BQ24618_15 Datasheet, PDF (18/43 Pages) Texas Instruments – System Power Selector and Low

bq24618
SLUSA55B – OCTOBER 2010 – REVISED APRIL 2015
www.ti.com
Feature Description (continued)
8.3.5 Charge Termination, Recharge, and Safety Timer
The bq24618 monitors the charging current during the voltage regulation phase. When V_TTC is valid, termination
is detected while the voltage on the VFB pin is higher than the V_RECH threshold AND the charge current is less
than the I_TERM threshold, as calculated in Equation 5:
I_TERM =
V_ISET2
100 ´ R_SR
(5)
The input voltage of ISET2 is from 0 V to 2 V. The minimum precharge and termination current is clamped to be
around 125 mA with default 10-mΩ sensing resistor. As a safety backup, the bq24618 also provides a
programmable charge timer. The charge time is programmed by the capacitor connected between the TTC pin
and GND, and is given by Equation 6
t_CHARGE = C_TTC ´ K_TTC
where
• C_TTC (range from 0.01 µF to 0.11 µF to give 1-h to 10-h safety time) is the capacitor connected from the TTC
pin to GND.
• K_TTC is the constant multiplier (5.6 min/nF).
(6)
A new charge cycle is initiated and the safety timer is reset when any of the following conditions occurs:
• The battery voltage falls below the recharge threshold.
• A power-on-reset (POR) event occurs.
• CE is toggled.
The TTC pin may be taken LOW to disable termination and to disable the safety timer. If TTC is pulled to VREF,
the bq24618 continues to allow termination but disable the safety timer. TTC taken low resets the safety timer.
When ACOV, VCCLOWV, and SLEEP mode resume normal, the safety timer is reset.
8.3.6 Power Up
The bq24618 uses a SLEEP comparator to determine the source of power on the VCC pin, because VCC can be
supplied either from the battery or the adapter. If the VCC voltage is greater than the SRN voltage, the bq24618
enables the ACFET and disables BATFET. If all other conditions are met for charging, the bq24618 then
attempts to charge the battery (see Enable and Disable Charging). If the SRN voltage is greater than VCC,
indicating that the battery is the power source, the bq24618 enables the BATFET and enters a low quiescent
current (<15-μA) SLEEP mode to minimize current drain from the battery.
If VCC is below the UVLO threshold, the device is disabled, ACFET turns off, and BATFET turns on.
8.3.7 Enable and Disable Charging
The following conditions must be valid before charge is enabled:
• CE is HIGH.
• The device is not in UVLO and not in VCCLOWV mode.
• The device is not in SLEEP mode.
• The VCC voltage is lower than the AC overvoltage threshold (VCC < V_ACOV).
• 30-ms delay is complete after initial power up.
• The REGN LDO and VREF LDO voltages are at the correct levels.
• Thermal shutdown (TSHUT) is not valid.
• TS fault is not detected.
Any of the following conditions will stop ongoing charging:
• CE is LOW.
• Adapter is removed, causing the device to enter UVLO, VCCLOWV, or SLEEP mode.
• Adapter is over voltage.
• The REGN or VREF LDOs are overloaded.
• TSHUT IC temperature threshold is reached (145°C on rising edge with 15°C hysteresis).
18
Submit Documentation Feedback
Product Folder Links: bq24618
Copyright © 2010–2015, Texas Instruments Incorporated