USB-Powered Li+ Charger

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7

Charging from AC Adapters

The MAX1811 also operates from sources other than

USB ports. The full charging input voltage range is

4.35V to 6.5V. When charging in the 500mA mode with

an AC adapter, rely on the thermal loop to limit the

power dissipation by limiting the charge current at

higher input voltages if limited PC board area is avail-

able to dissipate heat.

Capacitor Selection

Use a minimum of 2.2µF placed close to BATT for prop-

er stability. Bypass IN to GND with a 4.7µF capacitor.

Use a larger input bypass capacitor for high input volt-

ages or high charging current to reduce supply noise.

Chip Information

TRANSISTOR COUNT: 1907

PROCESS: BiCMOS

4.375V

4.735V

0.015V

4.640V

0.110V

4.625V

0.125V

4.500V

*4.400V

0.000V

4.397V

0.003V

4.378V

0.002V

4.350V

0.025V

4.750V

0.000V

LOW-POWER

FUNCTION

BUS-POWERED

HUB

HOST OR

POWERED HUB

REFERENCED

TO HUB

REFERENCED

TO SOURCE

*UNDER TRANSIENT CONDITIONS, SUPPLY AT HUB CAN DROP FROM 4.00V TO 4.070V.

Figure 3. USB Voltage Specification

MAX1811

SELI

EN

SELV

IN

4.35V TO 6.5V

4.2V

4.1V

ON

OFF

100mA

500mA

BATT

GND

GND

CHG

TO IN

TO LOAD

SINGLE

Li+

CELL

CHG

LOGIC OUT

LED

10k

Ω

Figure 4. Charging from a USB Port