Datasheet

ISET
TERM
SR
V
I =
200 R´
bq24620
www.ti.com SLUS893A –MARCH 2010– REVISED OCTOBER 2011
PRECHARGE
On power up, if the battery voltage is below the V
LOWV
threshold, the bq24620 applies 125 mA to the battery.
(1)
The precharge feature is intended to revive deeply discharged cells. If the V
LOWV
threshold is not reached within
30 minutes of initiating precharge, the charger turns off and a FAULT is indicated on the status pins.
CHARGE TERMINATION, RECHARGE, AND SAFETY TIMER
The bq24620 monitors the charging current during the voltage regulation phase. 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, which is 1/10
th
of programmed charge current, as calculated in Equation 3:
(3)
As a safety backup, the bq24620 also provides an internal 5-hour charge timer for fast charge.
A new charge cycle is initiated when one of the following conditions occurs:
• The battery voltage falls below the recharge threshold.
• A power-on-reset (POR) event occurs.
• CE is toggled.
POWER UP
The bq24620 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 bq24620
enables ACFET and disables BATFET. If all other conditions are met for charging, the bq24620 then attempts to
charge the battery (see Enable and Disabe Charging, ENABLE AND DISABLE CHARGING). If the SRN voltage
is greater than VCC, indicating that the battery is the power source, bq24620 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.
ENABLE AND DISABLE CHARGING
The following conditions must be valid before charge is enabled:
• CE is HIGH.
• The device is not in VCCLOWV mode.
• The device is not in SLEEP mode (i.e., VCC > SRN) .
• 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 shut (TSHUT) is not valid.
• TS fault is not detected.
Any of the following conditions stops ongoing charging:
• CE is LOW.
• Adapter is removed, causing the device to enter VCCLOWV or SLEEP mode.
• Adapter voltage is less than 100mV above battery.
• 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).
• TS voltage goes out of range, indicating the battery temperature is too hot or too cold.
• Safety timer times out.
(1) 125 mA (assuming a 10-mΩ sense resistor. 1.25 mV is regulated across SRP-SRN, regardless of the value of the sense resistor.)
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