Figure 3a : Primary Side of Battery Charger

Figure 3a and 3b show the primary and the secondary sides of the battery charger (SMPS type, primary

and secondary sides) where the VIPER20, the ST62T25C and TSM102A are combined to ensure safe

charging of two Li-Ion battery cells in parallel (main and spare batteries).

The Viper20 ensures with a very low component count the energy transfer from the off-line primary side

to the secondary side thanks to its PWM ability ( with externally adjustable frequency of operation) and

integrated high voltage avalanche-rugged vertical MOSFET.

The ST62T25C

µController is used to :

• recognize the Li-Ion battery type (4.1V or 4.2V and capacity)

• manage the charging of the two different cells in parallel thanks to the proper command of two power

switches

• prevent the battery charging in case of overtemperature or undertemperature

• drive adequate LEDs for convenient visual information

The TSM102A can ensure all analog interfacing between the batteries and the

µP by

• controlling current and voltage with adequate feedback via the optocoupler to the primary side

• offering highly precise voltage reference for all measurements

• amplifying the current signal through the sense resistor to be monitored by the µController

• providing a low cost solution for 5V power supply of the MCU

AN1051 - APPLICATION NOTE

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