BQ24030-Q1 Datasheet, PDF (21/34 Pages) Texas Instruments – SINGLE-CHIP CHARGE AND SYSTEM POWER-PATH MANAGEMENT IC

bq24030-Q1
bq24031-Q1
www.ti.com.................................................................................................................................................... SLUS793B – APRIL 2008 – REVISED OCTOBER 2009
If this is a concern, there is a simple external solution. Externally toggling the PSEL pin immediately starts the
power-transfer process (does not wait for input to drop to the battery's voltage). This can 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 + 90 kΩ(30 kΩ + 280 kΩ)/(280 kΩ × 30 kΩ) = 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 V_BAT)
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 series features a junction temperature regulation loop. If the
power dissipation of the bqTINY III series results in a junction temperature greater than the T_J(REG) threshold
(125°C, typical), the bqTINY III series throttles back on the charge current in order 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 reduced charge current results in a longer charge time so the safety timer, t_(CHG) is
extended inversely. This means that if the temperature regulation loop reduces the current to half of the
programmed charge rate, then the safety timer t_(CHG) doubles. See Charge Timer Operation for more detail.
The bqTINY III series also monitors the junction temperature, T_J, of the die and disconnects the OUT pin from
AC or USB inputs 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.
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 series monitors the charge time in the charge mode. If the termination
threshold is not detected within the time period, t_(CHG), the bqTINY III series 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 LDO pin. Note that this action eliminates the fast-charge
safety timer (does not disable or reset the pre-charge safety timer), disables termination, and also clears a
fast-charge timer fault. TMR pin should not be left floating.
t_(CHG) + K_(TMR) R_(TMR)
(6)
While in the thermal regulation mode or DPPM mode, the bqTINY III series 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 7.
t _{(CHG−TREG)}
+
t_(CHG) V_(SET)
V_(SET*REG)
(7)
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.)
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