STCF04 Datasheet, PDF (15/43 Pages) STMicroelectronics – Cell phones and smartphones

STCF04
7
Introduction
Introduction
The STCF04 is a high efficiency buck-boost converter with input current limitation dedicated
to managing the power for Flash/Torch mode operations using the SuperCap technology
and to control the high current white LEDs in cell phone cameras and portable applications
in general.
The device operates in Free-running mode with a coil peak current limiter. It charges and
stores the energy on the SuperCap from a single cell lithium-Ion battery (2.5 V to 4.2 V). The
device contains an active balancer circuit able to regulate the middle pin of the SuperCap,
therefore guaranteeing the reliability of the SuperCap component. The device operation and
diagnostic are controlled by the I²C bus. Torch current is adjustable from 15 mA to 320 mA.
The maximum flash current is set by choosing the R_FL resistor and it can be adjusted by I²C
using a dedicated register. The device operates as a standalone flash SuperCap controller
able to drive one external MOSFET.
The device has two modes of managing the energy in the SuperCap during Torch mode
operation, both adjustable by I²C:
1. Torch mode 1: in this case the output current in Torch mode is regulated from V_OUT,
which is set by V_DC bits in the feature register (R4). This mode is optimized to give the
possibility of triggering the flash without any delay caused by a recharging of the
SuperCap.
2. Torch mode 2: in this case the output current in Torch mode is regulated from V_OUT =
V_FLED + 0.25 V. This mode is optimized for maximum efficiency in Torch mode. The
SuperCap must be recharged after the end of Torch mode operation.
The device uses an external NTC resistor to sense the temperature of the white LEDs and
light sensor management to optimize the flash duration in Flash mode. These last two
functions are optional so they may not be needed in all applications, and, in such cases, the
relevant external components can be omitted. In Monitoring mode, when the voltage
Monitoring mode of the SuperCap is active, the device is working with low consumption.
When the READY pin goes HIGH, meaning that the SuperCap has been self-discharged,
the P should initiate a re-charge of the SuperCap, for example, by entering Charge mode.
Doc ID 022927 Rev 3
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