AAT3670 データシートの表示（PDF） - Advanced Analogic Technologies

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AAT3670

1.6A Dynamic Battery Charger and Power Manager

Advanced Analogic Technologies 

BatteryManagerTM

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AAT3670

1.6A Dynamic Battery Charger and Power Manager

default USBH value and USBL is subsequently set for

100mA. In the USBL fast charge mode, the constant

charging current is set to 20 percent of the programmed

USBH. More simply put, the USBL low fast charge level

= USBH divided by five. The USBH or USBL modes may

be externally selected by USB select pin (USBSEL).

In the USBH mode, the battery cell preconditioning or

trickle charge current is fixed at 10 percent of the pro-

grammed fast charge constant current. In the USBL mode,

the trickle charge current is only reduced to 50 percent of

the programmed fast charge constant current level.

When the USBSEL pin is connected to a logic high level,

the USBH level will be active. Conversely, when USBSEL

is pulled to a logic low level (ground) the USBL level will

be used for fast charging. Refer to Table 2 for the recom-

mended RUSBSET value to program the desired USB input

constant current charge levels.

USB Charge Reduction

In many instances, product system designers have an

issue of not knowing the real properties of a potential

USB port to be used to supply power to the battery char-

ger. Typical powered USB ports commonly found on

desktop and notebook PCs should supply up to 500mA.

In the event a USB port being used to supply the charger

is unable to provide the programmed fast charge cur-

rent, or if the system under charge must also share sup-

ply current with other functions causing an overload to

the USB port, the AAT3670 will automatically reduce

USB fast charge current to maintain port integrity and

protect the host system.

The USB charge reduction system becomes active when

the voltage on the USB input falls below the USB charge

reduction threshold (VCHRUSB), which is typically 4.5V.

Regardless of which USB charge function is selected

(USBH or USBL), the charge reduction system will

reduce the fast charge current level in a linear fashion

until the voltage sensed on the USB input recovers

above the charge reduction threshold voltage. The USB

charge reduction threshold (VCHRUSB) may be externally

set to a value lower than 4.5V by placing a resistor

divider network between VUSB and ground with the cen-

ter connected to the CHRUSB pin. The USB charge

reduction feature may be disabled by shorting the

CHRUSB pin directly to the USB input pin.

The following equation may be used to approximate a

USB charge reduction threshold below 4.5V:

Eq.

2:

VUSBCHR

=

2.0V

(R2/[R2 +

R1])

where R1 and R2 < 1MΩ

VUSB

USB

R1

CHRUSB

R2

1.0M

VCHR = 2.0V

800k

Figure 4: Internal Equivalent Circuit for the

CHRUSB Pin.

USB Input Charge Inhibit and Resume

The AAT3670 under-voltage lockout (UVLO) and power-

on reset feature will function when the USB input pin

voltage level drops below the UVLO threshold. At this

point the charger will suspend charging. When power is

re-applied to the USB pin or the UVLO condition recovers,

the system charge control will assess the state of charge

on the battery cell and will automatically resume charging

in the appropriate mode for the condition of the battery.

End of Charge Termination

The AAT3670 provides a user-programmable charge ter-

mination current at the end of the charge cycles. When

the battery cell voltage as sensed by the BATS pin reach-

es 4.2V, the charge control will transition from constant

current fast charge mode to constant voltage mode. In

constant voltage mode, the battery cell voltage will be

regulated at 4.2V. The charge current will drop as the

battery reaches its full charge capacity. When the charge

current drops to the programmed end of charge (EOC)

current, the charge cycle is complete and the charge

controller terminates the charging process.

3670.2008.04.1.5

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