Datasheet

LT1965 Series
13
1965fb
For more information www.linear.com/LT1965
applications inForMation
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 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. A ceramic capacitor produced the trace
in Figure 5 in response to light tapping from a pencil.
Similar vibration induced behavior can masquerade as
increased output voltage noise.
Overload Recovery
Like many IC power regulators, the LT1965 has safe oper
-
ating area protection. The safe area protection decreases
current limit as input-to-output voltage increases and keeps
the power transistor inside a safe operating region for all
values of input-to-output voltage. The protective design
provides some output current at all values of input-to-
output voltage up to the device breakdown.
When power is first applied, as input voltage rises, the
output follows the input, allowing the regulator to start up
into very heavy loads. During start-up, as the input voltage
Figure 3. Ceramic Capacitor DC Bias Characteristics Figure 4. Ceramic Capacitor Temperature Characteristics
Figure 5. Noise Resulting from Tapping on a Ceramic Capacitor
DC BIAS VOLTAGE (V)
CHANGE IN VALUE (%)
1965 F03
20
0
–20
–40
–60
–80
–100
0
4
8
10
2 6
12
14
X5R
Y5V
16
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
TEMPERATURE (°C)
–50
40
20
0
–20
–40
–60
–80
–100
25 75
1965 F04
–25 0
50 100 125
Y5V
CHANGE IN VALUE (%)
X5R
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
1ms/DIV
1mV/DIV
1965 F05
V
OUT
= 1.3V
C
OUT
= 10µF
I
LOAD
= 0