BQ24273 Datasheet, PDF (14/27 Pages) Texas Instruments – 2.5A, Single Input, Single Cell Switchmode Li-Ion Battery Charger with Integrated Current Sense

bq24273
SLUSB08 – JUNE 2012
www.ti.com
Input Voltage Protection in Charge Mode
Sleep Mode
The bq24273 enters the low-power sleep mode if the voltage on V_SUPPLY falls below sleep-mode entry threshold,
V_BAT+V_SLP, and V_VBUS is higher than the undervoltage lockout threshold, V_UVLO. This feature prevents draining
the battery during the absence of V_SUPPLY. When V_SUPPLY < V_BAT+ V_SLP, the bq24273 turns off the PWM
converter and sends a single 128μs pulse on the STAT and INT outputs and updates the STATx and FAULT_x
bits in the status registers. Once V_SUPPLY > V_BAT+ V_SLP, the STATx and FAULT_x bits are cleared and the device
initiates a new charge cycle.
Input Voltage Based DPM
During normal charging process, if the input power source is not able to support the programmed or default
charging current, the supply voltage will decease. Once the supply drops to V_{IN_DPM} (default 4.76V), the input
current limit is reduced down to prevent further supply droop. When the IC enters this mode, the charge current
is lower than the set value and the DPM_STATUS bit is set (Bit 5 in Register 05H). This feature ensures IC
compatibility with adapters with different current capabilities without a hardware change.
Bad Source Detection
When a source is connected to IN, the bq24273 runs a Bad Source Detection procedure to determine if the
source is strong enough to provide some current to charge the battery. A current sink is turned on (75mA) for
32ms. If the source is valid after the 32ms (V_BADSOURCE < V_SUPPLY < V_OVP), the buck converter starts up and
normal operation continues. If the supply voltage falls below V_{BAD_SOURCE} during the detection, the current sink
shuts off for 2s and then retries, a single 128μs pulse is sent on the STAT and INT outputs and the STATx and
FAULT_x bits of the status registers and the battery/supply status registers are updated in the I²C. The detection
circuits retries continuously until a valid source is detected after the detection time. If during normal operation the
source falls to V_{BAD_SOURCE}, the bq24273 turns off the PWM converter and sends a single 128μs pulse is sent on
the STAT and INT outputs and the STATx and FAULT_x bits of the status registers and the battery/supply status
registers are updated in the I2C. Once a good source is detected, the STATx and FAULT_x bits are cleared and
the device returns to normal operation.
Input Over-Voltage Protection
The bq24273 provides over-voltage protection on the input that protects downstream circuitry. The built-in input
over-voltage protection to protect the device and other components against damage from overvoltage on the
input supply (Voltage from V_IN to PGND). During normal operation, if V_SUPPLY > V_OVP, the bq24273 turns off the
PWM converter and sends a single 128μs pulse is sent on the STAT and INT outputs and the STATx and
FAULT_x bits of the status registers and the battery/supply status registers are updated in the I2C. Once the
OVP fault is removed, the STATx and FAULT_x bits are cleared and the device returns to normal operation.
To allow operation with some unregulated adapters, the OVP circuit is not active during Bad Source Detection.
This provides some time for the current sink to pull the unregulated adapter down into an acceptable range. If the
adapter voltage is high at the end of the detection, the startup of the PWM converter does not occur. The OVP
circuit is active during normal operation, so if the system standby current plus the charge current is not enough to
pull down the source, operation is suspended.
Charge Status Outputs (STAT, INT)
The STAT output is used to indicate operation conditions for bq24273. STAT is pulled low during charging when
EN_STAT bit in the control register (0x02h) is set to “1”. When charge is complete or disabled, STAT is high
impedance. When a fault occurs, a 128-µs pulse (interrupt) is sent out to notify the host. The status of STAT
during different operation conditions is summarized in Table 1. STAT drives an LED for visual indication or can
be connected to the logic rail for host communication. The EN_STAT bit in the control register (00H) is used to
enable/disable the charge status for STAT. The interrupt pulses are unaffected by EN_STAT and will always be
shown. The INT output is identical to STAT and is used to interface with a low voltage host processor.
Table 1. STAT Pin Summary
Charge State
Charge in progress and EN_STAT=1
Other normal conditions
Status Changes: Supply Status Change (plug in or removal), safety timer fault,
watchdog expiration, sleep mode, battery temperature fault (TS), battery fault (OVP or
absent), thermal shutdown
STAT and INT behavior
Low
High-Impedance
128-µs pulse, then High Impedance
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