LTC4091 datasheet(7/26 Pages) LINER

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LTC4091

4091fa

For more information www.linear.com/LTC4091

PIN FUNCTIONS

SYNC (Pin 1): External Clock Synchronization Input. See

synchronizingsectioninApplicationsInformation.Ground

pin when not used.

VINGD (Pin 2): The VINGD pin is the open collector output

ofaninternalcomparator.VINGDremainshighimpedance

until sufficient voltage is present on VIN to enable the

switching regulator and RUN/SS is high.

RT(Pin3):OscillatorResistorInput.Connectingaresistor

to ground from this pin sets the switching frequency.

VC (Pin 4): High Voltage Buck Regulator Control Pin. The

voltage on this pin controls the peak switch current in the

high voltage regulator. Tie an RC network from this pin

to ground to compensate the control loop.

NTC (Pin 5): Input to the NTC Thermistor Monitoring

Circuits. The NTC pin connects to a negative temperature

coefficient thermistor which is typically co-packaged with

the battery pack to determine if the battery is too hot or too

cold to charge. If the battery temperature is out of range,

charging is paused until the battery temperature re-enters

the valid range. A low drift bias resistor is required from

VNTC to NTC and a thermistor is required from NTC to

ground. If the NTC function is not desired, the NTC pin

should be grounded.

VNTC (Pin 6): Output Bias Voltage for NTC. A resistor

from this pin to the NTC pin will bias the NTC thermistor.

HVPR (Pin 7): Open-Drain High Voltage Present Output

(Active Low). A low on this pin indicates that the high volt-

age regulator has sufficient voltage to charge the battery.

CHRG(Pin8):Open-DrainChargeStatusOutput.Whenthe

battery is being charged, the CHRG pin is pulled low by an

internal N-channel MOSFET. When the timer runs out or

the charge current drops below 10% of the programmed

charge current or the input supply is removed, the CHRG

pin is forced to a high impedance state.

PROG (Pin 9): Charge Current Program Pin. Connecting a

resistorfromPROGtogroundprogramsthechargecurrent:

ICHG(A)=

52,500V

RPROG

GATE (Pin 10): External Ideal Diode Gate Connection. This

pin controls the gate of an optional external P-channel

MOSFET transistor used to supplement the internal ideal

diode. The source of the P-channel MOSFET should be

connected to OUT and the drain should be connected to

BAT. When not in use, this pin should be left floating. It

is important to maintain high impedance on this pin and

minimize all leakage paths.

BAT (Pins 11, 12): Single-Cell Li-Ion Battery. This pin is

used as an output when charging the battery and as an

input when supplying power to OUT. When the OUT pin

potential drops below the BAT pin potential, an ideal diode

function connects BAT to OUT and prevents OUT from

droppingmorethan100mVbelowBAT.Aprecisioninternal

resistor divider sets the final charge voltage on this pin.

OUT (Pin 13): Voltage Output. This pin is used to provide

controlled power to a load from either the primary input

(VIN) or the battery (BAT). OUT should be bypassed with

at least 68µF to GND.

V4P1 (Pin 14): 4.1V Charge Voltage Select Pin. Leave this

pin disconnected to select a 4.2V charge voltage. Connect

this pin to the BAT pin to select a 4.1V charge voltage.

Care should be taken to avoid leakage on the V4P1 pin if

it is left open.

GND (Pin 15): Ground Pin.

NC (Pin 16): No Connect. Nothing is connected to this pin.

TIMER (Pin 17): Timer Capacitor. Placing a capacitor,

CTIMER, to GND sets the timer period. The timer period is:

tTIMER(hours)=CTIMER (F)•RPROG (Ω)•300

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