Standalone Linear Li-ion Battery Charger with Thermal Regulation

2007-7-3

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FSP4054

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 FSP4054 applications do not

need to be designed for worst-case thermal conditions since the IC will automatically reduce power dissipation when

the junction temperature reaches approximately 120°C.

Increasing Thermal Regulation Current

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

This has the effect of increasing the current delivered to the battery during thermal regulation. One method is by

dissipating some of the power through an external component, such as a resistor or diode.

Example: An FSP4054 operating from a 5V wall adapter is programmed to supply 800mA full-scale current to a

ambient temperature of 25°C 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

Figure 3: A circuit to maximize thermal mode charge current

regulated charge current to be:

While this application delivers more energy to the battery and reduces charge time in thermal mode, it may actually

lengthen charge time in voltage mode if VCC becomes low enough to put the FSP4054 into dropout. Figure 4 shows

Remember to choose a resistor with adequate power handling capability.