L6924D datasheet(11/38 Pages) STMICROELECTRONICS

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L6924D

Operation description

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Operation description

The L6924D is a fully integrated battery charger that allows a very compact battery

management system for space limited applications. It integrates in a small package, all the

power elements: power MOSFET, reverse blocking diode and the sense resistor.

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 2.5V) the L6924D can also

work as a Quasi-Pulse charger when powered from a current limited adapter. To work in this

condition, is enough to set the device’s charging current higher than the adapter one

(Chapter 7.4 on page 19). The advantage of the linear charging approach is that the device has

a direct control of the charging current and so the designer needn’t to rely on the upstream

adapter. However, the advantage of the Quasi-Pulse approach is that the power dissipated

inside the portable equipment is dramatically reduced.

Regards the charging approach, the L6924D charges the battery in three phases:

●

Pre-Charge constant current: in this phase (active when the battery is deeply

discharged) the battery is charged with a low current.

●

Fast-Charge constant current: in this phase the device charges the battery with the

maximum current.

●

Constant Voltage: when the battery voltage is closed to the selected output voltage, the

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

The full flexibility is provided by:

●

Programmable pre-charging current and voltage thresholds (IPRETH and VPRETH)

(Chapter 7.2 on page 18, Chapter 7.3 on page 19).

●

Programmable fast-charging current (ICHG) (Chapter 7.4 on page 19).

●

Programmable end of charge current threshold (IENDTH) (Chapter 7.5 on page 20).

●

Programmable end of charge timer (TMAXCH) (Chapter 7.8 on page 22).

If the full flexibility is not required and a smaller number of external components is preferred,

default values of IPRETH and VPRETH are available leaving the respective pins floating.

●

If a PTC or NTC resistor is used, the device can monitor the battery temperature in order

to protect the battery from operating in unsafe thermal conditions.

●

Beside the good thermal behavior guaranteed by low thermal resistance of the package,

additional safety is provided by the built-in temperature control loop. The IC monitors

continuously its junction temperature. When the temperature reaches approximately

120°C, the thermal control loop starts working, and reduces the charging current, in order

to keep the IC junction temperature at 120°C.

●

Two open collector outputs are available for diagnostic purpose (status pins ST1 and ST2).

They can be also used to drive external LEDs or to interface with a microcontroller.

●

The voltage across the resistor connected between IEND and GND gives information about

the actual charging current (working as a Gas Gauge), and it can be easily fed into a µC

ADC.

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