BC3770 Datasheet, PDF (14/45 Pages) Freescale Semiconductor, Inc – 2.0 A Switch-Mode Charger

5.3 Operational Modes
5.3.1 Undervoltage Lockout (UVLO)
The BC3770 has a typical undervoltage lockout threshold of 3.8 V, with a 200 mV hysteresis, rising on VBUS. VSYS also has a falling
2.5 V typical with 200 mV hysteresis. When the input supply voltage is below the 3.6 V typical UVLO falling level, the PWM buck converter
turns off.
5.3.2 Registers Reset
All programmable registers in the device are reset to the default values when the following condition is met.
• Reset Condition: VSYS V_{SYS_UVLO}
5.3.3 Q4 FET On in NO VALID VBUS
If the battery is connected with the voltage above a typical of 2.4 V and no any valid input power source is attached, the Q4 FET between
VSYS and CHGOUT turns On and connects the Battery to the system, regardless of status of SHDNB. The VL regulator stays off.
5.3.4 Charge Mode
The BC3770 performs the following pre-qualification process before initiating the Charging mode:
1. Input Voltage: Detect the validation of VBUS power source, charger enable threshold, and Adaptive-Input Current Limit (AICL)
threshold. If the falling VBUS hits the AICL threshold, the charging current is reduced to limit the amount of drop on VBUS power
source. In addition, the device senses the input voltage is at least above BATREG + 150 mV.
2. Battery Presence Detection: Detect the status of battery presence through the NOBAT pin. If the voltage on the NOBAT pin is
above the logic high threshold, the charging is suspended (Internal Q4 FET is open). However, VSYS is regulated at VVSYS_MAX
as long as a valid input source is attached.
3. Battery Voltage: Sense the battery voltage if it is less than the BAT OVP threshold.
4. Die Temperature: If the die temperature is above 130 °C or less than 150 °C, charging is suspended.
5. Overvoltage Detection (OVP): Sense if the VBUS is less than the OVP threshold. If the OVP condition is detected, the PWM
converter is immediately shut off.
6. Validation of Software and Hardware Enable signals: Detect the status of software enable bit, CHGEN=1, SUSPEN=0, and
hardware pin of CHGENB=LOW.
This pre-qualification process is continuously monitored and charging is suspended until all conditions are met.
5.3.5 CHARGING PROFILE
5.3.5.1 Trickle-charge Mode
Trickle-charge mode is automatically enabled in 27 ms after the VSYS start-up time expires. The battery is charged with a fixed 90 mA
charge current until the battery voltage reaches the threshold, 2.5 V typical in rising. This threshold is not programmable over I²C. As soon
as the battery voltage crosses over the threshold, a pre-charge mode is activated automatically after the fixed deglitch time. This allows
the protection circuit in the battery pack to be reset with no damage, and brings the battery voltage to a higher level.
5.3.5.2 Pre-charge Mode
The Pre-charge mode is enabled in t_TRICKLE when the battery voltage crosses over a typical 2.5 V. The safety timer called pre-charge
timer, t_{PRECHG_TMR}, 45-minute counts at the same time as well. This timer is reset as soon as the Fast-charge mode is initiated. This
allows a deeply discharged battery to charge safely. The pre-charge current is programmable from 150 mA to 450 mA in 100 mA steps
over I²C. If the battery voltage does not exceed the V_{VSYS_MIN} threshold before the timer expires, charging is suspended and a fault signal
is asserted via the INTB pin. If the VSYS voltage drops due to the limited input power source during the mode, the charge current is
automatically reduce to maintain the VSYS as low as at 3.4 V. If the load is still overloaded, even in no charge current and limited input
current, the VSYS can't help the collapse.
Analog Integrated Circuit Device Data
Freescale Semiconductor
BC3770
14