STC3115 Datasheet, PDF (16/31 Pages) STMicroelectronics – Gas gauge IC with alarm output for handheld applications

Functional description
STC3115
6.3
Low battery alarm
The ALM pin provides an alarm signal in case of a low battery condition. The output is an
open drain and an external pull-up resistor is needed in the application. Writing the
IO0DATA bit to 0 forces the ALM output low; writing the IO0DATA bit to 1 lets the ALM
output reflect the battery condition. Reading the IO0DATA bit gives the state of the ALM pin.
When the IO0DATA bit is 1, the ALM pin is driven low if either of the following two conditions
is met:
• The battery SOC estimation from the mixed algorithm is less than the programmed
threshold (if the alarm function is enabled by the ALM_ENA bit).
• The battery voltage is less than the programmed low voltage level (if the ALM_ENA bit
is set).
When a low-voltage or low-SOC condition is triggered, the STC3115 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 in progress 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. Another 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 STC3115 is reset, the SOC and voltage alarms are enabled
(ALM_ENA bit = 1). The ALM pin is high-impedance directly after POR and is driven low if
the SOC and/or the voltage is below the default thresholds (1% SOC, 3.00 V voltage), after
the first OCV measurement and SOC estimation.
The REG_SOC_ALM register holds the relative SOC alarm level in 0.5 % units (0 to 100 %).
Default value is 2 (i.e. 1% SOC).
The REG_ALARM_VOLTAGE holds the low voltage threshold and can be programmed over
the full scale voltage range with 17.60 (2.20 * 8) mV steps. The default value is 170 (3.00 V).
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