ZXLD1356 datasheet(21/29 Pages) DIODES

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ZXLD1356

Document number: DS33470 Rev. 3 - 2

21 of 29

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December 2010

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Application Information (Continued)

VIN Capacitor Selection

A low ESR capacitor should be used for input decoupling, as the ESR of this capacitor appears in series with the supply source

impedance and lowers overall efficiency. This capacitor has to supply the relatively high peak current to the coil and smooth the

current ripple on the input supply.

To avoid transients into the IC, the size of the input capacitor will depend on the VIN voltage:

VIN = 6 to 40V

CIN = 2.2µF

VIN = 40 to 50V

CIN = 4.7µF

VIN = 50 to 60V

CIN = 10µF

When the input voltage is close to the output voltage the input current increases which puts more demand on the input capacitor.

The minimum value of 2.2µF may need to be increased to 4.7µF; higher values will improve performance at lower input voltages,

especially when the source impedance is high. The input capacitor should be placed as close as possible to the IC.

For maximum stability over temperature and voltage, capacitors with X7R, X5R, or better dielectric is recommended. Capacitors

with Y5V dielectric are not suitable for decoupling in this application and should NOT be used.

When higher voltages are with CIN = 10µF, an electrolytic capacitor can be used provided that a suitable 1mF ceramic capacitor

is also used and positioned as close to the VIN pin as possible.

A suitable capacitor would be NACEW100M1006.3x8TR13F (NIC Components).

The following web sites are useful when finding alternatives:

ZXLD1356 Datenblatt(PDF) 21 Page - Diodes Incorporated