Simplify Battery Charging from the USB – Design Note 320
John Shannon
Introduction
The USB is fast becoming the most popular way to attach peripherals to personal computers. An important
feature of the USB standard is that it allows for power
transmission over the USB cable, making it possible for
a PDA or other handheld device to charge its battery
while it is connected to a host PC. The charger is based on the LTC4053—a standalone
timer-terminated constant current/constant voltage
linear charger. The LTC4053 features a thermal loop
which maximizes the charging rate under all conditions by regulating the maximum die temperature. Less
sophisticated linear chargers must run lower charging
rates or risk overheating, thus increasing charge times. The USB specification defines load current limits that
USB peripherals can draw from the USB. Three operating modes are allowed: Operation of the LTC4053 is simple. The charge current
is set by a resistor on the PROG pin, the termination
timer period is set by a capacitor on the timer pin and
float voltage is preset at 4.2V. Suspend mode, where the USB peripheral draws
less than 500ОјA from the USB cable L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their
respective owners. Low power mode, where the current consumption
can be up to 100mA LTC4053
1
USB …