0402, 6.3V, X5R

0603, 10V, X5R

0

1.0

2.0

3.0

4.0

5.0

DC BIAS (V)

20%

40%

60%

80%

100%

LP3985

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SNVS087AE – OCTOBER 2000 – REVISED MAY 2015

Figure 38. Graph Showing A Typical Variation In Capacitance vs DC Bias

The ceramic capacitor's capacitance can vary with temperature. The capacitor type X7R, which operates over a

temperature range of

−55°C to 125°C, will only vary the capacitance to within ±15%. The capacitor type X5R has

a similar tolerance over a reduced temperature range of

−55°C to 85°C. Most large value ceramic capacitors

(around 2.2 µF) are manufactured with Z5U or Y5V temperature characteristics. Their capacitance can drop by

more than 50% as the temperature goes from 25°C to 85°C. Therefore X7R is recommended over Z5U and Y5V

in applications where the ambient temperature will change 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. It should also be noted that the ESR of a typical tantalum will increase about

2:1 as the temperature goes from 25°C down to

−40°C, so some guard band must be allowed.

8.2.2.5 Noise Bypass Capacitor

Connecting a 0.01-µF capacitor between the CBYPASS pin and ground significantly reduces noise on the

regulator output. This cap is connected directly to a high impedance node in the band gap reference circuit. Any

significant loading on this node will cause a change on the regulated output voltage. For this reason, DC leakage

current through this pin must be kept as low as possible for best output voltage accuracy.

The types of capacitors best suited for the noise bypass capacitor are ceramic and film. High-quality ceramic

capacitors with either NPO or COG dielectric typically have very low leakage. Polypropolene and polycarbonate

film capacitors are available in small surface-mount packages and typically have extremely low leakage current.

Unlike many other LDOs, addition of a noise reduction capacitor does not effect the load transient response of

the device.

8.2.2.6 Thermal Considerations

CAUTION

Due to the limited power dissipation characteristics of the available SOT-23 (DBV) and

DSBGA (YZR) packages, all possible combinations of output current (IOUT), input

voltage (VIN), output voltage (VOUT), and ambient temperatures (TA) cannot be

ensured.

Power dissipation, PD is calculated from the following formula: PD = ((VIN – VOUT) × IOUT) .

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