LTC3025-3 LINER [Linear Technology], LTC3025-3 Datasheet - Page 13

• Manufacturer Part Number: LTC3025-3
• Description: 1A, 0.9V to 10V, Very Low Dropout Linear Regulator
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
and are more suitable for use as the output capacitor at
fractionally increased cost. X5R and X7R dielectrics both
exhibit excellent voltage coefficient characteristics. X7R
works over a larger temperature range and exhibits better
temperature stability whereas X5R is less expensive and
is available in higher values. Figures 2 and 3 show voltage
coefficient and temperature coefficient comparisons
between Y5V and X5R material.
Figure 3. Ceramic Capacitor Temperature Characteristics
Figure 2. Ceramic Capacitor DC Bias Characteristics
–100
–100
–20
–40
–60
–80
–20
–40
–60
–80
20
40
20
0
0
–50
0
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
2
–25
4
DC BIAS VOLTAGE (V)
0
TEMPERATURE (°C)
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
6
25
8
Y5V
X5R
50
10
Y5V
75
12
X5R
100
14
3022 F02
3022 F03
16
125
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,
similar to the way a piezoelectric accelerometer or
microphone 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. 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.
No-Load/Light-Load Recovery
A possible transient load step that occurs is where the
output current changes from its maximum level to zero
current or a very small load current. The output voltage
responds by overshooting until the regulator lowers the
amount of current it delivers to the new level. The regulator
loop response time and the amount of output capacitance
control the amount of overshoot. Once the regulator has
decreased its output current, the current provided by
the resistor divider (which sets V
remaining to discharge the output capacitor from the level
to which it overshot. The amount of time it takes for the
output voltage to recover easily extends to milliseconds
with minimum divider current and many microfarads of
output capacitance.
Figure 4. Noise Resulting from Tapping on a Ceramic Capacitor
1mV/DIV
V
C
I
LOAD
OUT
OUT
LT3022-1.5/LT3022-1.8
= 1.3V
= 10µF
= 0
LT3022/LT3022-1.2
1ms/DIV
OUT
) is the only current
3022 F04
13
3022fb