BIPB PIN

BIPB pin is used to select between charger mode and LDO

mode. It is pulled HIGH internally to the CHG-IN pin, which is

the LDO mode. To select charger mode, this pin must be

connected to ground directly or pulled to ground via the

battery pack ID resistor. In the latter case, BIPB pin pulled

LOW confirms battery connection. Alternatively, this pin can

be pulled to LOW by the system micro-controller for added

flexibility.

LDO MODE

The charger is in the LDO mode when the BIPB pin is left

open or HIGH. This mode of operation is used primarily

during system level testing of the handset to eliminate the

need for battery insertion. CAUTION: battery may be dam-

aged if device is operating in LDO mode with battery con-

nected.

The internal power FET provides up to 1.2 amp of current at

BATT pin in this mode. The LDO output is set to 4.1V. When

operating at higher output currents, care must be taken not

to exceed the package power dissipation rating. See “Ther-

mal Performance of LLP Package” section for more detail.

EN PIN

The Enable pin is used to enable/disable the charger, in both

charger mode and LDO mode, see Figure 5 and Figure 6.

The Enable pin is internally pulled HIGH to the CHG-IN pin.

When the charger is disabled, it draws less than 4 µA of

current.

5.6 HR SAFETY TIMER IN CHARGER MODE

Both LP3945 and LP3946 have 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 constant cur-

rent 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.

In order for the 5.6 hr safety timer to function in the LP3945,

pin 13 should be left floating. CAUTION: disabling the back

up safety timer could create unsafe charging conditions. If

disabled, user must provide external protection to prevent

overcharging the battery.

StopModeEN PIN

To provide the flexibility of using an external back up timer,

StopModeEN allows “bypassing” of the 5.6 hr safety timer. It

is achieved by pulling pin 13 on the LP3945 to LOW. As

indicated in the LP3945 Flow Chart, this feature works only

in constant current mode with a Li Ion battery. Therefore, if a

Li Ion battery is in constant current mode and the 5.6 hr timer

times out, instead of the charger being turned off, it proceeds

to maintenance mode.

This is not a recommended mode of operation. Disabling the

5.6 hr timer can potentially expose the battery to prolong

charge cycle and damage the battery. If StopModeEn feature

is used, user must protect the battery from exposure to

prolong charge cycle. For normal operation, pin 13 should be

left floating.

20066515

FIGURE 5. Power Up Timing Diagram in Charger Mode (BIPB = LOW)

20066516

FIGURE 6. Power Up Timing Diagram in LDO Mode (BIPB = HIGH)

www.national.com

12