Functional description

STC3100

10/21

clock, the conversion cycle time is 125 to 500 ms for a 12- to 14-bit resolution. The LSB

value is set by the internal gain and internal reference and is 11.77 uV at maximum

resolutions. When using an external 30 milliOhms sense resistor, the 28-bit accumulator

results in a capacity of approximately +/- 7300 mA.h. The upper 16 bits of the accumulator

can be read from the I2C interface, giving a resolution of 0.2 mA.h.

When the battery voltage falls below the under voltage lockout threshold at 2.7 V, the gas

gauge system is stopped and the STC3100 stays in standby mode with minimum quiescent

current. All registers are maintained down to 2.0 V. Below 2.0 V, the registers are reset to

their default power-on value.

The gas gauge system needs an accurate 32,768 Hz timebase to compute the level of

charge flowing from/to the battery. The STC3100 can operate from an internal oscillator, or

use an external RTC signal for highest accuracy.

7.2

Battery voltage and temperature monitoring

The battery voltage and chip temperature (close to the battery temperature) are measured

by means of an A/D converter and a multiplexer. This function takes place concurrently to

the gas gauge function with a dedicated A/D converter, which means that it does not affect

the performance of the gas gauge. To reduce the power consumption, a conversion takes

place only every two seconds, alternatively for battery voltage and temperature (so each

value is refreshed every four seconds).

conversion cycle time is 250 ms. The resolution is 2.44 mV for the battery voltage and

0.125° C for the temperature.

7.3

General-purpose input/output

A general-purpose I/O line is available. The output is an open drain, and an external pull-up

resistor may be needed in the application. Writing the IO0DATA bit to 0 forces the IO0 output

low; writing the IO0DATA bit to 1 leaves the IO0 output in a high impedance state. Reading

the IO0DATA bit gives the state of the IO0 pin.

In standby (CG_RUN=0), reset (PORDET set to 1) and power-down (Vcc<UVLOth) states,

the IO0 output is open and the input is read as zero whatever is the actual state of the IO0

pin.

7.4

RAM registers

The STC3100 provides 32 RAM registers to store any information regarding battery status,

charge cycles, battery aging, proprietary informations, etc...

The register content is maintained during standby and low voltage states, down to the

power-on reset level of approximately 2.0 V. Below this level, the content is not preserved.

This usually means that the Li-Ion cell was very deeply discharged and has been damaged.