STCF04 Datasheet, PDF (30/43 Pages) STMicroelectronics – Cell phones and smartphones

Theory of operation
STCF04
10.2
10.2.1
Power-ON reset
This mode is initiated by applying a supply voltage above the V_{PW_ON RESET} threshold
value. An internal timing (~1 µs) defines the duration of this status. The logic blocks are
powered, but the device doesn't respond to any input. The registers are reset to their default
values, the ATN and SDA pins are in high-Z, and the I²C slave address is internally set by
reading the ADD pin configuration. After the internally defined time has elapsed, the
STCF04 automatically enters Shutdown mode. For the additional reset of the device, it is
also possible to use the RESET pin.
RESET pin function
The device is put into Reset mode when the logic level on the RESET pin is 0. The logic
blocks are powered, but the device doesn't respond to any input. The registers are reset to
their default values; the ATN and SDA pins are in high-Z. The RESET pin must stay in LOW
level for T_RESMIN time (1 µs) at least to guarantee correct resetting of the device. When the
reset function driven by the RESET pin is not needed, the RESET pin must be connected to
the V_BAT = V_IN.
Figure 14. Reset timing
10.3
Shutdown mode and NTC mode
In Shutdown mode only the I²C interface is live, accepting I²C commands and register
settings. The device enters this mode automatically after reset or by resetting the PWR_ON
bit from other operation modes. Power consumption is at the minimum (1 µA typ.), if NTC is
not activated (NTC_ON = 0). If the NTC_ON is set, the µP can measure the LED
temperature through an A/D converter connected to the NTC pin. When NTC circuits are
active and the V_REF-EXT is present, the typical current consumption is increased to 2 µA. It is
recommended to not leave the STCF04 in this status if battery drain must be minimized.
10.4
Monitoring mode
When the VDC voltage set by the FTR_REG is not 0, the comparator of the SuperCap
voltage is live. This comparator checks the voltage on the SuperCap continuously. If it is
higher than the V_SUPMAX threshold, then the READY pin is pulled low and stays low until the
voltage on the SuperCap is higher than V_SUPMAX - 200 mV.
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Doc ID 022927 Rev 3