BQ29312_15 Datasheet, PDF (14/39 Pages) Texas Instruments – FOUR CELL LITHIUM-ION

bq29312
SLUS546E – MARCH 2003 – REVISED MARCH 2005
www.ti.com
FUNCTIONAL DESCRIPTION (continued)
Watchdog Input (WDI)
The WDI input is required as a time base for delay timing when determining overload and short-circuit delay
periods and is used as part of the system watchdog.
Initially the watchdog monitors the hosts oscillator start up, if there is no response from the host within 700 ms of
the bq29312 reaching its minimum operating voltage, then the bq29312 turns both CHG, DSG and ZVCHG FETs
OFF.
Once the watchdog has been started during this wake up period, it monitors the host for an oscillation stop
condition, which is defined as a period of 100 µs (typ) where no clock input is received. If an oscillator stop
condition is identified, then the watchdog turns the CHG, DSG and ZVCHG FETs OFF. When the host clock
oscillation is started, WDF is released, but the flag is latched until LTCLR is toggled.
REG
GG 32 kHz Output
GG Clock Never Starts
t_WDTINT ∼ 700 mS
EXT FET Control
CHG, DSG and
ZVCHG = OFF
Figure 2. Watchdog Timing Chart—WDI Fault at Startup
REG
GG 32 kHz Output
GG Clock Stop
Watchdog Sense
EXT FET Control
t_WDWT About 100 µS
Figure 3. Watchdog Timing Chart—WDI Fault After Startup
CHG, DSG and
ZVCHG = OFF
DSG and CHG FET Driver Control
The bq29312 drives the DSG, CHG, and ZVCHG FET off if an OL or SC safety threshold is breached depending
on the current direction. The host can force any FET on or off only if the bq29312 integrated protection control
allows. The DSG and CHG FET drive gate-to-drain voltage is clamped to 15 V (typ).
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