bq24030, bq24031, bq24032,
bq24032A, bq24035, bq24038, bq24039
www.ti.com
SLUS618C–AUGUST 2004–REVISED JUNE 2005
be implemented by a resistor divider between the AC input and ground with the PSEL pin tied between R1 (top
resistor) and R2 (resistor to ground). The resistor values are chosen such that the divider voltage will be at 1 V
(PSEL threshold) when the AC has dropped to its critical voltage (user defined). An internal ~280-kΩ resistor is
applied when PSEL < 1 V, to provide hysteresis. Choose R2 between 10 kΩ and 60 kΩ and V(ac-critical) between
3.5 V and 4.5 V. R1 can be found using the following equation:
R1 = R2 (V(ac-critical) – 1 V); V(ac-reset) = 1 + R1 (R2+280 k)/(280 k × R2);
Example: If R2 = 30 kΩ and V(ac-critical) = 4 V; R1 = 30 kΩ(4 V – 1 V) = 90 kΩ, V(ac-reset) = 1+ 90k (30 k+280
k)/(280 k×30 k) = 4.32 V. Therefore, for a 90 kΩ/30 kΩ divider, the bias on PSEL would switch power from AC to
USB (USBPG = L) when the VAC dropped to 4 V (independent of VBAT) and switches back when the VAC
recovers to 4.32 V. See Figure 6 through Figure 10.
Temperature Regulation and Thermal Protection
In order to maximize charge rate, the bqTINY-III features a junction temperature regulation loop. If the power
dissipation of the IC results in a junction temperature greater than the TJ(REG) threshold, the bqTINY-III throttles
back on the charge current in order to maintain a junction temperature around the TJ(REG) threshold. To avoid
false termination, the termination detect function is disabled while in this mode.
The bqTINY-III also monitors the junction temperature, TJ, of the die and disconnects the OUT pin from AC or
USB inputs if TJ exceeds T(SHTDWN). This operation continues until TJ falls below T(SHTDWN) by the hysteresis level
specified in the specification table.
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 bqTINY-III monitors the charge time in the charge mode. If the termination threshold is
not detected within the time period, t(CHG), the bqTINY-III turns off the charger and enunciates FAULT on the
STAT1 and STAT2 pins. The resistor connected between the TMR and VSS, RTMR, determines the timer period.
The K(TMR) parameter is specified in the specifications table. In order to disable the charge timer, eliminate RTMR
,
connect the TMR pin directly to the LDO pin. Note that this action eliminates all safety timers, disables
termination, and also clears any timer fault. TMR pin should not be left floating.
t
K
R
(CHG)
(TMR)
(TMR)
(5)
While in the thermal regulation mode or DPPM mode, the bqTINY-III 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
V
(CHG)
(SET)
t
+
(CHG*TREG)
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.)
I
R
(OUT)
(SET)
V
+
(SET*TREG)
K
(SET)
(7)
All deglitch times also adjusted proportionally to t(CHG-TREG)
.
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