LP4055-03

Apr.-2017

www.lowpowersemi.com

Page 6 of 8

Preliminary Datasheet

LP4055

Stability Considerations

The constant-voltage mode feedback loop is stable without an

output capacitor provided a battery is connected to the

charger output. With no battery present, an output capacitor is

recommended to reduce ripple voltage. When using high

value, low ESR ceramic capacitors, it is recommended to add

a 1Ω resistor in series with the capacitor. No series resistor is

needed if tantalum capacitors are used.

Manual Shutdown

At any point in the charge cycle, the LP4055 can be put into

drain current to less than 1µA and the supply current to less

than 1µA. A new charge cycle can be initiated by

reconnecting the program resistor. The CHRG pin is in a

high impedance state if the LP4055 is in undervoltage lockout

insufficient voltage is applied to the VCC pin.

Automatic Recharge

Once the charge cycle is terminated, the LP4055 continuously

monitors the voltage on the BAT pin using a comparator with

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.

CHRG output enters a strong pull-down state during recharge

cycles.

Under voltage Lockout (UVLO)

An internal under voltage lockout circuit monitors the input

rises above the under voltage lockout threshold .The UVLO

circuit has a built-in hysteresis of 500mV. Furthermore, to

protect against reverse current in the power MOSFET, the

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

is tripped, the charger will not come out of shutdown mode

Power Dissipation（SOT23-5）

The conditions that cause the LP4055 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:

Where PD is the power dissipated, VCC 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:

VCC Bypass Capacitor

Many types of capacitors can be used for input bypassing;

however, caution must be exercised when using multilayer

ceramic capacitors. Because of the self-resonant and high Q

characteristics of some types of ceramic capacitors, high

voltage transients can be generated under some start-up

conditions, such as connecting the charger input to a live

power source .Adding a 1.5Ω resistor in series with an X5R

ceramic capacitor will minimize start-up voltage transients.

Layout Considerations

For the main current paths as indicated in bold lines, keep

their traces short and wide.

Put the input and output capacitor as close as possible to the

device pins (VCC, BAT and GND).

Connect all analog grounds to a command node and then

connect the command node to the power ground behind the

output capacitors.