AN2370 Datasheet, PDF (1/14 Pages) STMicroelectronics – 800 mA standalone linear Li-Ion

AN2370
Application note
800 mA standalone linear Li-Ion
battery charger with thermal regulation
Introduction
One way to minimize the size and complexity of a battery charger is to use a linear-type
charger. The linear charger drops the AC adapter voltage down to the battery voltage. The
number of external components is low: linear chargers require input and output bypass
capacitors, and sometimes need an external pass transistor, and resistors for setting voltage
and current limits.
The main pitfall of a linear charger is power dissipation. The charger simply drops the AC
adapter voltage down to the battery voltage.
In the case of a 0.8 A charger, a 5 V±10% regulated AC adapter voltage, and battery voltage
that varies between 4.2 V and 2.5 V, the power dissipation can range from 0.64 W to 2.0 W.
This type of charger is simpler than the switch-mode type, mainly because the passive LC
filter is not required. It dissipates the most power when the battery voltage is at its minimum,
since the difference between the fixed input voltage and the battery voltage is greatest
during this condition.
Figure 1. STC4054 battery charge board
October 2007
Rev 4
1/14
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