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LT3652

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NTC (Pin 8): Battery Temperature Monitor Pin. This pin is

the input to the NTC (Negative Temperature Coefﬁcient)

thermistor temperature monitoring circuit. This function is

enabled by connecting a 10kΩ, B = 3380 NTC thermistor

from the NTC pin to ground. The pin sources 50μA, and

monitors the voltage across the 10kΩ thermistor. When

the voltage on this pin is above 1.36 (T < 0°C) or below

0.29V (T > 40°C), charging is disabled and the CHRG and

FAULT pins are both pulled low. If internal timer termina-

tion is being used, the timer is paused, suspending the

charging cycle. Charging resumes when the voltage on NTC

returns to within the 0.29V to 1.36V active region. There

is approximately 5°C of temperature hysteresis associated

with each of the temperature thresholds. The temperature

monitoring function remains enabled while the thermistor

resistance to ground is less than 250k, so if this function

is not desired, leave the NTC pin unconnected.

BAT (Pin 9): Charger Output Monitor Pin. Connect a

10μF decoupling capacitance (CBAT) to ground. Depend-

ing on application requirements, larger value decoupling

capacitors may be required. The charge function operates

to achieve the programmed output battery ﬂoat voltage

(VBAT(FLT)) at this pin. This pin is also the reference for

the current sense voltage. Once a charge cycle is termi-

nated, the input bias current of the BAT pin is reduced to

< 0.1μA, to minimize battery discharge while the charger

remains connected.

SENSE (Pin 10): Charge Current Sense Pin. Connect the

inductor sense resistor (RSENSE) from the SENSE pin to the

BAT pin. The voltage across this resistor sets the average

charge current. The maximum charge current (ICHG(MAX))

corresponds to 100mV across the sense resistor. This

resistor can be set to program maximum charge cur-

rent as high as 2A. The sense resistor value follows the

relation:

RSENSE = 0.1/ICHG(MAX) (Ω)

Once a charge cycle is terminated, the input bias current of

the SENSE pin is reduced to < 0.1μA, to minimize battery

discharge while the charger remains connected.

BOOST (Pin 11): Bootstrapped Supply Rail for Switch

Drive. This pin facilitates saturation of the switch transistor.

Connect a 1μF or greater capacitor from the BOOST pin

to the SW pin. Operating range of this pin is 0V to 8.5V,

referenced to the SW pin. The voltage on the decoupling

capacitor is refreshed through a rectifying diode, with

the anode connected to either the battery output voltage

or an external source, and the cathode connected to the

BOOST pin.

SW (Pin 12): Switch Output Pin. This pin is the output

of the charger switch, and corresponds to the emitter of

the switch transistor. When enabled, the switch shorts

the SW pin to the VIN supply. The drive circuitry for this

switch is bootstrapped above the VIN supply using the

BOOST supply pin, allowing saturation of the switch for

maximum efﬁciency. The effective on-resistance of the

boosted switch is 0.175Ω.

SGND (Pin 13): Ground Reference and Backside Exposed

Lead Frame Thermal Connection. Solder the exposed lead

frame to the PCB ground plane.

PIN FUNCTIONS

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