BQ24070_14 Datasheet, PDF (18/33 Pages) Texas Instruments – System Power-Path Management IC

bq24070, bq24071
SLUS694G – MARCH 2006 – REVISED DECEMBER 2014
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.
8.4.3.7 Charge Timer Operation
As a safety backup, the bq2407x monitors the charge time in the charge mode. If the termination threshold is not
detected within the time period, t_(CHG), the bq2407x 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 precharge 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 bq2407x 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 deglitch times also adjusted proportionally to t_(CHG-TREG).
8.4.3.8 Timer Fault Recovery
As shown in Figure 6, bq2407x provides a recovery method to deal with timer fault conditions. The following
summarizes this method:
Condition 1: Charge voltage above recharge threshold (V_(RCH)) and time-out fault occurs.
Recovery Method: bq2407x waits for the battery voltage to fall below the recharge threshold. This could happen
as a result of a load on the battery, self-discharge, or battery removal. Once the battery falls below the recharge
threshold, the bq2407x clears the fault and starts a new charge cycle. A POR or CE toggle also clears the fault.
Condition 2: Charge voltage below recharge threshold (V_(RCH)) and time-out fault occurs.
Recovery Method: Under this scenario, the bq2407x applies the I_(FAULT) current. This small current is used to
detect a battery removal condition and remains on as long as the battery voltage stays below the recharge
threshold. If the battery voltage goes above the recharge threshold, then the bq2407x disables the I_(FAULT) current
and executes the recovery method described for condition 1. Once the battery falls below the recharge threshold,
the bq2407x clears the fault and starts a new charge cycle. A POR or CE toggle also clears the fault.
18
Submit Documentation Feedback
Copyright © 2006–2014, Texas Instruments Incorporated
Product Folder Links: bq24070 bq24071