February 2008
Rev 1
1/21
UM0497
User manual
USB Li-Ion battery charger evaluation board
Introduction
This document explains the functioning of the USB-based single cell Li-Ion battery charger
evaluation board which consists of a ST7260E2-based low-speed USB controller and a
battery charger based on the ST7LIT15BY0.
The evaluation board includes a power selector circuit to select the appropriate power
supply source and a step-up converter circuit based on the L6920 device to provide a fixed
output voltage to the USB controller. The power supply for the battery charger controller is
generated from the TL1431programmable voltage reference, keeping in mind the accuracy
requirement for charging. An additional current limiter is also included in series with a USB
power supply to show any incorrect behavior using a status LED.
A provision is provided on evaluation board such that any external low-speed USB controller
can control the operation of the charger, hence this system can be used with any low-speed
USB controller.
The charger used in the board utilizes a modified form of non-inverting buck-boost converter
to support the charging voltage requirement for single cell Li-Ion battery. This converter is
explained in more detail in AN2390.
This evaluation board represents a complete USB-based portable battery charging system
for a single cell Li-Ion battery, such as those used in MP3 players.
There are separate ICP connectors provided on the board to reprogram the USB controller
and charger controller.
