Functional description

STC3117

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DocID025792 Rev 2

6.3

Alarm output

The ALM pin provides an alarm signal in case of low battery or fault 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 any of the following conditions are

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)

•

the BATFAIL bit is set (if the ALM_ENA bit is set)

Low-voltage or low-SOC alarms

When a low-voltage or low-SOC condition is triggered, the STC3117 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 STC3117 is reset, the SOC and voltage alarms are enabled

(ALM_ENA bit = 1). The ALM pin is in high-impedance directly after a POR and is driven low

if the SOC and/or the voltage is below the default thresholds (1% SOC, 3.00 V), 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. Default value is 170 (i.e. 3.00 V).

BATFAIL alarm

The BATFAIL bit in REG_CTRL reflects the battery swap event: BATFAIL bit is set when the

BATD signal rises above the BATD threshold (1.61 V typ) for more than 0.5 s. and is reset

by writing 0 to the BATFAIL bit if the BATD signal is below the BATD threshold (if BATD is

still above 1.61 V, then BATFAIL bit can not be cleared).

The STC3117 drives the ALM pin low when the BATFAIL bit is set and releases the ALM pin

when the BATFAIL bit is cleared.