STLD20D

Components selection

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7.2

The capacitance values and its intrinsic resistance (ESR) must be selected in order to

reduce the output ripple.

The ceramic capacitor technology offers the best compromise between the space and the

performance (low ESR, value, voltage rating). Nevertheless, their values changes with the

time as well as with temperature, DC bias voltage and switching frequency. Thus it might be

necessary to use higher capacitor value if low ripple is an absolute need.

7.3

1.3. D, Boost diode selection

The diode selection is based upon two major criteria:

●

Low losses to get the best converter efficiency

●

Mechanical size

7.3.1

Electrical characteristic

during the steady state. Note that, some transient voltages occurs during the commutation

period due to the leakage inductance of the PCB. Generally, a power diode with a maximum

reverse voltage equal or just higher than 20V suits perfectly. Therefore a Schottky diode

technology can be used.

Schottky diode has a low forward voltage, nevertheless they have an additional reverse

current which provides additional losses at high ambient temperature.

Table 5.

Reference selection

Name

Ref

Height (mm)

L typ (µH)

DCR (

Murata

LQH32CN4R7M33

2

4.7

0.15

0.65

LQH32CN100K33

2

10

0.3

0.45

LQH32CN4R7M53

1.55

4.7

0.15

0.65

LQH32CN100K53

1.55

10

0.3

0.45

Coilcraft

LP04815-472MXC

1.5

4.7

0.15

0.77

LP04815-103MXC

1.5

10

0.23

0.55

Wurth Elektronik

(WE)

744031100

1.65

10

0.205

0.74

744031150

1.65

15

0.285

0.62

744042100

1.8

10

0.15

1.3

Sumida

CDRH2014-100

1.855

10

0.294

0.7

CLS4D14

1.5

6.8

0.13

0.8

CLS4D14

1.5

10

0.18

0.65

TDK

VLF3010AT 100HR49

shielded

10

10

0.67

0.49