BQ24171_15 Datasheet, PDF (18/39 Pages) Texas Instruments – bq24171 JEITA-Compliant Stand-Alone, Switched-Mode Li-Ion and Li-Polymer Battery Charger With Integrated MOSFETs and Power Path Selector

bq24171
SLUSAF2C – FEBRUARY 2011 – REVISED APRIL 2015
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Feature Description (continued)
Pull the TTC pin to AGND to disable both termination and fast charge safety timer (reset timer). Pull the TTC pin
to VREF to disable the safety timer, but allow charge termination.
9.3.6 Power Up
The charge uses a SLEEP comparator to determine the source of power on the AVCC pin because AVCC can
be supplied either from the battery or the adapter. With the adapter source present, if the AVCC voltage is
greater than the SRN voltage, the charger exits SLEEP mode. If all conditions are met for charging, the charger
then starts charge the battery (see Enable and Disable Charging). If SRN voltage is greater than AVCC, the
charger enters low quiescent current SLEEP mode to minimize current drain from the battery. During SLEEP
mode, the VREF output turns off and the STAT pin goes to high impedance.
If AVCC is below the UVLO threshold, the device is disabled.
9.3.7 Input Undervoltage Lockout (UVLO)
The system must have a minimum AVCC voltage to allow proper operation. This AVCC voltage could come from
either input adapter or battery because a conduction path exists from the battery to AVCC through the high-side
NMOS body diode. When AVCC is below the UVLO threshold, all circuits on the IC are disabled.
9.3.8 Input Overvoltage/Undervoltage Protection
ACOV provides protection to prevent system damage due to high input voltage. In bq24171, once the voltage on
OVPSET is above the 1.6-V ACOV threshold or below the 0.5-V ACUV threshold, charge is disabled and input
MOSFETs turn off. The bq24171 provides flexibility to set the input qualification threshold.
9.3.9 Enable and Disable Charging
The following conditions have to be valid before charging is enabled:
• ISET pin above 120 mV.
• Device is not in UVLO mode (that is, V_AVCC > V_UVLO).
• Device is not in SLEEP mode (that is, V_AVCC > V_SRN).
• OVPSET voltage is from 0.5 V to 1.6 V to qualify the adapter.
• 1.5-s delay is complete after initial power up.
• REGN LDO and VREF LDO voltages are at correct levels.
• Thermal Shutdown (TSHUT) is not valid.
• TS fault is not detected.
• ACFET turns on (see System Power Selector for details).
One of the following conditions stops ongoing charging:
• ISET pin voltage is below 40 mV.
• Device is in UVLO mode.
• Adapter is removed, causing the device to enter SLEEP mode.
• OVPSET voltage indicates the adapter is not valid.
• REGN or VREF LDO voltage is overloaded.
• TSHUT temperature threshold is reached.
• TS voltage goes out of range, indicating the battery temperature is too hot or too cold.
• ACFET turns off.
• TTC timer expires or precharge timer expires.
9.3.10 System Power Selector
The IC automatically switches adapter or battery power to the system load. The battery is connected to the
system by default during power up or during SLEEP mode. When the adapter plugs in and the voltage is above
the battery voltage, the IC exits SLEEP mode. The battery is disconnected from the system and the adapter is
connected to the system after exiting SLEEP. An automatic break-before-make logic prevents shoot-through
currents when the selectors switch.
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