DocID023654 Rev 2

17/27

ST1S41

Application information

So, if the inductor value decreases, the peak current (that must be lower than the current

limit of the device) increases. The higher the inductor value, the higher the average output

current that can be delivered, without reaching the current limit.

In Table 7 some inductor part numbers are listed.

6.3

Output capacitor selection

The current in the output capacitor has a triangular waveform which generates a voltage

ripple across it. This ripple is due to the capacitive component (charge or discharge of the

output capacitor) and the resistive component (due to the voltage drop across its ESR). So

the output capacitor must be selected in order to have a voltage ripple compliant with the

application requirements.

The amount of the voltage ripple can be calculated starting from the current ripple obtained

by the inductor selection.

Equation 22

For the ceramic capacitor (MLCC) the capacitive component of the ripple dominates the

resistive one. While for the electrolythic capacitor the opposite is true.

Since the compensation network is internal, the output capacitor should be selected in order

to have a proper phase margin and then a stable control loop.

The equations of Section 5.2 help to check loop stability given the application conditions,

the value of the inductor, and of the output capacitor.

In Table 8 some capacitor series are listed.

Table 7. Inductors

Manufacturer

Series

Inductor value (

μH)

Saturation current (A)

Coilcraft

XAL5030/6030

2.2 to 4.7

6.7 to 15.5

MSS1048

2.2 to 6.8

4.14 to 6.62

MSS1260

10

5.5

Wurth

WE-HC/HCA

3.3 to 4.7

7 to 11

WE-TPC typ XLH

3.6 to 6.2

4.5 to 6.4

WE-PD type L

10

5.6

TDK

RLF7030T

2.2 to 4.7

4 to 6

Table 8. Output capacitors

Manufacturer

Series

Cap value (

μF)

Rated voltage (V)

ESR (m

Ω)

MURATA

GRM32

22 to 100

6.3 to 25

< 5

GRM31

10 to 47

6.3 to 25

< 5

ΔV

OUT

ESR

ΔI

MAX

⋅

ΔI

MAX

8C

OUT

f

SW

⋅⋅

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