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ADT7310

system specific power supply IC that is suitable for color CCD camera

Advantech Co., Ltd. 

ADT7310

Application Hints

LDO CONSIDERATIONS

EXTERNAL CAPACITORS

The ADT7310’s regulators requires external capacitors for

regulator stability. These are specifically designed for CCTV

camera applications requiring minimum board space and

smallest components. These capacitors must be correctly sel-

ected for good performance.

OUTPUT CAPACITOR

The LDO’s are designed specifically to work with small cera-

mic output capacitors. And each LDO’s has its own output

capacitor ranges. Be sure to be connected proper output capa-

citor between the output pin and ground.

For using MLCC, output capacitor value is good to use more

than that of the specified to ‘Typical Application Circuit’.

And its required ESR range are between 10mΩ to 1Ω.

The output capacitor must meet the requirement for the min-

imum value of capacitance and also have an ESR value that

is within the optimum range for stability.

The LDO’s will remain stable and in regulation with no ext-

ernal load.

re range of -55℃ to +125℃, will only vary the capacitance to

within ±15%. The capacitor type X5R has a similar tolerance

over a reduced temperature range of -55℃ to +85℃. Many

large value ceramic capacitors, larger than 1uF are manufactu-

red with Z5U or Y5V temperature characteristics. Their capa-

citance can drop by more than 50% as the temperature varies

from 25℃ to +85℃. Therefore X7R is recommended over

Z5U and Y5V in applications where the ambient temperature

will change significantly above or below 25℃.

Tantalum capacitors are less desirable than ceramic for use as

output capacitors because they are more expensive when com-

paring equivalent capacitance and voltage ratings in the 0.47uF

to 4.7uF range.

Another important consideration is that tantalum capacitors ha-

ve higher ESR values than equivalent size ceramics. This mea-

ns that while it may be possible to find a tantalum capacitor

with an ESR value within the stable range, it would have to be

larger in capacitance than a ceramic capacitor with the same

ESR value. It should also be noted that the ESR of a typical

tantalum will increase about 2:1 as the temperature goes from

25℃ down to -40℃, so some guard band must be allowed.

CAPACITOR CHARACTERISTICS

The LDO’s are designed to work with ceramic capacitors on

the output to take advantage of the benefits they offer. For

capacitance values in the range of 0.47uF to 4.7uF, ceramic

capacitors are the smallest, least expensive and have the low-

est ESR values, thus making them best for eliminating high

frequency noise. The ESR of a typical 1.0uF ceramic capacitor

is in the range of 20mΩ to 40mΩ.

The capacitor value can change greatly, depending on the oper-

ation conditions and capacitor type. So, the output capacitor

selection should take account of all the capacitor parameters,

to ensure that the specification is met within the application.

The capacitance can vary with DC bias conditions as well as

temperature and frequency of operation. Normally increasing

the DC bias condition can result in the capacitance value fall-

ing below the minimum specified limit. It is therefore recom-

mended that the capacitor manufacturer’s specifications for

the nominal value capacitor are consulted for all conditions.

The ceramic capacitor’s capacitance can vary with temperatu-

re. The capacitor type X7R, which operates over a temperatu-

BUCK CONSIDERATIONS

INDUCTOR SELECTION

There are two main considerations when choosing an inductor;

the inductor should not saturate, and the inductor current ripple

is small enough to achieve the desired output voltage ripple.

Different saturation current rating specs are followed by differ-

ent manufacturers so attention must be given to details. Satura-

tion current ratings are typically specified at 25℃ so rating at

max ambient temperature of application should be requested

from manufacturer.

The saturation current is greater than the sum of the maximum

load current and the worst case average to peak inductor curr-

ent. A 47uH inductor with a saturation current rating of at least

590mA is recommended in this application. The inductor’s res-

istance should be as low as possible for better efficiency. For

CCTV camera application, radiated RF noise from inductor is

critical for high definitive video image. In this application,

a toroidal or shielded bobbin inductor should be used.

* This specifications are subject to be changed without notice

Oct. 17. 2008 / Rev. 0.0

10/15

http://www.ad-tech.co.kr

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