LTC4120 datasheet(7/24 Pages) AD

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LTC4126-ADJ

Rev. 0

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BAT Quiescent Current

(DC/DC Off) vs Temperature

DC/DC Output Transient Response

to Load Step

VCC = 0V

VBAT = 3.1V

VBAT = 3.8V

TEMPERATURE (°C)

–20

–5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

4126-ADJ G19

COUT = 2.2µF

TIME (800µs/DIV)

–80

–60

–40

–20

–10

4126-ADJ G20

VOUT

LOAD CURRENT

TYPICAL PERFORMANCE CHARACTERISTICS T

A = 25°C, unless otherwise noted.

PIN FUNCTIONS

NTC (Pin 1): Thermistor Input. Connect a thermistor from

NTC to GND, and a bias resistor from VCC to NTC. The volt-

age level on this pin determines if the battery temperature

is safe for charging. The charge current and charge timer

are suspended if the thermistor indicates a temperature

that is unsafe for charging. Once the temperature returns

to the safe region, charging resumes. Ground the NTC pin

if temperature qualified charging is not needed.

EN (Pin 2): Digital Logic Input Pin to Enable the DC/DC

Converter.Aminimumvoltageof1.1Venablestheregulator

providedthattheLTC4126-ADJisnotinbatterydisconnect

mode(seeBatteryDisconnect/ShipMode underOperation

section). A low voltage (0.4V max) disables the regulator

and allows the pushbutton to control it. If only pushbutton

control is desired, tie this pin to GND. Tie this pin to BAT

if the DC/DC needs to remain enabled all the time. Do not

leave this pin unconnected.

PBEN (Pin 3): Pushbutton Toggle Input Pin to enable/

disable the DC/DC converter. Enabling of the regulator can

only occur if the LTC4126-ADJ is not in battery disconnect

mode(seeBatteryDisconnect/ShipMode underOperation

section). A weak internal pull-up forces PBEN high when

not driven. A normally open pushbutton is connected

from PBEN to GND to force a low state on this pin when

the button is pushed. However, the pushbutton is ignored

if the EN input is high. If the pushbutton function is not

needed, leave this pin unconnected.

PROG (Pin 4): Charge Current Program Pin. A 1% resis-

tor, RPROG, connected from PROG to GND programs the

charge current as such:

RPROG =

100•1.1V

ICHG

– 2.2kΩ

with ICHG being the desired battery charge current. The

minimum and maximum resistances allowed for RPROG

are 0Ω and 107kΩ, respectively. Do not leave this pin

unconnected.

ACPR (Pin 5): Digital CMOS Logic Output Pin to indicate

if there is enough input power available to charge the bat-

tery. This pin goes high when the VCC-to-BAT differential

voltage rises above 80mV (typical) and goes low when the

differential voltage drops below 27mV (typical). The low

level of this pin is referenced to GND and the high level

is referenced to the OUT pin voltage. Consequently, this

indicator is not available if the DC/DC is disabled.

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