ACE4054

Fully integrated constant current/constant voltage

Li-ion battery charger

VER 1.4

13

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.

It is important to remember that ACE4054 applications do not need to be designed for worst-case

thermal conditions sine the IC will automatically reduce power dissipation when the junction temperature

reached approximately 120℃.

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. Feedthrough 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 ACE4054 operating from a 5V wall adapter is programmed to supply 600mA full-scale

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

charge current at an ambient temperature of 25℃ is:

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