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.
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-
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.
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.
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.
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℃.
BUCK CONSIDERATIONS
* 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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