AN2827

Selection of external components

Doc ID 15047 Rev 1

5/30

2

Selection of external components

2.1

Input and output capacitor selection

It is recommended to use ceramic capacitors with low ESR as input and output capacitors. It

is also recommended to use 10 µF/6.3 V as a minimum value for the input capacitor, and

1 µF/16 V as the optimal value for the output capacitor to achieve a good stability of the

device, for a supply range varying from a low input voltage (2.5 V) to the maximum ratings of

output power.

Note:

See recommended components in Table 1.

2.2

Inductor selection

A thin shielded inductor with a low DC series resistance of winding is recommended for this

application. To achieve a good efficiency in step-up mode, we recommend using an inductor

the LED [

Ω; Ω, 1].

For nominal operation, the peak inductor current can be calculated by the formula:

Where:

η

Efficiency of the STCF05

L

Inductance value of the inductor

F

Switching frequency

Note:

See recommended components in Table 1.

2.3

LED selection

Any string of LEDs with a cumulative forward voltage ranging from 5.3 to 10.2 V is

compatible with the STCF05. The total LED spread must be taken into account when

calculating the minimum and maximum voltage of the LEDs that must be inside the

5.3 –10.2 voltage range. It is possible to set the level of the LED current to flash mode and

torch mode by setting the corresponding registers through the I²C interface.

Note:

See recommended components in Table 1.

2.4

Optionally, the STCF05 uses a negative thermistor (NTC) to sense the LED temperature, as

Refer to Figure 3: Typical application schematic for more details.