STC3117 datasheet(11/34 Pages) STMICROELECTRONICS

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STC3117

Functional description

6.1

Battery monitoring functions

6.1.1

Operating modes

The monitoring functions include the measurement of battery voltage, current, and

temperature. A Coulomb counter is available to track the SOC when the battery is charging

or discharging at a high rate. A sigma-delta A/D converter is used to measure the voltage,

current, and temperature.

The STC3117 can operate in two different modes with different power consumption (see

Table 7. Mode selection is made by the VMODE bit in register 0 (refer to Table 12 for

In mixed mode, current is measured continuously (except for a conversion cycle every 4 s

and every 16 s for measuring voltage and temperature respectively). This provides the

highest accuracy from the gas gauge.

In voltage mode with no current sensing, a voltage conversion is made every 4 s and a

temperature conversion every 16 s. This mode provides the lowest power consumption.

It is possible to switch between the two operating modes to get the best accuracy during

active periods, and to save power during standby periods while still keeping track of the

SOC information.

6.1.2

Battery voltage monitoring

Battery voltage is measured by using one conversion cycle of the A/D converter every 4 s.

The conversion cycle takes 213 = 8192 clock cycles. Using the 32768 Hz internal clock, the

conversion cycle time is 250 ms.

The voltage range is 0 to 4.5 V and resolution is 2.20 mV. Accuracy of the voltage

measurement is ±0.5 % over the temperature range. This allows accurate SOC information

from the battery open-circuit voltage.

The result is stored in the REG_VOLTAGE register (see Table 11).

Table 7. STC3117 operating modes

VMODE

Description

Mixed mode, Coulomb counter is active, voltage gas gauge runs in parallel

Voltage gas gauge with power saving

Coulomb counter is not used. No current sensing.

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