Application information

STOD1317B

14/22

DocID022607 Rev 2

7

Application information

7.1

External passive components

7.1.1

Inductor selection

The inductor is the key passive component for switching converters.

For the step-up converter an inductance between 3.3 µH and 6.8 µH is recommended.

It is very important to select the right inductor according to the maximum current the inductor

can handle in order to avoid saturation. The peak current for the step-up can be calculated

as:

Equation 1

where

fs: switching frequency. Use the minimum value of 1 MHz for worst case;

: efficiency of the step-up converter (0.80 at maximum load).

7.1.2

Input and output capacitor selection

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

order to filter any disturbance present in the input line and to obtain stable operation of the

step-up converter and LDO. A minimum real capacitance value of 3 µF must be guaranteed

7.2

Recommended PCB layout

The STOD1317B is a high frequency power switching device so it requires a proper PCB

layout in order to obtain the necessary stability and optimize line/load regulation and output

voltage ripple.

In order to minimize the ground noise, a common ground node for power ground (PGND)

and a different one for analog ground (GND) must be used. The exposed pad is connected

to PGND through vias.

Grounding is fundamental to the operation of DC-DC converters; run separate ground paths

for critical parts of the circuit (GND and Power GND), each connected back to a single

ground point.

Separate ground lines prevent the current and noise of one component from interfering with

other components. If using a ground plane, utilize “split” plane techniques to give effective

grounding. Use multiple vias to decrease the trace impedance to ground.

L

fs

V

2

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VIN

V

(

VIN

VIN

I

V

I

MID

MIN

MID

MIN

MIN

OUT

MID

BOOST

PEAK

















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