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LT3085

3085fa

APPLICATIONS INFORMATION

DC BIAS VOLTAGE (V)

3085 F02

–20

–40

–60

–80

–100

X5R

Y5V

BOTH CAPACITORS ARE 16V,

1210 CASE SIZE, 10μF

Figure 2. Ceramic Capacitor DC Bias Characteristics

TEMPERATURE (°C)

–50

–20

–40

–60

–80

–100

3085 F03

–25

100

125

Y5V

X5R

BOTH CAPACITORS ARE 16V,

1210 CASE SIZE, 10μF

Figure 3. Ceramic Capacitor Temperature Characteristics

For improvement in transient performance, place a capaci-

tor across the voltage setting resistor. Capacitors up to

1μF can be used. This bypass capacitor reduces system

noise as well, but start-up time is proportional to the time

constant of the voltage setting resistor (RSET in Figure 1)

and SET pin bypass capacitor.

Extra consideration must be given to the use of ceramic

capacitors. Ceramic capacitors are manufactured with a

variety of dielectrics, each with different behavior across

temperature and applied 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 capacitances

in a small package, but they tend to have strong voltage

and temperature coefﬁcients as shown in Figures 2

and 3. When used with a 5V regulator, a 16V 10μF Y5V

capacitor can exhibit an effective value as low as 1μF to

2μF for the DC bias voltage applied and over the operating

temperature range. The X5R and X7R dielectrics result in

more stable characteristics and are more suitable for use

as the output capacitor. The X7R type has better stability

across temperature, while the X5R is less expensive and is

available in higher values. Care still must be exercised when

using X5R and X7R capacitors; the X5R and X7R codes

only specify operating temperature range and maximum

capacitance change over temperature. Capacitance change

due to DC bias with X5R and X7R capacitors is better than

Y5V and Z5U capacitors, but can still be signiﬁcant enough

to drop capacitor values below appropriate levels. Capacitor

DC bias characteristics tend to improve as component

case size increases, but expected capacitance at operating

voltage should be veriﬁed.

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