W-5200 5

8

Application Information

Ceramic Capacitors

Ceramic capacitors of different dielectric materials lose

their capacitance with higher temperature and voltage at

different rates. For example, a capacitor made of X5R or

X7R material will retain most of its capacitance from – 40 C

to 85 C whereas a Z5U or Y5V style capacitor will lose

considerable capacitance over that range.

Z5U and Y5V capacitors may also have voltage

coefficient causing them to lose 60% or more of their

capacitance when the rated voltage is applied. When

comparing different capacitors it is often useful consider the

amount of achievable capacitance for a given case size rather

than discussing the specified capacitance value. For

example, over rated voltage and temperature conditions, a

1 F, 10 V, Y5V ceramic capacitor in an 0603 case may not

provide any more capacitance than a 0.22 F, 10 V, X7R

available in the same 0603 case. For many W-5200/

5 applications these capacitors can be considered

roughly equivalent.

The capacitor manufacturer s data sheet should be

consulted to determine what value of capacitor is needed to

ensure the desired capacitance at all temperatures and

voltages.

Below

is

a

list

of

ceramic

capacitor

manufacturers and how to contact them:

Table 5. CERAMIC CAPACITOR MANUFACTURERS

Capacitor

Manufacturer

Web

Phone

Murata

www.murata.com

814.237.1431

AVX/Kemet

www.avxcorp.com

843.448.9411

Vishay

www.vishay.com

Kemet

www.kemet.com

408.986.0424

Taiyo Yuden

www.t yuden.com

408.573.4150

Thermal Management

For higher input voltages and maximum output current

there can be substantial power dissipation in the

. If the junction temperature increases to 160 C,

the thermal shutdown circuitry will automatically turn off

the output.

A good thermal connection to the PC board is

recommended to reduce the chip temperature. Connecting

the GND pin (Pin 2

to a ground plane, and maintaining a

solid ground plane under the device reduces the overall

thermal resistance.

o

which is defined by the package style, and the second path

dependent on board layout. The final operating junction

temperature for any set of conditions can be estimated by the

following thermal equation:

CA

The SOT23 package, when mounted on printed circuit

board with two square inches of copper allocated for “heat

spreading”, will result with an overall

150 C/W.

For a typical application operating from a 3.8 V input

supply, the maximum power dissipation is 260 mW

(100 mA x 3

This would result if a maximum junction

temperature of:

The use of multi layer board construction with power

planes will further enhance the overall thermal performance.

In the event of no dedicated copper area being used for heat

spreading, a multi l ayer board will typically provide the

conduction would allow up to 200 mW be safely

dissipated within the device.