STCF07 Datasheet, PDF (20/26 Pages) STMicroelectronics – High power buck-boost white LED driver

External component selection
11 External component selection
STCF07
11.1
Note:
Input and output capacitor selection
For input and output capacitors it is recommended to use ceramic capacitors with low ESR.
For good device stability when supplied by a low input voltage of 2.7 V at maximum ratings,
it is recommended to use 10 µF / 6.3 V as a minimum value for the input capacitor, and 4.7
µF / 6.3 V as a minimum value for the output capacitor.
See recommended components in Table 5 on page 7.
11.2
Note:
Inductor selection
A thick, shielded inductor with low DC series wiring resistance is recommended for this
application. For good efficiency, it is recommended to use an inductor with a series DC
resistance of R_DCL < R_D / 10, where R_D is the dynamic resistance of the LED.
For nominal operation, the peak inductor current can be calculated using the formula:
I_PEAK = {(I_OUT / η) + [(V_OUT - V_IN) x V_IN²) / (2 x L x F x V_OUT²)]} x V_OUT / V_IN
where:
I_PEAK = peak inductor current
I_OUT = current sourced at pin V_OUT
η = efficiency of the STCF07
V_OUT = output voltage at pin V_OUT
V_IN = input voltage at pin V_IN
L = inductance value of the inductor
F = switching frequency
See recommended components in Table 5 on page 7.
11.3
Note:
LED selection
All LEDs with forward voltages from 2.7 V to 5 V are suitable for use with STCF07 device.
The LED forward voltage must include the voltage spread of this value. It is possible to set
the LED current in the two different operating modes (high current mode and low current
mode) through two external sensing resistors.
See recommended components in Table 5 on page 7.
11.4
R_HC selection
The R_HC resistor value can be calculated using equations R_HC = 160 mV / I_HC and P_RHC =
R_HC * I_HC2, where P_RHC is the dissipated power on the R_HC resistor. It is recommended to
use a 1206 package size thin metal film resistor with 1% or 5% maximum tolerance. The
maximum high LED current for the STCF07 device is 800 mA with a battery voltage range
2.7 V to 5.5 V.
20/26
Doc ID 16757 Rev 3