LP28012 datasheet(7/10 Pages) POWER

7 / 10 page

Preliminary Datasheet

LP28012

LP28012 – 00

Feb.-2014

Email: marketing@lowpowersemi.com

www.lowpowersemi.com

Page 7 of 10

states—this method is discussed in the Applications Information

section.

Function

STAT1(pin2)

STAT2(pin3)

Charging

Low

High

Charge END

High

Low

Thermal Limiting

An internal thermal feedback loop reduces the ISET rammed

charge current if the die temperature attempts to rise above a

preset value of approximately 120°C. This feature protects the

LP28012 from excessive temperature and allows the user to

push the limits of the power handling capability of a given circuit

board without risk of damaging the LP28012. The charge

current can be set according to typical (not worst-case) ambient

temperature with the assurance that the charger will

automatically reduce the current in worst-case conditions.

TDFN power considerations are discussed further in the

Applications Information section.

Under voltage Lockout (UVLO)

An internal under voltage lockout circuit monitors the input

voltage and keeps the charger in shutdown mode until VCCrises

above the under voltage lockout threshold. The UVLO circuit

has a built-in hysteresis of 200mV. Furthermore, to protect

against reverse current in the power MOSFET, the UVLO circuit

keeps the charger in shutdown mode if VCC falls to within 30mV

of the battery voltage. If the UVLO comparator is tripped, the

charger will not come out of shutdown mode until VCC rises

100mV above the battery voltage.

Manual Shutdown

At any point in the charge cycle, the LP28012 can be put into

shutdown mode by removing RISET thus floating the ISET pin.

This reduces the battery drain current to less than 2µA and the

supply current to less than 50µA. A new charge cycle can be

initiated by reconnecting the ISETram resistor.

In manual shutdown, the STAT pin is in a weak pull-down state

as long as VCC is high enough to exceed the UVLO conditions.

The STAT pin is in a high impedance state if the LP28012 is in

under voltage lockout mode: either VCC is within 100mV of the

BAT pin voltage or insufficient voltage is applied to the VCC pin.

Automatic Recharge

Once the charge cycle is terminated, the LP28012 continuously

monitors the voltage on the BAT pin using a comparator with a

2ms filter time (tRECHARGE). A charge cycle restarts when the

battery voltage falls below 4.05V (which corresponds to

approximately 80% to 90% battery capacity). This ensures that

the battery is kept at or near a fully charged condition and

eliminates the need for periodic charge cycle initiations. STAT

output enters a strong pull-down state during recharge cycles.

Power Dissipation

The conditions that cause the LP28012 battery charger to

reduce charge current through thermal feedback can be

approximated by considering the total power dissipated in

the IC. For high charge currents, the LP28012 power

dissipation is approximately:

Where PD is the total power dissipated within the IC, ADP is

the input supply voltage, VBAT is the battery voltage, IBAT is

the charge current and PD_BUCK is the power dissipation due

to the regulator. PD_BUCK can be calculated as:

Where VOUTB is the regulated output of the switching

regulator, IOUTB is the regulator load and is the regulator

efficiency at that particular load.

It is not necessary to perform worst-case power dissipation

scenarios because the LP28012 will automatically reduce

the charge current to maintain the die temperature at

approximately 125°C. However, the approximate ambient

temperature at which the thermal feedback begins to protect

the IC is:

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