LP3947 datasheet(11/14 Pages) NSC

11 / 14 page

Application Notes (Continued)

MODE PIN

The mode pin toggles the LP3947 between the AC adaptor

mode and the USB mode. When CHG-IN is connected to a

USB port, this pin must be set low. When CHG-IN is con-

nected to an AC adaptor, this pin must be tied high to either

the BATT pin or to the wall adaptor input. Caution: MODE pin

should never be tied to CHG-IN pin directly, as it will turn on

an internal diode.

5.6 HR SAFETY TIMER IN CHARGER MODE

The LP3947 has a built-in 5.6 hr back up safety timer to

prevent over-charging a Li Ion battery. The 5.6 hr timer starts

counting when the charger enters the constant current

mode. It will turn the charger off when the 5.6 hr timer is up

while the charger is still in constant current mode. In this

case, both LEDs will turn on, indicating a fault condition.

When the battery temperature is outside the specified tem-

perature range, the 5.6 hr safety timer will reset upon recov-

ery of the battery temperature.

2C INTERFACE

2C interface is used in the LP3947 to program various

parameters as shown in Table 3. The LP3947 operates on

default settings following power up. Once programmed, the

LP3947 retains the register data as long as the battery

voltage is above 2.85V.

20111010

FIGURE 5. Power Up Timing Diagram in Charger Mode (1.39V < Ts < 2.427V)

20111011

FIGURE 6. Power Up Timing Diagram in LDO Mode (Ts

≥ 2.7V)

LP3947 bảng dữ liệu(PDF) 11 Page - National Semiconductor (TI)