LP4054

Aug.-2017

Email: marketing@lowpowersemi.com

www.lowpowersemi.com

Page 6 of 7

Preliminary Datasheet

LP4054

Thermal Limit

An internal thermal feedback loop reduces the programmed

charge current if the die temperature attempts to rise above a

preset value of approximately 125℃. This feature protects the

LP4054 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 LP4054. 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 150mV of the battery voltage. If the UVLO

comparator is tripped, the charger will not come out of

shutdown mode until VIN raises 150mV above the battery

voltage.

Automatic Recharge

Once the charge cycle is terminated, the LP4054 continuously

monitors the voltage on the BAT pin using a comparator with

a 2ms filter time (TRECHARGE). A charge cycle 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.

CHRG output enters a strong pull-down state during recharge

cycles.

Power Dissipation

The conditions that cause the LP4054 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=125℃-PDθJA

TA=125℃-(VIN-VBAT)×IBAT×θJA

Example: An LP4054 operating from a 5V USB supply is

programmed to supply 300mA full-scale current to a

discharged Li-Ion battery with a voltage of 3.75V. Assuming

θJA is 250 ℃/W (see Board Layout Considerations), the

ambient temperature at which the LP4054 will begin to reduce

the charge current is approximately:

TA=125℃-(5V-3.75V)×(300mA)×250℃/W

TA=125℃-0.375W×250℃/W=31.25℃

Moreover, when thermal feedback reduces the charge current,

the voltage at the ISET pin is also reduced proportionally as

discussed in the Operation section. It is important to

remember that LP4054 applications do not need to be

designed for worst-case thermal conditions since the IC will

automatically reduce power dissipation when the junction

temperature reaches approximately 125℃.

VIN 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 capacitor as close as possible to the device

pins (VIN and GND).



Connect all analog grounds to a command node and

then connect the command node to the power ground

behind the output capacitors.