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PRE-CHARGE TIMER
THERMAL PROTECTION LOOP
THERMAL SHUTDOWN AND PROTECTION
bq2406x
SLUS689A – JUNE 2006 – REVISED OCTOBER 2006
The bq2406x 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 .
Table 4. Pre-Charge Timer Operational Modes
bq2460X MODE V(OUT) > V
(LOWV)
PRE-CHARGE TIMER MODE
STANDBY ( CE = Hi) X RESET
CHARGING Yes RESET
SUSPEND (TS out of range) Yes RESET
SUSPEND (TS out of range) No Hold
CHARGING, TMR PIN NOT OPEN No COUNTING, EXTERNAL PROGRAMMED RATE
CHARGING, TMR PIN OPEN X 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 FAULT LATCH RESET AT
CE rising edge or OVP detected
Pre-charge timer timeout AND V(OUT) > V
(LOW V)
Input power removed (not detected)
Timer function disabled
An internal control loop monitors the bq2406x junction termperature (T
J
) to ensure safe operation during high
power dissipations and or increased ambient temperatures. This loop monitors the bq2406x junction
temperature and reduces the charge current as necessary to keep the junction temperature from exceeding,
T
J(REG)
, (112 ° C, typical).
The bq2406x's thermal loop control can reduce the charging current down to ~200mA if needed. If the junction
temperature continues to rise, the IC will enter thermal shutdown.
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
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