Preliminary Datasheet

LP78092

LP78092 – 00 Version 1.0 Feb.-2014

www.lowpowersemi.com

Page 9 of 10

The LP78092 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 SET pin. Figure 2 shows the state diagram

of a typical charge cycle.

Charge Status Indicator (STAT)

The charge status output has two different states: strong

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

state indicates that the LP78092 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 LP78092 is in under voltage lockout mode: either V

than 100mV above the BAT pin voltage or insufficient voltage is

applied to the V

A microprocessor can be used to distinguish between these two

states—this method is discussed in the Applications Information

section.

Function

CHRG(pin15)

STDBY(pin14)

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

LP78092 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 LP78092. 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.

TQFN-16 power considerations are discussed further in the

Applications Information section.

Automatic Recharge

Once the charge cycle is terminated, the LP78092 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.

Start-up Function

The LP78092 features an LDO regulator enable/disable

function. To assure the LDO regulator will switch on, the EN

turn on control level must be greater than 1.4 volts but not

above Vin+0.3V. The LDO regulator will go into the shutdown

mode when the voltage on the EN pin falls below 0.4 volts. For

protecting the system, the LP78092 have a quick-discharge

function. If the enable function is not needed in a specific

application, it may be tied to VIN to keep the LDO regulator in a

continuously on state.

Feedback Capacitor and Voltage

For adjustable version, connecting a 22pF between output pin

and FB pin significantly reduces output voltage ripple, it is

critical that the capacitor connection should be direct and PCB

traces should be as short as possible.

The output voltage of dual LDO could be set by the formula

below:

Considering the practical application, we may add a small

capacitor with R1 in parallel which could be 33pF or 47pF.