ST camera flash LED buck / boost converter to reduce standby power consumption

STMicroelectronics (ST) introduced a new power IC STCF02, to drive the latest mobile imaging devices, such as mobile phones, digital cameras and PDA, such as the need for flash large current white LED design. The company claims that STCF02 provides the maximum allowable white LED power can be extended to 3W, while taking pictures of the maximum distance between the camera and the camera to 1.5m. This component also extends the battery life, in shutdown mode, the standby current will be reduced to 1 A, power consumption is similar to other components of the 1/6. STCF02 also integrates a variety of protection circuits, including a circuit capable of automatically detecting and returning LED over temperature information.

STCF02 is a highly efficient (85%) boost / buck converter that can control the current delivered to a single high-power flash white LED. Because the output of white LED is proportional to the current flowing through LED, it is very important to control the current accurately in the battery voltage range. The method of controlling the current of STCF02 is to adjust the forward voltage of white LED according to the battery voltage by the automatic switching mode between the buck and boost. The component uses pulse width modulation (PWM) control method, the switching frequency is 1.8MHz, through a lithium battery can provide 2.5V to 5.3V output voltage regulator. Three logic input signals allow the selection of four different modes of operation: flash, medium flash, flare and shutdown mode. Flash, flash and flare mode current can be set by external resistors. In shutdown mode, the LED is disconnected from the battery to cut off the leakage current from the battery.

In flash mode, the current range is from 200mA to 800mA, and the flare mode current can be adjusted between 25mA and 250mA. Meanwhile, the current in the flash mode can be set between the flare mode and the full flash mode. In order to ensure the reliability of work and the integration of the STCF02 electric circuit, if the inductor current exceeds the current limit value of PWM internal 2.3A, the controller will turn off the power switch inside, until the next PWM oscillation begins. The component contains the output overvoltage protection (OVP) function, when the output voltage is detected, it will stop the work of the PWM controller; when the output voltage is lower than the internal set value, it will automatically resume the normal operation mode. An internal thermal shutdown protection switch turns off the assembly when the junction temperature exceeds 140. In addition, the STCF02 can detect the temperature of white LED by the external negative temperature coefficient (NTC) sensor, once the white LED has been detected over temperature phenomenon, the component will automatically shut down. The external RC delay unit can be used to replace the NTC in order to limit the maximum flash time to a safe time.

Ordering quantity of 5000 to 10000 pieces, STCF02 unit price of $1, the sample has been put on the market, mass production is about to begin.