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BQ78350-R1A

SLUSE05 – DECEMBER 2019

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9.2.3.1.4

Temperature

By default, the 78350 uses an external negative temperature coefficient (NTC) thermistor connected to the

BQ76920 as the source for the Temperature() data. The measurement uses a polynomial expression to

transform the BQ76920 ADC measurement into 0.1°C resolution temperature measurement. The default

polynomial coefficients are calculated using the Semitec 103AT, although other resistances and manufacturers

can be used.

To calculate the External Temp Model coefficients, use the BQ78350-R1 Family Thermistor Coefficient

Calculator shown in the application report, Using the BQ78350-R1 (SLUA924).

For improved accuracy, offset calibration is available for this value and can be managed through the BQSTUDIO

tool. The procedure for calibration is described in the BQ78350-R1A Technical Reference Manual (SLUUBD3) in

the Calibration chapter.

9.2.3.2 Gas Gauging

The default battery chemistry (Chem ID) is 1210, which is a Li-CoO2 type chemistry. The Chem ID should be

updated using BQSTUDIO to select the specific battery used in the application. See the application report, Using

the BQ78350-R1 (SLUA924) for details on selecting the Chem ID.

The default maximum capacity of the battery is 4400 mAh and this should be changed based on the cell and

battery configuration chosen.

The CEDV gas gauging algorithm requires seven coefficients to enable accurate gas gauging. The default values

are generic for Li-CoO2 chemistry, but for accurate gas gauging these coefficients should be re-calculated. The

procedure

to

gather

the

required

data

and

generate

the

coefficients

can

be

found

at

http://www.ti.com/tool/GPCCEDV.

More details on the required steps to set up the BQ78350-R1A device for gas gauging can be found in the

application report, Using the BQ78350-R1 (SLUA924).

9.2.3.3 Charging

The charging algorithm in the BQ78350-R1A device is configured to support Constant Voltage/Constant Current

(CC/CV) charging of a nominal 18-V, 4400-mAh battery.

9.2.3.3.1

Fast Charging Voltage

The charging voltage is configured (Fast Charging: Voltage) based on an individual cell basis (for example, 4200

mV), but the ChargingVoltage() is reported as the required battery voltage (for example, 4200 mV × 5 =

21000 mV).

9.2.3.3.2

Fast Charging Current

The fast charging current is configured to 2000 mA (Fast Charging: Current) by default, which is conservative for

the majority of 4400-mAh battery applications. This should be configured based on the battery configuration, cell

manufacturer's data sheet, and system power design requirements.

9.2.3.3.3

Other Charging Modes

The BQ78350-R1A device is configured to limit, through external components, and report either low or 0

ChargingVoltage() and ChargingCurrent(), based on temperature, voltage, and fault status information.

The Charge Algorithm section of the BQ78350-R1A Technical Reference Manual (SLUUBD3) details these

features and settings.

9.2.3.4 Protection

The safety features and settings of the BQ78350-R1A device are configured conservatively and are suitable for

bench evaluation. However, in many cases, users will need to change these values to meet system

requirements. These values should not be changed to exceed the safe operating limits provided by the cell

manufacturer and any industry standard.

For details on the safety features and settings, see the Protections and Permanent Fail sections of the

BQ78350-R1A Technical Reference Manual (SLUUBD3).