ACE4054

Fully integrated constant current/constant voltage

Li-ion battery charger

VER 1.4

12

Applications information

Stability Considerations

When a battery is connected to the output, the constant-voltage mode feedback is always stable.

However, in the case of absence of battery, an output capacitor is recommended to reduce ripple voltage.

In the case of high value capacitance or low ESR ceramic capacitors, a small value series resistor (~1

Ω)

is recommended. No series resistor is needed if tantalum capacitors are used.

In constant-current mode, the PROG pin is in the feedback loop, thus its impedance affects the stability.

The maximum allowed value of the program resistor is 20K, and additional capacitance reduces this value.

The pole frequency at the PROG pin needs to be kept above 100kHz to maintain device stability.

Therefore, the maximum resistance value can be calculated from the following equation, CPROG is the

capacitance loaded to the PROG pin.

Average rather than instantaneous charge current is more of a concern. A simple low pass filter can be

used on the PROG pin to measure the average battery current as shown in Figure 2. A 10K resistor has

been added between the PROG pin and the filter capacitor to ensure stability.

Figure 2. Isolating Capacitive Load PROG Pin and Filtering

Power Dissipation

The power dissipated in the IC causes the rise of die temperature. Most of the power dissipation is

caused by the internal power MOSFET, and can be calculated by the following equation:

Where PD is the power dissipated, VCC is the input supply voltage, VBAT is the battery voltage and

IBAT is the charge current. The approximate ambient temperature at which the thermal feedback begins

to protect the IC is:

Example: An ACE4054 operating from a 5V USB supply is programmed to supply 400mA full-scale

current to a discharged Li-Ion battery with a voltage of 3.75V. Assuming

ΘJA is 150℃ / W (see Board

Layout Considerations), the ambient temperature at which the ACE4054 will begin to reduce the charge

current is approximately:

– 3.75V) ∙ (400mA) ∙ 150℃ / W

∙ 150℃ / W = 120℃ - 75℃

ACE4054