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LT3045-1

30451fa

For more information www.linear.com/LT3045-1

APPLICATIONS INFORMATION

Give extra consideration to the type of ceramic capacitors

used. They are manufactured with a variety of dielectrics,

eachwithdifferentbehavioracrosstemperatureandapplied

voltage. The most common dielectrics used are specified

with EIA temperature characteristic codes of Z5U, Y5V,

X5R and X7R. The Z5U and Y5V dielectrics are good for

providing high capacitance in the small packages, but they

tendtohavestrongervoltageandtemperaturecoefficients

as shown in Figure 4 and Figure 5. When used with a 5V

regulator,a16V10µFY5Vcapacitorcanexhibitaneffective

value as low as 1µF to 2µF for the DC bias voltage applied

over the operating temperature range.

X5R and X7R dielectrics result in more stable character-

istics and are thus more suitable for LT3045-1. The X7R

dielectric has better stability across temperature, while the

X5R is less expensive and is available in higher values.

Nonetheless, care must still be exercised when using

X5R and X7R capacitors. The X5R and X7R codes only

specify operating temperature range and the maximum

capacitance change over temperature. While capacitance

change due to DC bias for X5R and X7R is better than

Y5V and Z5U dielectrics, it can still be significant enough

to drop capacitance below sufficient levels. As shown in

Figure 6, capacitor DC bias characteristics tend to improve

as component case size increases, but verification of

expected capacitance at the operating voltage is highly

recommended.Duetoitsgoodvoltagecoefficientinsmall

case sizes, LTC recommends using Murata’s GJ8 series

ceramic capacitors.

High Vibration Environments

Voltage and temperature coefficients are not the only

sources of problems. Some ceramic capacitors have a

piezoelectric response. A piezoelectric device generates

voltageacrossitsterminalsduetomechanicalstressupon

it, similar to how a piezoelectric microphone works. For a

ceramiccapacitor,thisstresscanbeinducedbymechanical

vibrations within the system or due to thermal transients.

LT3045-1 applications in high vibration environments

have three distinct piezoelectric noise generators: ceramic

output, input, and SET pin capacitors. However, due to

LT3045-1’s very low output impedance over a wide fre-

quency range, negligible output noise is generated using

Figure 4. Ceramic Capacitor DC Bias Characteristics

Figure 5. Ceramic Capacitor Temperature Characteristics

Figure 6. Capacitor Voltage Coefficient for Different Case Sizes

DC BIAS VOLTAGE (V)

BOTH CAPACITORS ARE 16V,

1210 CASE SIZE, 10µF

–100

–80

30451 F04

–60

–40

X5R

Y5V

–20

TEMPERATURE (°C)

–50

–100

–80

–25

100

30451 F05

–60

–40

Y5V

–20

125

BOTH CAPACITORS ARE 16V,

1210 CASE SIZE, 10µF

X5R

DC BIAS (V)

–100

–80

–60

–40

–20

30451 F06

GRM SERIES, 0805, 1.45mm THICK

GRM SERIES, 1206, 1.8mm THICK

GRM SERIES, 1210, 2.2mm THICK

GJ8 SERIES, 1206, 1.9mm THICK

MURATA: 25V,10%,

X7R/X5R, 10µF CERAMIC

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