L6924D operation description

AN4050

6/19

DocID022816 Rev 2

2

L6924D operation description

The L6924D is a fully monolithic battery charger dedicated to single-cell Li-Ion/polymer

battery packs. It is designed with BCD6 technology and integrates all of the power elements

(the Power MOSFET, reverse blocking diode and the sense resistor) in a small VFQFPN16

3 mm x 3 mm package.

It normally works as a linear charger when powered from an external voltage regulated

adapter. However, thanks to its very low minimum input voltage (down to 2.5 V) the L6924D

can also work as a quasi-pulse charger when powered from a current limited adapter,

dramatically reducing the power dissipation.

The L6924D charges the battery in three phases:

•

Pre-charge constant current: a deeply discharged battery is charged with a low current.

•

Fast-charge constant current: the device charges the battery with the maximum

current.

•

Constant voltage: when the battery voltage is close to the selected output voltage, the

device starts to reduce the current, until the charge termination is completed.

Regardless of the charging approach, a closed loop thermal control avoids device

overheating. The L6924D allows the user to program many parameters, such as pre-charge

current, fast-charge current, pre-charge voltage threshold, end-of-charge current threshold,

and charge timer. The L6924D offers two open collector outputs for diagnostic purposes,

which can be used to either drive two external LEDs or communicate with a host

microcontroller. Finally, the L6924D also provides other battery related functions, such as

checking for battery presence, monitoring, and protection from unsafe thermal conditions.

Figure 6. Basic application schematic