STCF07 Datasheet, PDF (12/26 Pages) STMicroelectronics – High power buck-boost white LED driver

Detailed description
8
Detailed description
STCF07
8.1
Buck-boost converter
The regulation of the PWM controller is done by sensing the current of the LED through R_LC
or R_LC + R_HC, 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 = V_OUT > V_BAT: this configuration is used in most cases, as the
output voltage (V_OUT = V_F + I_LED x R_SENSE) is higher than V_BAT
– Buck region = V_OUT < V_BAT
– Buck / boost region = V_OUT ~ V_IN
8.2
High current mode
ENABLE = CSEL = V_BAT
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 R_HC resistor. The current is then programmed at:
I_HC = 160 mV / R_HC
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 R_LC. The current is then
programmed at:
I_LC = 160 mV / (R_HC + R_LC)
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
12/26
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 (I_OUT = I_MAX),
does not exceed 2 ms.
Doc ID 16757 Rev 3