芯美 子
Thermal Limiting
AAP2154
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 AAP2154 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 AAP2154. 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.
Figure 7. State Diagram of a Typical Charge Cycle
Manual Shutdown
At any point in the charge cycle, the AAP2154 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 AAP2154 is in undervoltage
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 AAP2154
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.
DS2154 Ver1.0 Aug. 2007
12
系 ：15999644579 83151715
EUTECH [ EUTECH MICROELECTRONICS INC ]
