LT1764A LINER [Linear Technology], LT1764A Datasheet - Page 9

• Manufacturer Part Number: LT1764A
• Description: 1.1A, Low Noise, Low Dropout Linear Regulator
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
capacitor values below appropriate levels. Capacitor DC
bias characteristics tend to improve as component case
size increases, but expected capacitance at operating
voltages should be verifi ed.
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. A ceramic capacitor produced the trace
in Figure 4 in response to light tapping from a pencil.
Similar vibration induced behavior can masquerade as
increased output voltage noise.
Figure 2. Ceramic Capacitor DC Bias Characteristics
–100
–20
–40
–60
–80
20
0
0
2
4
DC BIAS VOLTAGE (V)
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10μF
6
8
Y5V
X5R
Figure 4. Noise Resulting from Tapping on a Ceramic Capacitor
10
12
1mV/DIV
14
1965 F02
16
V
C
I
LOAD
OUT
OUT
= 1.3V
= 10μF
= 0
1ms/DIV
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 fi rst 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
is rising, the input-to-output voltage differential is small,
allowing the regulator to supply large output currents. With
a high input voltage, a problem can occur wherein removal
of an output short will not allow the output to recover.
Figure 3. Ceramic Capacitor Temperature Characteristics
–100
1965 F04
–20
–40
–60
–80
40
20
0
–50
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10μF
–25
0
TEMPERATURE (°C)
25
50
Y5V
75
X5R
100
1965 F03
125
LT1965
9
1965f