Preliminary Datasheet

LP78090

LP78090 – 00

Version 1.0

Feb.-2014

www.lowpowersemi.com

Page 9 of 10

The LP78090 constantly monitors the BAT pin voltage in

standby mode. If this voltage drops below the 4.05V recharge

threshold (V

once again supplied to the battery. To manually restart a charge

cycle when in standby mode, the input voltage must be

removed and reapplied, or the charger must be shut down and

restarted using the ISET pin. Figure 2 shows the state diagram

of a typical charge cycle.

Charge Status Indicator

The charge status output has two different states: strong

pull-down (~10mA) and high impedance. The strong pull-down

state indicates that the LP78090 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 LP78090 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—this method is discussed in the Applications Information

section.

Function

CHRG(pin8)

STDBY(pin7)

Charging

Low

High

charge completed

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

LP78090 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 LP78090. 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.

Automatic Recharge

Once the charge cycle is terminated, the LP78090 continuously

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

2ms filter time (t

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.