ZXLD1366 datasheet(21/32 Pages) DIODES

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ZXLD1366

Document number: DS31992 Rev. 5 - 2

21 of 32

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June 2010

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Diodes Incorporated

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 2.2

μF 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 used with the 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:

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