BQ24085_17 Datasheet, PDF (17/42 Pages) Texas Instruments – 750-mA Single-Chip Li-Ion and Li-Pol Charge Management IC With Thermal Regulation

www.ti.com
bq24085, bq24086, bq24087, bq24088
SLUS784E – DECEMBER 2007 – REVISED DECEMBER 2015
8.3.8 Pre-Charge Timer
The bq24085/6/7/8 family activates an internal safety timer during the battery pre-conditioning phase. The charge
safety timer time-out value is set by the external resistor connected to TMR pin, R_TMR, and the timeout constants
K_(PCHG) and t_(CHG) :
t_(PCHG) = K_(PCHG) × t_(CHG)
(6)
The pre-charge timer operation is detailed in Table 4.
bq24085/6/7/8 MODE
STANDBY (CE = Hi)
CHARGING
SUSPEND (TS out of range)
SUSPEND (TS out of range)
CHARGING, TMR PIN NOT OPEN
CHARGING, TMR PIN OPEN
Table 4. Pre-Charge Timer Operational Modes
V(OUT) > V_(LOWV)
X
Yes
Yes
No
No
X
PRE-CHARGE TIMER MODE
RESET
RESET
RESET
Hold
COUNTING, EXTERNAL PROGRAMMED RATE
RESET
In SUSPEND mode the pre-charge timer is put on hold (that is, pre-charge timer is not reset). Once normal
operation resumes when the timer returns to the normal operating mode (COUNTING). If V_(BAT) does not reach
the internal voltage threshold V_(LOWV) within the pre-charge timer period, a fault condition is detected. The
charger is then turned off, and the pre-charge safety timer fault condition is latched.
When the pre-charge timer fault latch is set the charger is turned off. Under these conditions a small current
I_FAULT is applied to the OUT pin, as long as input power (IN) is detected AND V_(OUT) < V_(LOWV), as part of a timer
fault recovery protocol. This current allows the output voltage to rise above the pre-charge threshold V_(LOWV),
resetting the pre-charge timer fault latch when the pack is removed. Table 5 further details the pre-charge timer
fault latch operation.
Table 5. Pre-Charge Timer Latch Functionality
PRE-CHARGE TIMER FAULT ENTERED WHEN
Pre-charge timer timeout AND V_(OUT) < V_{(LOW V)}
PRE-CHARGE TIMER FAULT LATCH RESET AT
CE rising edge or OVP detected
Input power removed (not detected)
Timer function disabled
8.3.9 Thermal Protection Loop
An internal control loop monitors the bq24085/6/7/8 junction temperature (T_J) to ensure safe operation during
high power dissipations and increased ambient temperatures. This loop monitors the bq24085/6/7/8 junction
temperature and reduces the charge current as necessary to keep the junction temperature from exceeding,
T_J(REG), (112°C, typical).
The bq24085/6/7/8's thermal loop control can reduce the charging current down to approximately 105 mA if
needed. If the junction temperature continues to rise, the IC will enter thermal shutdown.
8.3.10 Thermal Shutdown And Protection
Internal circuits monitor the junction temperature, T_J, of the die and suspends charging if T_J exceeds an internal
threshold T_(SHUT) (155°C typical). Charging resumes when T_J falls below the internal threshold T_(SHUT) by
approximately 20°C.
8.3.11 Dynamic Timer Function
The charge and pre-charge safety timers are programmed by the user to detect a fault condition if the charge
cycle duration exceeds the total time expected under normal conditions. The expected charge time is usually
calculated based on the fast charge current rate.
When the thermal loop is activated the charge current is reduced, and bq24085/6/7/8 activates the dynamic timer
control. The dynamic timer control is an internal circuit that slows down the safety timer's clock frequency. The
dynamic timer control circuit effectively extends the safety time duration for either the precharge or fast charge
timer modes. This minimizes the chance of a safety timer fault due to thermal regulation.
Copyright © 2007–2015, Texas Instruments Incorporated
Submit Documentation Feedback
17
Product Folder Links: bq24085 bq24086 bq24087 bq24088