STC3105IQT Datasheet, PDF (12/23 Pages) STMicroelectronics – Battery monitor IC with alarm output for gas gauge applications

Functional description
STC3105
When the IO0DATA bit is 1 and the alarm function is enabled by the ALM_ENA bit, the ALM
pin is driven low if either of these two conditions is met:
● battery state-of-charge (SOC) less than the programmed threshold
● battery voltage less than the programmed low voltage level
When a low-voltage or low-SOC condition is triggered, the STC3105 drives the ALM pin low
and sets the ALM_VOLT or ALM_SOC bit in REG_CTRL.
The ALM pin remains low (even if the conditions disappear) until the software writes the
ALM_VOLT and ALM_SOC bits to 0 to clear the interrupt.
Clearing the ALM_VOLT or ALM_SOC while the corresponding low-voltage or low-SOC
condition is still true does not generate another interrupt; this condition must disappear first
and must be detected again before another interrupt (ALM pin driven low) is generated for
this alarm. The other alarm condition, if not yet triggered, can still generate an interrupt.
Usually, the low-SOC alarm occurs first to warn the application of a low battery condition,
then if no action is taken and the battery discharges further, the low-voltage alarm signals a
nearly-empty battery condition.
At power-up, or when the STC3105 is reset, the alarm output is disabled (ALM_ENA bit = 0),
the threshold levels (low-voltage alarm, low-SOC alarm) are cleared, and the base SOC and
relaxation counter are cleared.
6.6
Battery voltage relaxation timer
A battery relaxation timer is counted from the time that the current is below 0 and above the
current threshold, meaning the battery is in a light-load condition. The relaxation counter
register is an 8-bit read-only register clocked every 2 voltage conversion (8 s) and can go up
to about 30 min; when the counter reaches its max value 0xff, it stops at this max value. The
counter is cleared when the current is above 0 (charging) or below the current threshold
(high rate discharge).
The relaxation counter register is read from I²C by the gas gauge firmware to check that the
battery voltage had enough time to relax from the last time the current was high or charging.
The current threshold register is an 8-bit R/W register set by the gas gauge firmware from
I²C. It can be programmed from 0.1 to 100% of the full scale current range with 0.4% steps
Figure 5. Battery voltage relaxation counter
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12/23
Doc ID 022198 Rev 1