BQ24070_14 Datasheet, PDF (17/33 Pages) Texas Instruments – System Power-Path Management IC

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bq24070, bq24071
SLUS694G – MARCH 2006 – REVISED DECEMBER 2014
8.4.3.3 Battery Preconditioning
During a charge cycle, if the battery voltage is below the V_(LOWV) threshold, the bq2407x applies a precharge
current, I_O(PRECHG), to the battery. This feature revives deeply discharged cells. The R_SET resistor, connected
between the ISET1 and VSS pins, determines the precharge rate. The V_(PRECHG) and K_(SET) parameters are
specified in the specifications table. Note that this applies to both IN-mode and USB-mode charging.
I_{O (PRECHG)} =
V_{(PRECHG) ×}
R_SET
K_(SET)
(3)
The bq2407x activates a safety timer, t_(PRECHG), during the conditioning phase. If V_(LOWV) threshold is not reached
within the timer period, the bq2407x turns off the charger and enunciates FAULT on the STAT1 and STAT2 pins.
The time-out is extended if the charge current is reduced by DPPM or thermal regulation. See the Timer Fault
Recovery section for additional details.
8.4.3.4 Battery Charge Current
The bq2407x offers on-chip current regulation with programmable set point. The R_SET resistor, connected
between the ISET1 and VSS pins, determines the charge level. The charge level may be reduced to give the
system priority on input current (see DPPM). The V_(SET) and K_(SET) parameters are specified in the specifications
table.
I_{O (OUT)}
=
V_{(SET) ×} K_(SET)
R_SET
(4)
When powered from a USB port, the input current available (0.1 A/0.5 A) is typically less than the programmed
(ISET1) charging current, and therefore, the DPPM feature attempts to keep the output from being pulled down
by reducing the charging current.
The charge level, during IN mode operation only (Mode = High), can be changed by a factor of 2 by setting the
ISET2 pin high (full charge) or low (half charge). The voltage on the ISET1 pin, VSET1, is divided by 2 when in
the half constant current charge mode. Note that with Mode low, the ISET2 pin controls only the 0.1 A/0.5 A USB
current level.
See Power-Path Management for additional details.
8.4.3.5 Battery Voltage Regulation
The voltage regulation feedback is through the BAT pin. This input is tied directly to the positive side of the
battery pack. The bq2407x monitors the battery-pack voltage between the BAT and VSS pins. When the battery
voltage rises to the V_O(REG) threshold, the voltage regulation phase begins and the charging current begins to
taper down.
If the battery is absent, the BAT pin cycles between charge done (V_O(REG)) and charging (battery recharge
threshold, approximately 4.1 V).
See Figure 8 for power up by battery insertion.
As a safety backup, the bq2407x also monitors the charge time in the charge mode. If charge is not terminated
within this time period, t_(CHG), the bq2407x turns off the charger and enunciates FAULT on the STAT1 and
STAT2 pins. See the DPPM operation under Case 1 for information on extending the safety timer during DPPM
operation. See the Timer Fault Recovery section for additional details.
8.4.3.6 Temperature Regulation and Thermal Protection
To maximize charge rate, the bq2407x features a junction temperature regulation loop. If the power dissipation of
the IC results in a junction temperature greater than the T_J(REG) threshold, the bq2407x throttles back on the
charge current to maintain a junction temperature around the T_J(REG) threshold. To avoid false termination, the
termination detect function is disabled while in this mode.
The bq2407x also monitors the junction temperature, T_J, of the die and disconnects the OUT pin from the IN
input if T_J exceeds T_(SHTDWN). This operation continues until T_J falls below T_(SHTDWN) by the hysteresis level
specified in the specification table.
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Product Folder Links: bq24070 bq24071
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