ACE4054

Fully integrated constant current/constant voltage

Li-ion battery charger

VER 1.2

9

Charge Termination

The ACE4054 keeps monitoring the PROG pin during the charging process. It terminates the charge

cycle when the charge current falls to 1/10th the programmed value after the final float voltage is reached.

When the PROG pin voltage falls below 100mV for longer than tTERM (typically 1ms), charging is

terminated. The charge current is latched off and the ACE4054 enters standby mode, where the input

supply current drops to 200μA. (Note: C/10 termination is disabled in trickle charging and thermal limiting

modes).

During charging, the transient response of the circuit can cause the PROG pin to fall below 100mV

temporarily before the battery is fully charged, thus can cause a premature termination of the charge

cycle. A 1ms filter time (tTERM) on the termination comparator can prevent this from happening. Once the

average charge current drops below 1/10th the programmed value, the ACE4054 terminates the charge

cycle and ceases to provide any current through the BAT pin. In this state, all loads on the BAT pin must

be supplied by the battery.

The ACE4054 constantly monitors the BAT pin voltage in standby mode and resume another charge

cycle if this voltage drops below the recharge threshold (VRECHRG). User can also manually restart a

charge cycle in standby mode either by removing and then reapplied the input voltage or restart the

charger using the PROG pin. A diagram of typical charge cycle is shown in figure 1.

Charge Status Indicator (CHRG)

There are three different states of the charge status output, namely strong pull-down (~10mA), weak

pull-down (~20μA) and high impedance. The strong pull-down state indicates that the ACE4054 is in a

charge cycle. When the charge cycle has terminated, the pin state is then determined by undervoltage

lockout conditions. If VCC meets the UVLO conditions, device is in weak pull-down statues and is ready

to charge. If the difference between Vcc and BAT pin voltage is less than 100mV or insufficient voltage is

applied to the VCC pin, High impedance appears on the charge statues pin.

Thermal Limiting

Build-in feedback circuitry mechanism can reduce the value of the programmed charge current once the

die temperature tends to rise above 120℃, hence prevents the temperature from further increase and

ensure device safe operation.

Undervoltage Lockout (UVLO)

Build-in undervoltage lockout circuit monitors the input voltage and keeps the charger in shutdown mode

until VCC rises above the 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

Floating the PROG pin by removing the resistor from PROG pin to ground can put the device in

shutdown mode. The battery drain current is thus reduced to less than 5μA and the supply current to less

than 50μA. Reconnecting the resistor back will restart a new charge cycle.

Once manually shutdown, the CHRG pin is in a weak pull-down state if VCC is above UVLO voltage.

The CHRG pin is in a high impedance state if the ACE4054 is in undervoltage lockout mode.