BC3770 Datasheet, PDF (15/45 Pages) Freescale Semiconductor, Inc – 2.0 A Switch-Mode Charger

5.3.5.3 Fast-charge Mode (Constant-current Mode)
The Fast-charge mode is entered in t_PRECHG when the battery voltage exceeds the V_{VSYS_MIN} threshold of a typical 3.6 V. During this
mode, the battery is charged with a programmable fast-charge current. The fast-charge current is programmable from 100 mA to 2000 mA
with a 500 mA default. Fast-charge current is always limited by the input current limit setting. As soon as the battery voltage reaches the
V_{VSYS_MIN} threshold, VSYS tracks the battery voltage through the Q4. This is called 'tracking mode”. In tracking mode, power dissipation
is minimized by RDSON_Q4 x IFAST_CHG. However, if the VSYS voltage drops during the fast-charge mode, the charge current is
automatically reduce to keep the dropout voltage, to ensure proper operation of charging circuitry. During this fast-charge mode, the safety
timer called fast charge timer, t_{FAST_TMR}, counts. If the battery voltage does not reach the V_{BAT_REG} threshold before the timer expires,
charging is suspended and a fault signal is asserted via the INTB pin. This timer is programmable and is disabled by default. This timer
is automatically disabled when the input current limit is set to 100 mA.
5.3.5.4 Full-charge Mode (Constant-Voltage Mode)
As soon as the BATREG voltage reaches the V_{BAT_REG} threshold, the fast-charge current is reduced to a programmable top-off current.
The V_{BAT_REG} regulation threshold is programmable from 4.1 V to 4.475 V in 25 mV steps.
5.3.5.5 Top-off Mode (Constant-voltage Mode)
If the charge current down to a pre-programmed top-off current threshold is sensed over t_ITOPOFF, the safety timer called top-off timer,
t_{TOPOFF_TMR}, 45-minute by default, automatically counts. The top-off interrupt event is reported to the processor via the INTB. As soon
as the processor reads the interrupt registers, the processor is able to turn off the charger by either CHGENB = H, CHGEN = 0, or wait
until the timer expires in AUTOSTOP=1. The top-off current is programmable from 100 mA to 650 mA in 50 mA steps. 100 mA is the
default.
5.3.5.6 Done Mode (Constant-voltage Mode)
After the top-off timer expires, the charger is Off automatically in AUTOSTOP=1. However, the charger stays at CV (Constant-voltage
mode) in AUTOSTOP=0 even though the top-off timer expires. The interrupt signal of Done is reported to the processors via the INTB pin,
regardless of the AUTOSTOP status.
5.3.6 Boost (OTG) Mode
Similar to Charge mode operation, in OTG mode enabled by I²C control bit, ENBOOST = 1, the device provides a regulated output voltage
to VBUS from the battery. In Boost mode, the device first converts the battery voltage to a target voltage at PMID, then bypasses it to the
VBUS pin with load current up to 900 mA to support USB OTG devices. In order to have a final regulated output at VBUS, the minimum
input at BATREG should be at least or above 3.0 V. To activate Boost mode, all of the following conditions should be met in advance.
1. Either the CHGEN bit resets to “0” or CHGENB = HIGH (meaning for “charger disabled”)
2. The VBUS voltage must be less than the UVLO falling threshold
3. No Fault Conditions
4. SUSPEN bit reset to “0”
Then set the ENBOOST bit to “1”. In this Boost mode, the following functions are consequently disabled.
• AICL
• Charging
5.3.6.1 Soft-start in BOOST Mode
When Boost mode is enabled, the PMID is regulated to a pre-programmed voltage. After PMID reaches a preset target regulation voltage,
the FET between PMID and VBUS turns On slowly to minimize the inrush current. The output current limit is ramped up to the boost output
current limit. This soft-start counter is not initialized when one of next conditions occur.
1. Die temperature exceeds T_SD
2. No battery detection (NOBAT = H) on NOBAT
3. Voltage on VBUS rises over V_{BUS_OVP}
4. Voltage on the BATREG pin rises over V_{BAT_MAX_BO}
5. Voltage on the BATREG pin falls below V_{STOP_BO}
BC3770
Analog Integrated Circuit Device Data
15
Freescale Semiconductor