Analog Integrated Circuit Device Data

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19

Freescale Semiconductor

BC3770

5.3.9

Safety Timer

There are three safety timers on the device: a pre-charge timer, a fast charge timer, and a top-off timer. The pre-charge is fixed at 45

following.

1. Pre-charge timer is reset in one or more of the following ways:

• BATREG crosses over the VSYS minimum threshold of 3.6 V

• Falling VBUS UVLO detected

• CHGENB = HIGH

2. Fast-charge timer is reset in one or more of the following ways:

• Falling VBUS UVLO detected

• CHGENB=HIGH or CHGEN reset to “0” before expiration

3. Top-off timer is reset in one or more of the following ways:

AUTOSTOP = 1

• Falling VBUS UVLO detected

• CHGENB = HIGH or CHGEN reset to “0” before expiration

However, all safety timers are reset commonly in the following fault conditions:

• BAT OVP detected

• VBUS OVP detected

• Thermal shutdown

If all fault conditions are released, the timer resumes to start.

5.3.10 VSYS

maximum input limit programmed value.

The device regulates the system supply voltage, VSYS (3.6 V), in Trickle and Pre-charge mode, which allow the application system to be

booted up even in dead or deeply discharged battery. The device has the system output, VSYS, priority over charge current, which gives

the required load for the system while reducing the charge current, if the input current is limited. System path also allows accurate charge

cycle since it allows the system to know precisely when the charging current has hit the current termination threshold vs. implementations,

where the battery and the system are connected to the same node. When the battery voltage crosses the minimum system voltage

insures the minimum power dissipation on the device comes true. When the battery charging is completed, the system node, VSYS, is

to the battery voltage.

Figure 7. VSYS Tracking BATTEG

BATREG and VSYS

3.6V