ACE4054C

500mA/1.5A Standalone Linear Li-Ion Battery Charge

VER 1.2

12

Thermal Considerations

Due to its compact size, it is of great importance to use a good thermal PC board. Good thermal

conduction increases maximum allowed charge current value.

The thermal path for the heat generated by the IC is from the die to the copper lead frame, through the

package leads, (especially the ground lead) to the PC board copper. The PC board copper is the heat

sink. The footprint copper pads should be as wide as possible and expand out to larger copper areas to

spread and dissipate the heat to the surrounding ambient. Feed through vias to inner or backside copper

layers are also useful in improving the overall thermal performance of the charger. Other heat sources on

the board, not related to the charger, must also be considered when designing a PC board layout

because they will affect overall temperature rise and the maximum charge current.

Increasing Thermal Regulation Current

Reducing the voltage drop across the internal MOSFET can significantly decrease the power dissipation

in the IC. Minimized power dissipation results in reduced die temperature rise and hence equivalent

increased charge current in thermal regulation. One way is to bypass some of the current through an

external component, such as a resistor or diode.

Example: An ACE4054C operating from a 5V wall adapter is programmed to supply 600mA full-scale

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

Assuming

Θ

By dropping voltage across a resistor in series with a 5V wall adapter (shown in Figure 3), the on-chip

power dissipation can be decreased, thus increasing the thermally regulated charge current

ACE4054C

Figure 3. A Circuit to Maximize Thermal Mode Charge Current

VCC Bypass Capacitor

Due to their self-resonant and high Q characteristics, some types of ceramic capacitors can cause high

voltage transients under some start-up conditions (i.e connecting the charger input to a live power source).

Adding a small value resistor in series with the ceramic capacitor can minimize start-up voltage transients