9

than 2

µA 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

conditions. The CHRG pin is in a high impedance state if

is within 100mV of the BAT pin voltage or insufficient voltage

Automatic Recharge

Once the charge cycle is terminated, the KB4540 continu-

ously monitors the voltage on the BAT pin using a com-

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.

meets the UVLO conditions and the KB4540 is ready to

charge. High impedance indicates that the KB4540 is in

above the BAT pin voltage or insufficient voltage is applied

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

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

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

comparator is tripped, the charger will not come out of

voltage.

Manual Shutdown

At any point in the charge cycle, the KB4540 can be put

PROG pin. This reduces the battery drain current to less

TRICKLE CHARGE

MODE

1/10TH FULL CURRENT

BAT > 2.9V

BAT < 2.9V

BAT > 2.9V

CHRG: STRONG

PULL-DOWN

CHARGE MODE

FULL CURRENT

CHRG: STRONG

PULL-DOWN

SHUTDOWN MODE

CHRG: Hi-Z IN UVLO

WEAK PULL-DOWN

OTHERWISE

PROG

RECONNECTED

OR

UVLO CONDITION

STOPS

PROG FLOATED

OR

UVLO CONDITION

POWER ON

PROG < 100mV

STANDBY MODE

NO CHARGE CURRENT

CHRG: WEAK

PULL-DOWN

2.9V < BAT < 4.05V

Figure 1. State Diagram of a Typical Charge Cycle

KB4540

Kingbor Technology Co.,Ltd

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OPERATION