LP28056S datasheet(7/8 Pages) POWER

7 / 8 page

LP28056S-02

May.-2013

Email: marketing@lowpowersemi.com

www.lowpowersemi.com

Page 7 of 8

Preliminary Datasheet

LP28056S

Charge Status Indicator (STAT)

The charge status output has two different states:

strong pull-down (~5mA) and high impedance. The

strong pull-down state indicates that the LP28056S is

in a charge cycle. Once the charge cycle has

terminated, the pin state is determined by under

voltage lockout conditions. High impedance indicates

that the LP28056S is in under voltage lockout mode:

either VIN is less than 100mV above the BAT pin

voltage or insufficient voltage is applied to the VIN

pin. A microprocessor can be used to distinguish

between these two states.

Charge Stage

STAT1 Status

STAT2 Status

Charging

Low

High

Charge Complete

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 150°C. This feature protects the

LP28056S 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 LP28056S. 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.

Under voltage Lockout (UVLO)

An internal under voltage lockout circuit monitors the

input voltage and keeps the charger in shutdown

mode until VIN rises 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 VIN falls to

within 30mV of the battery voltage. If the UVLO

comparator is tripped, the charger will not come out

of shutdown mode until VIN rises to 100mV above the

battery voltage.

Power Dissipation

The conditions that cause the LP28056S to reduce

charge current through thermal feedback can be

approximated by considering the power dissipated in

the IC. Nearly all of this power dissipation is

generated by the internal MOSFET. This is

calculated to be approximately:

PD=(VIN-VBAT)×IBAT

Where PD is the power dissipated, VIN is the input

supply voltage, VBAT is the battery voltage and IBAT is

the charge current. The approximate ambient

temperature at which the thermal feedback begins to

protect the IC is:

TA=150℃-PD×θJA

TA=150℃-(VIN-VBAT)×IBAT×θJA

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