BQ24620 Datasheet, PDF (15/30 Pages) Texas Instruments – Stand-Alone Synchronous Switch-Mode Lithium Phosphate Battery Charger with Low Iq

bq24620
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SLUS893 – MARCH 2010
PRECHARGE
On power-up, if the battery voltage is below the V_LOWV threshold, the bq24620 applies 125mA 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:
I_TERM =
V_ISET
200 ´ R_SR
(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 occur:
• 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, since VCC can be
supplied either from the battery or the adapter. If the VCC voltage is greater than the SRN voltage, bq24620 will
enable the ACFET and disable BATFET. If all other conditions are met for charging, bq24620 will then attempt to
charge the battery (See Enabling and Disabling Charging). If the SRN voltage is greater than VCC, indicating
that the battery is the power source, bq24620 enters a low quiescent current (<15mA) 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 have to 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 over-voltage 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.
One of the following conditions will stop on-going 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) 125mA (assuming a 10mΩ sense resistor. 1.25mV will be regulated across SRP-SRN, regardless of the value of the sense resistor.)
Copyright © 2010, Texas Instruments Incorporated
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