Kingbor Technology Co.,Ltd
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KB4540
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 V
CC
is high enough to exceed the UVLO
conditions. The CHRG pin is in a high impedance state if
the KB4540 is in undervoltage lockout mode: either V
CC
is within 100mV of the BAT pin voltage or insufficient voltage
is applied to the V
CC
pin.
Automatic Recharge
Once the charge cycle is terminated, the KB4540 continu-
ously monitors the voltage on the BAT pin using a com-
parator with a 2ms filter time (t
RECHARGE
). A charge cycle
restarts when the battery voltage falls below 4.05V (which
corresponds to approximately 80% to 90% battery capac-
ity). 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 ON
BAT < 2.9V
TRICKLE CHARGE
MODE
1/10TH FULL CURRENT
CHRG: STRONG
PULL-DOWN
BAT > 2.9V
SHUTDOWN MODE
I
CC
DROPS TO <25µA
CHRG: Hi-Z IN UVLO
WEAK PULL-DOWN
OTHERWISE
CHARGE MODE
FULL CURRENT
CHRG: STRONG
PULL-DOWN
PROG < 100mV
STANDBY MODE
NO CHARGE CURRENT
PROG FLOATED
OR
UVLO CONDITION
CHRG: WEAK
PULL-DOWN
2.9V < BAT < 4.05V
BAT > 2.9V
OPERATION
lockout conditions. A weak pull-down indicates that V
CC
meets the UVLO conditions and the KB4540 is ready to
charge. High impedance indicates that the KB4540 is in
undervoltage lockout mode: either V
CC
is less than 100mV
above the BAT pin voltage or insufficient voltage is applied
to the V
CC
pin. A microprocessor can be used to distin-
guish between these three states—this method is dis-
cussed in the Applications Information section.
Thermal Limiting
An internal thermal feedback loop reduces the programmed
charge current if the die temperature attempts to rise
above a preset value of approximately 120°C. This feature
protects the KB4540 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 KB4540. 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 consid-
erations are discussed further in the Applications Informa-
tion section.
Undervoltage Lockout (UVLO)
An internal undervoltage lockout circuit monitors the input
voltage and keeps the charger in shutdown mode until V
CC
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 V
CC
falls to within 30mV of the battery voltage. If the UVLO
comparator is tripped, the charger will not come out of
shutdown mode until V
CC
rises 100mV above the battery
voltage.
Manual Shutdown
At any point in the charge cycle, the KB4540 can be put
into shutdown mode by removing R
PROG
thus floating the
PROG pin. This reduces the battery drain current to less
PROG
RECONNECTED
OR
UVLO CONDITION
STOPS
Figure 1. State Diagram of a Typical Charge Cycle
9
KINGBOR [ KINGBOR TECHNOLOGY CO ]
