BQ24085 Datasheet, PDF (18/34 Pages) Texas Instruments – 750 mA SINGLE-CHIP Li-Ion/Li-Pol CHARGE MANAGEMENT IC WITH THERMAL REGULATION

bq24085, bq24086
bq24087, bq24088
SLUS784B – DECEMBER 2007 – REVISED MAY 2008 .................................................................................................................................................... www.ti.com
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)
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 (i.e., pre-charge timer is not reset), 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 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 those 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
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 or 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 ~105 mA if needed. If the
junction temperature continues to rise, the IC will enter thermal shutdown.
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.
18
Submit Documentation Feedback
Copyright © 2007–2008, Texas Instruments Incorporated
Product Folder Link(s): bq24085, bq24086 bq24087, bq24088