0

1.0

2.0

3.0

4.0

5.0

DC BIAS (V)

100%

80%

60%

40%

20%

0402, 6.3V, X5R

0603, 10V, X5R

LP5952

SNVS469F – OCTOBER 2006 – REVISED DECEMBER 2015

www.ti.com

Figure 10. Typical Variation In Capacitance vs DC Bias

Capacitance of the ceramic capacitor can vary with temperature. The capacitor type X7R, which operates over a

temperature range of –55°C to +125°C, only varies the capacitance to within ±15%. The capacitor type X5R has

a similar tolerance over a reduced temperature range of –55°C to +85°C. Many large value ceramic capacitors,

larger than 1 µF, are manufactured with Z5U or Y5V temperature characteristics. Their capacitance can drop by

more than 50% as the temperature varies from 25°C to 85°C. Therefore, X7R is recommended over Z5U and

Y5V in applications where the ambient temperature changes significantly above or below 25°C.

Tantalum capacitors are less desirable than ceramic for use as output capacitors because they are more

expensive when comparing equivalent capacitance and voltage ratings in the 1-µF to 4.7-µF range.

Another important consideration is that tantalum capacitors have higher ESR values than equivalent size

ceramics. This means 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 (which means bigger and more costly) than a ceramic

capacitor with the same ESR value. The ESR of a typical tantalum increases about 2:1 as the temperature goes

from 25°C down to –40°C, so some guard band must be allowed.

8.2.1.2.5

Power Dissipation and Device Operation

The permissible power dissipation for any package is a measure of the capability of the device to pass heat from

the power source, the junctions of the device, to the ultimate heat sink, the ambient environment. Thus the power

dissipation is dependent on the ambient temperature and the thermal resistance across the various interfaces

between the die and ambient air.

As stated in the Recommended Operating Conditions, the allowable power dissipation for the device in a given

package can be calculated using Equation 1:

PD = (TJ(MAX) – TA) / RθJA

(1)

With an RRθJA = 181°C/W, the device in the 5-pin DSBGA package returns a value of 552 mW with a maximum

junction temperature of 125°C at TA of 25°C or 221 mW at TA of 85°C.

The actual power dissipation across the device can be estimated by Equation 2:

PD = (VIN – VOUT) × IOUT

(2)

14

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