start function. The voltage on this pin sets the
maximum charge current by setting the maximum voltage
across the charge current sense resistor, R_SENSE , placed
between SENSE and BAT.
The effective range on the pin is 0V to 1V. 50µA is sourced
from this pin usually to a resistor (R_RNG/SS) to ground.
V_RNG/SS represents approximately 10 times the maximum
voltage across the charge current sense resistor. If no R_RNG/
SS ^{is used the part will default to maximum charge current.}
Soft-start functionality for charge current can be imple-
mented by connecting a capacitor (C_RNG/SS) from RNG/SS
to ground. The soft-start capacitor and the programming
resistor can be implemented in parallel. The RNG/SS pin
is pulled low during fault conditions, allowing graceful
recovery from faults if C_RNG/SS is used.
RT (Pin 36): Switcher Oscillator Timer Set Pin. A resis-
tor from this pin to ground sets the switcher oscillator
frequency. Typically this is 54.9k for f_OSC = 1MHz.
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