ACE4054

Fully integrated constant current/constant voltage

Li-ion battery charger

VER 1.2

11

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:

The ACE4054 can be used above 45℃ ambient, but the charge current will be reduced from 400mA.

The approximate current at a given ambient temperature can be approximated by:

Using the previous example with an ambient temperature of 60℃, the charge current will be reduced to

approximately:

Moreover, when thermal feedback reduces the charge current, the voltage at the PROG pin is also

reduced proportionally as discussed in the operation section.

ACE4054