LP4054 datasheet(10/14 Pages) ETC

10 / 14 page

Preliminary

LP4054

LP4054-datasheet V1.0

Sep.-2006

10-10

these three states –this method is discussed in the

Applications Information section.

Charge Termination

An internal thermal feedback loop reduces the

programmed charge current if the die temperature

attempts to rise above a preset value of approximately

120℃. 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. ThinSOT power considerations

are discussed further in the Applications Information

section.

Undervoltage Lockout (UVLO)

An internal undervoltage lockout circuit monitors the

input voltage and keeps the charger in shutdown mode

until VCC 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 VCC falls to within 30mV of

the battery voltage. If the UVLO comparator is tripped,

the charger will not come out of shutdown mode until

VCC rises 100mV above the battery voltage.

Manual Shutdown

At any point in the charge cycle, the LP4054 can

be put into shutdown mode by removing RPROG

thus floating the PROG 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

program resistor. In manual shutdown, the

CHRG pin is in a weak

pull-down state as long as VCC is high enough to

exceed the UVLO conditions. The CHRG pin is in a high

impedance state if the LP4054 is in under voltage

lockout mode: either VCC is within 100mV of the BAT

pin voltage or insufficient voltage is applied to the VCC

pin.

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.

Application Information

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. In constant-current mode,

the PROG pin is in the feedback loop, not the battery.

The constant-current mode stability is affected by the

impedance at the PROG pin. With no additional

capacitance on the PROG pin, the charger is stable with

program resistor values as high as 20k. However,

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