LT3029 LINER [Linear Technology], LT3029 Datasheet - Page 14

• Manufacturer Part Number: LT3029
• Description: Dual 500mA/500mA Low Dropout, Low Noise, Micropower Linear Regulator
• Manufacturer: LINER [Linear Technology]

LT3029
APPLICATIONS INFORMATION
2μF for the applied DC bias voltage and over the operat-
ing temperature range. 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.
Exercise care even 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 (voltage coeffi cient)
with X5R and X7R capacitors is better than with Y5V and
Z5U capacitors, but can still be signifi cant enough to drop
capacitor values below appropriate levels. Capacitor DC
bias characteristics tend to improve as case size increases.
Linear Technology recommends verifying expected versus
actual capacitance values at operating voltage in situ for
an application.
14
Figure 4. Noise Resulting from Tapping on a Ceramic Capacitor
500μV/DIV
V
OUT
C
C
I
LOAD
OUT
BYP
= 0.01μF
= 10μF
= 500mA
100ms/DIV
Voltage and temperature coeffi cients 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,
similar to the way a piezoelectric accelerometer or micro-
phone works. For a ceramic capacitor, the stress can be
induced by vibrations in the system or thermal transients.
The resulting voltages produced can cause appreciable
amounts of noise, especially when a ceramic capacitor is
used for noise bypassing. A ceramic capacitor produced
Figure 4’s trace in response to light tapping from a pencil.
Similar vibration induced behavior can masquerade as
increased output voltage noise.
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