Datasheet

LT3045
17
Rev. B
For more information www.analog.com
APPLICATIONS INFORMATION
Give extra consideration to the type of ceramic capacitors
used. They 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 capacitance in the small packages, but they
tend to have stronger voltage and temperature coefficients
as shown in Figure 4 and Figure 5. 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
over the operating temperature range.
X5R and X7R dielectrics result in more stable character
-
istics and are thus more suitable for LT3045. 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. Due to its good voltage coefficient in small
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
voltage across its terminals due to mechanical stress upon
it, similar to how a piezoelectric microphone works. For a
ceramic capacitor, this stress can be induced by mechanical
vibrations within the system or due to thermal transients.
LT3045 applications in high vibration environments have
three distinct piezoelectric noise generators: ceramic
output, input, and SET pin capacitors. However, due to
LT3045’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
0
–100
CHANGE IN VALUE (%)
–80
642
8
10 12
3045 F04
14
0
20
–60
–40
X5R
Y5V
–20
16
TEMPERATURE (°C)
–50
–100
CHANGE IN VALUE (%)
–80
250–25
50
75 100
3045 F05
0
20
40
–60
–40
Y5V
–20
125
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
X5R
DC BIAS (V)
1
–100
CHANGE IN VALUE (%)
–80
–60
–40
–20
0
20
5 10 15 20
3045 F06
25
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
Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.