Data Sheet

bq24072 , bq24073 , bq24074 , bq24075 , bq24079
SLUS810K –SEPTEMBER 2008–REVISED MARCH 2015 www.ti.com
Feature Description (continued)
• The system load current activates the DPPM loop which reduces the available charging current
• The input current is reduced because the input voltage has fallen to V
IN(LOW)
• The device has entered thermal regulation because the IC junction temperature has exceeded T
J(REG)
During each of these events, the internal timers are slowed down proportionately to the reduction in charging
current. For example, if the charging current is reduced by half for two minutes, the timer clock is reduced to half
the frequency and the counter counts half as fast resulting in only one minute of "counting" time.
If the pre charge timer expires before the battery voltage reaches V
LOWV
, the bq2407x indicates a fault condition.
Additionally, if the battery current does not fall to I
TERM
before the fast charge timer expires, a fault is indicated.
The CHG output flashes at approximately 2 Hz to indicate a fault condition. The fault condition is cleared by
toggling CE or the input power, entering/ exiting USB suspend mode, or an OVP event.
9.3.5.7 Status Indicators (PGOOD, CHG)
The bq2407x contains two open-drain outputs that signal its status. The PGOOD output signals when a valid
input source is connected. PGOOD is low when (V
BAT
+ V
IN(DT)
) < V
IN
< V
OVP
. When the input voltage is outside
of this range, PGOOD is high impedance.
The charge cycle after power-up, CE going low, or exiting OVP is indicated with the CHG pin on (low - LED on),
whereas all refresh (subsequent) charges will result in the CHG pin off (open - LED off). In addition, the CHG
signals timer faults by flashing at approximately 2 Hz.
Table 1. PGOOD Status Indicator
INPUT STATE PGOOD OUTPUT
V
IN
< V
UVLO
High-impedance
V
UVLO
< V
IN
< V
IN(DT)
High-impedance
V
IN(DT)
< V
IN
< V
OVP
Low
V
IN
> V
OVP
High-impedance
Table 2. CHG Status Indicator
CHARGE STATE CHG OUTPUT
Charging
Low (for first charge cycle)
Charging suspended
by thermal loop
Safety timers expired Flashing at 2 Hz
Charging done
Recharging after
termination
High-impedance
IC disabled or no valid
input power
Battery absent
9.3.5.8 Thermal Regulation and Thermal Shutdown
The bq2407x contain a thermal regulation loop that monitors the die temperature. If the temperature exceeds
T
J(REG)
, the device automatically reduces the charging current to prevent the die temperature from increasing
further. In some cases, the die temperature continues to rise despite the operation of the thermal loop,
particularly under high VIN and heavy OUT system load conditions. Under these conditions, if the die
temperature increases to T
J(OFF)
, the input FET Q1 is turned OFF. FET Q2 is turned ON to ensure that the
battery still powers the load on OUT. Once the device die temperature cools by T
J(OFF-HYS)
, the input FET Q1 is
turned on and the device returns to thermal regulation. Continuous overtemperature conditions result in a
"hiccup" mode. During thermal regulation, the safety timers are slowed down proportionately to the reduction in
current limit.
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