BQ26501_16 Datasheet, PDF (22/33 Pages) Texas Instruments – HANDHELD APPLICATIONS

bq26501
Not Recommended For New Designs
ą
SLUS586B − OCTOBER 2003 − REVISED MARCH 2004
APPLICATION INFORMATION
Active Mode
During normal operation, the device is in active mode, which corresponds to the highest power consumption.
Normal gas gauging is performed in this mode. If system requirements mandate that bq26501 should not enter
sleep or ship modes then an external pull-up resistor between V_CC and HDQ is required on the bq26501 side
of the system. The resistor value chosen should be small enough to force a logic “1” on HDQ even with the HDQ
internal pull-down current and any external ESD protection circuitry loading.
Sleep Mode
This low power mode is entered when the HDQ line is pulled low for at least 16 seconds and the charge or
discharge activity is below the digital magnitude filter. It may take up to 30 minutes to determine the no-activity
condition after charge or discharge current is removed. Normal gas gauging ceases, but battery self-discharge,
based on the temperature when the device entered sleep mode, is maintained internally. The device wakes
every 4 hours to perform a temperature conversion and will go back to sleep after 16 seconds if the HDQ line
is still low. bq26501 has an internal pull-down device that sinks less than I_HDQPD, allowing the device to enter
sleep mode if the battery pack is pulled from the system and there is not a pull-up mechanism present.
When the device wakes the first time to perform a temperature update, it stays in active mode long enough to
confirm that the charge or discharge activity is still below the digital magnitude filter threshold. This is meant
to minimize possible error if the battery pack is removed from the end equipment and is later re-inserted without
a transition on the HDQ line. This is only an issue if the system has some current drain from the battery even
though HDQ is pulled low. The activity check will take 15 minutes to complete. The device reenters sleep mode
if the activity is below the digital magnitude filter threshold. The device repeats the activity check every 3
wakeups (12 hours).
When the HDQ line is pulled high, the device leaves the sleep mode. The device enters the sleep mode again
only after the HDQ line is pulled low for at least 16 seconds and the charge/discharge activity is below the digital
magnitude filter threshold. If the DMF threshold is set to zero and HDQ line is pulled low, the device enters sleep
mode if the VFC activity is less than 2 counts in 15 minutes. This is equivalent to approximately 24 µV across
the current-sense resistor.
A 100-kΩ pull-up resistor from HDQ to V_CC can be added in the battery pack to disable the sleep function.
Ship Mode
This low power mode is to be used when the pack manufacturer has completed assembly and test of the pack.
The ship mode is enabled by setting the SHIP bit in the MODE register and issuing the control command (data
0xA9 to register 0x00). Ship mode is entered only after the ship mode is enabled and the HDQ line has been
pulled low for 16 seconds. This allows the pack manufacturer to enable the ship mode and pull the pack from
the test equipment without any additional overhead. After the ship mode has been enabled but before the device
has entered ship mode, transients on the HDQ line do not cause the device to stay in active mode.
All device functionality stops in ship mode and it does not start again until the HDQ line is pulled high (by plugging
it into the end equipment) or the battery voltage drops below and then rises above the V_(POR) threshold. Care
should be taken to ensure that there are no glitches on the HDQ line after the device enters ship mode or else
the device enters the active mode. It enters sleep if HDQ remains low, but does not re-enter ship mode unless
another ship mode command is sent.
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