STCF04TBR datasheet(30/43 Pages) STMICROELECTRONICS

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Theory of operation

STCF04

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Doc ID 022927 Rev 3

10.2

Power-ON reset

This mode is initiated by applying a supply voltage above the VPW_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.

10.2.1

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 TRESMIN 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 VBAT = VIN.

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 VREF-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 VSUPMAX threshold, then the READY pin is pulled low and stays low until the

voltage on the SuperCap is higher than VSUPMAX - 200 mV.

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