STCF07 datasheet(12/26 Pages) STMICROELECTRONICS

12 / 26 page

Detailed description

STCF07

12/26

Doc ID 16757 Rev 3

Detailed description

8.1

Buck-boost converter

The regulation of the PWM controller is done by sensing the current of the LED through RLC

or RLC + RHC, depending on the CSEL voltage. Depending of the forward voltage of the

flash LED, the device can automatically change between buck (step-down) and boost (step-

up) mode:

–

Boost region = VOUT > VBAT: this configuration is used in most cases, as the

output voltage (VOUT = VF + ILED x RSENSE) is higher than VBAT

–

Buck region = VOUT < VBAT

–

Buck / boost region = VOUT ~ VIN

8.2

High current mode

ENABLE = CSEL = VBAT

The STCF07 operates continuously to supply maximum current to the LED up to 800 mA in

high current mode. If high current mode is used in flash applications, then it is possible to

increase the LED current up to 1066 mA.

The current can be adjusted with the RHC resistor. The current is then programmed at:

IHC = 160 mV / RHC

For a current programmed at 800 mA, the sensing resistor is equal to 0.20

Ω.

8.3

Low current mode

ENABLE = VBAT, CSEL = 0

The STCF07 can continuously provide an adjustable current starting from 20 mA in low

current mode. The current adjustment is done with resistor RLC. The current is then

programmed at:

ILC = 160 mV / (RHC + RLC)

The NTC divider for measurement of the LED temperature is active.

8.4

Shutdown mode

ENABLE = 0

When the device is not used, it can be put in shutdown mode, which reduces the quiescent

current to 1 µA. The NTC protection in this mode is not active.

8.5

Soft-start

To avoid spikes on the battery during the startup sequence, a soft-start function has been

implemented. The soft-start function is achieved by progressively increasing the feedback

voltage reference. In worst-case conditions, the startup time, as defined below (IOUT = IMAX),

does not exceed 2 ms.

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