Not Recommended for New Designs

bq28550-R1

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SLUSAS4A – OCTOBER 2012 – REVISED SEPTEMBER 2014

7.3 Over-Temperature Indication

7.3.1 Over-Temperature: Charge

If during charging Temperature() reaches the threshold of OT Chg for a period of OT Chg Time and

AverageCurrent() > Chg Current Threshold, then the [OC] bit is set based on the charge fault configuration

setting of the CHG bit in the Control Status Register. When Temperature() falls to OT Chg Recovery, the [OC]

bit is reset.

If OT Chg Time = 0, the feature is completely disabled.

7.3.2 Over-Temperature: Discharge

If during discharging Temperature() reaches the threshold of OT Dsg for a period of OT Dsg Time, and

AverageCurrent()

≤ –Dsg Current Threshold, then the [DSGOFFREQ] bit is set. When Temperature() falls to

OT Dsg Recovery, the [DSGOFFREQ] bit is reset.

If OT Dsg Time = 0, the feature is completely disabled.

7.4 Gas Gauging

Gas gauging information is accessed through a series of commands called Standard Commands. Further

capabilities are provided by the additional Extended Commands set. Both sets of commands, indicated by the

general format Command(), are used to read and write information contained within the bq28550-R1 device

control and status registers, as well as their data flash locations. Commands are sent from the system to the

gauge using the bq28550-R1 device’s serial interface and can be executed during application development, pack

manufacture, or end-equipment operation.

Cell information is stored in the bq28550-R1 non-volatile data flash memory. Many of these data flash locations

are accessible during application development. They cannot, generally, be accessed directly during end-

equipment operation. Access to these locations is achieved by using the bq28550-R1 device’s companion

evaluation software, through individual commands, or through a sequence of data-flash-access commands. To

access a desired data flash location, the correct data flash subclass and offset must be known. The bq28550-R1

device provides 96 bytes of user-programmable data flash memory, partitioned into three, 32-byte blocks:

Manufacturer Info Block A, Manufacturer Info Block B, and Manufacturer Info Block C. For specifics on

accessing the data flash, see Manufacturer Information Blocks.

The bq28550-R1 device’s gas gauging prediction uses a Compensated End of Discharge Voltage (CEDV)

method. This algorithm mathematically models the cell voltage as a function of the battery state-of-charge (SOC),

temperature, and current. The algorithm also models the battery impedance (Z) as a function of SOC and

temperature, with other parameters included in the calculation. The battery voltage model is used to calibrate full

charge capacity (FCC), and the compensated battery voltage can be used to indicate low battery voltage or

alarm function through firmware settings (Low Battery %, Fully Discharged).

The bq28550-R1 device measures discharge activity by monitoring the voltage across a small-value series sense

resistor (5 m

Ω to 20 mΩ typ) located between the CELL– and the battery’s PACKN terminal. This information is

used to integrate the battery discharge capacity and to estimate state of charge Q. This is then calculated as a

percentage of maximum capacity Qmax to indicate remaining state-of-charge (RSOC). The maximum capacity

parameter is updated on every full discharge cycle. There are other factors to be considered in estimating RSOC,

such as battery impedance, temperature, and aging due to number of charge/discharge cycles. The equations

used to determine the battery capacity factor these variables into the calculation based on battery chemistry.

7.5 Protection

7.5.1 Overcharge Detector

device detects the overcharge state of the battery, and the COUT pin transitions to a low level. This prohibits

charging the battery by turning off the external charge control N-channel MOSFET.

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