BQ24070RHLRG4 Datasheet, PDF (18/31 Pages) Texas Instruments – SINGLE-CHIP LI-ION CHARGE AND SYSTEM POWER-PATH MANAGEMENT IC

bq24070
bq24071
SLUS694F – MARCH 2006 – REVISED DECEMBER 2009
www.ti.com
The battery supplement mode has no thermal protection. The Q2 FET continues to connect the battery to the
output (system), if input power is not sufficient; however, a short-circuit protection circuit limits the battery
discharge current such that the maximum power dissipation of the part is not exceeded under typical design
conditions.
Charge Timer Operation
As a safety backup, the bq24070/1 monitors the charge time in the charge mode. If the termination threshold is
not detected within the time period, t_(CHG), the bq24070/1 turns off the charger and enunciates FAULT on the
STAT1 and STAT2 pins. The resistor connected between the TMR and VSS, R_TMR, determines the timer period.
The K_(TMR) parameter is specified in the specifications table. In order to disable the charge timer, eliminate R_TMR,
connect the TMR pin directly to the V_REF pin. Note that this action eliminates the fast-charge safety timer (it does
not disable or reset the pre-charge safety timer), and also clears any timer fault. TMR pin should not be left
floating.
t_(CHG) + K_(TMR) R_(TMR)
(5)
While in the thermal regulation mode or DPPM mode, the bq24070/1 dynamically adjusts the timer period in
order to provide the additional time needed to fully charge the battery. This proprietary feature is designed to
prevent against early or false termination. The maximum charge time in this mode, t_(CHG-TREG), is calculated by
Equation 6.
t _{(CHG−TREG)}
+
t_(CHG) V_(SET)
V_(SET*REG)
(6)
Note that because this adjustment is dynamic and changes as the ambient temperature changes and the charge
level changes, the timer clock is adjusted. It is difficult to estimate a total safety time without integrating the
above equation over the charge cycle. Therefore, understanding the theory that the safety time is adjusted
inversely proportionately with the charge current and the battery is a current-hour rating, the safety time
dynamically adjusts appropriately.
The V_(SET) parameter is specified in the specifications table. V_(SET-TREG) is the voltage on the ISET pin during the
thermal regulation or DPPM mode and is a function of charge current. (Note that charge current is dynamically
adjusted during the thermal regulation or DPPM mode.)
V_{(SET−TREG)}
+
I_(OUT) R_(SET)
K_(SET)
(7)
All de-glitch times also adjusted proportionally to t_(CHG-TREG).
Charge Termination and Recharge
The bq24070/1 monitors the voltage on the ISET1 pin, during voltage regulation, to determine when termination
should occur. Termination occurs when the charge current tapers down to either 1/10^th of the programmed fast
charge rate (when the MODE pin is high) or 1/25^th of the programmed fast charge rate (when the MODE pin is
low). Once the termination threshold, I_(TERM), is detected the bq24070/1 terminates charge. The R_SET resistor,
connected between the ISET1 and VSS pins, programs the fast charge current level and thus the current
termination threshold level. The V_(TERM) and K_(SET) parameters are specified in the specifications table. Note that
this applies to both AC and USB charging.
I_(TERM)
+
V_(TERM) K_(SET)
R_SET
(8)
After charge termination, the bq24070/1 re-starts the charge once the voltage on the BAT pin falls below the
V_(RCH) threshold. This feature keeps the battery at full capacity at all times.
Sleep and Standby Modes
The bq24070/1 charger circuitry enters the low-power sleep mode if the input is removed from the circuit. This
feature prevents draining the battery into the bq24070/1 during the absence of input supply. Note that in sleep
mode, Q2 remains on (i.e., battery connected to the OUT pin) in order for the battery to continue supplying power
to the system.
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