Preliminary Datasheet

LP28056

LP28056 – 01 Ver. 1.1 Datasheet

FEB.-2012

www.lowpowersemi.com

Page 8 of 9

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 LP28056 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 LP28056. 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 consid-

erations are discussed further in the Applications Informa-

tion section.

Undervoltage Lockout (UVLO)

An internal undervoltage lockout circuit monitors the input

voltage and keeps the charger in shutdown mode until V

CC

rises above the undervoltage 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 V

CC

falls to within 30mV of the battery voltage. If the UVLO

comparator is tripped, the charger will not come out of

shutdown mode until V

voltage.

Manual Shutdown

At any point in the charge cycle, the LP28056 can be put

into shutdown mode by removing R

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 V

conditions. The STAT pin is in a high impedance state if

the LP28056 is in undervoltage lockout mode: either V

within 100mV of the BAT pin voltage or insufficient

voltage is applied to the V

Automatic Recharge

Once the charge cycle is terminated, the LP28056 continu-

ously monitors the voltage on the BAT pin using a com-

parator with a 2ms filter time (t

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 LP28056 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

LP28056 power dissipation is approximately:

Where PD is the total power dissipated within the IC,

calculated as:

efficiency at that particular load.

It is not necessary to perform worst-case power

dissipation scenarios because the LP28056 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 rotect the IC is:

Example: Consider the extreme case when an LP28056

is operating from a 6V supply providing 250mA to a 3V

Li-Ion battery, the switching regulator and the LDO are

off. The ambient temperature above which the LP28056

will begin to reduce the 250mA charge current is

double-sided 1 oz. copper board, the LP28056 has a

thermal resistance of approximately 43°C/W.)

T=

If there is more power dissipation due to the switching

regulator or the LDO, the thermal regulation will kick in

at a somewhat lower temperature than this. In the above

circumstances, the LP28056 can be used above 82.75°C,

but the charge current will be reduced from 250mA. The

approximate current at a given ambient temperature can

be calculated:

o

o

o

Note: 1V = 1J/C = 1W/A