Not Recommended for New Designs

bq28550-R1

SLUSAS4A – OCTOBER 2012 – REVISED SEPTEMBER 2014

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mode until it has taken a valid OCV measurement and the magnitude of the average cell current has fallen

below Hibernate Current.

•

HIBERNATE due to the cell voltage—When the cell voltage drops below the Hibernate Voltage and a valid

OCV measurement has been taken, the gas gauge enters HIBERNATE mode. The [HIBERNATE] bit of the

CONTROL register has no impact for the gas gauge to enter the HIBERNATE mode. If the [SHUTDOWN] bit

of CONTROL _STATUS is also set.

The gauge will remain in HIBERNATE mode until communication activity appears on the communication lines.

Upon exiting HIBERNATE mode, the [HIBERNATE] bit of CONTROL_STATUS is cleared.

Because the gas gauge is dormant in HIBERNATE mode, the battery should not be charged or discharged in this

mode, because any changes in battery charge status will not be measured. If necessary, the host equipment can

draw a small current (generally infrequent and less than 1 mA, for purposes of low-level monitoring and

updating); however, the corresponding charge drawn from the battery will not be logged by the gauge. Once the

gauge exits to NORMAL mode, the algorithm re-establishes the correct battery capacity.

If a charger is attached, the host should immediately take the gas gauge out of HIBERNATE mode before

beginning to charge the battery.

CAUTION

Charging the battery in HIBERNATE mode results in a notable gauging error that will

take several hours to correct.

7.6.5.5 SHUTDOWN Mode

The device enters SHUTDOWN mode if there is a UVP condition detected or if there is a power down of the

system, and alternatively by setting the SHUTRQ bit to 1, if appropriate conditions are met. The device can also

disable SHUTDOWN by using the CLEAR_SHUTDOWN (0x0014) option.

NOTE

•

A SHUTDOWN command should NOT be invoked if charger voltage is present.

•

Sending a SHUTDOWN command while charger voltage is present causes a 1–2 s

time of DSG FET off, and may or may not cause a watchdog reset. (If current is

≤ 0

after the DSG FET is opened, it will attempt to shutdown and start a watchdog;

otherwise, it will only clear the shutdown flag without a reset).

Figure 4 shows an overview of the hardware controlled SHUTDOWN operation.

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