6

FN6541.1

April 3, 2008

Block Diagram

USB Charge Current

When the EN pin is pulled low and a valid USB voltage is

present at the USB pin, the IC will charge the battery at a

rate dependent on the IUSB setting. The charge current

maybe reduced by the USB source if it is set to a value

higher than the current limit of the USB source.

Equation 1 for setting the IUSB current is as follows:

The current set by the IUSB pin for charging the battery is in

addition to current drawn by the load on the USB_BYP. The

system designer should consider the maximum expected

USB_BYP load current when selecting the USB charging

current so as not to exceed the current limits set by the USB

standards.

path, VUSB to BAT is 600m

Ω. If the entire USB current limit

of 465mA is being supplied to the battery, the drop across

the charging FET could be more than 300mV. Thus, the

voltage at the USB pin needs to be maintained above ~4.5V.

Otherwise, the period to charge the battery may be

prolonged.

Adapter Charge Current

When the EN pin is pulled low and a valid adapter voltage is

present at the VDC pin, the IC will charge the battery at a

rate dependent on the IVDC setting; the charge on the

battery and the source connected to the VDC pin. An

example of this is while the IVDC is set for 1000mA, the

adapter supply may only provide 800mA and the battery is

limited to the 800mA.

600m

Ω. At a 1.0A charging rate, 600mV is dropped across

the charge path. Thus, the voltage at the VDC pin needs to

be maintained above ~4.80V. Otherwise the period to charge

the battery may be prolonged.

It is recommended that the maximum charging current be

programmed to between 100mA and 1200mA.

5.4VOVP

VOLTAGE/CURRENT CONTROLLER

THERM

USB_BYP

IMIN

IUSB

IDC

VUSB

VDC

LDO

BAT

EN

PPR

CHG

GND

I/O CNTL

4.35V TO 6.5V

4.35V TO 5.25V

6.8VOVP

+

-

+

-

+

-

1.22V

+

-

+

-

+

VDC

VUSB

150/80mV

VOS

VOS

+

-

+

-

2.6V

3.9V

VMIN

VRCH

+

-

4.2V

CC/CV

LDO

BYPASS

FIGURE 1. SIMPLIFIED BLOCK DIAGRAM

IUSB

6820

R

IUSB

------------------ mA

()

=

(EQ. 1)

IVDC

6820

R

IVDC

------------------ mA

()

=

(EQ. 2)

ISL9221