LT3050EDDB LINER [Linear Technology], LT3050EDDB Datasheet - Page 16

• Manufacturer Part Number: LT3050EDDB
• Description: 100mA, Low Noise Linear Regulator With Precision Current Limit And Diagnostic Functions
• Manufacturer: LINER [Linear Technology]

LT3050
APPLICATIONS INFORMATION
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 technical stress, similar
to the way a piezoelectric accelerometer or microphone
works. For a ceramic capacitor, the stress is induced by
vibrations in the system or thermal transients. The resulting
voltages produced 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.
16
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
–25
2
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
3050 F02
3050 F03
125
16
Overload Recovery
Like many IC power regulators, the LT3050 has safe
operating 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 LT3050 provides some output current at all values of
input-to-output voltage up to the device breakdown.
When power is fi rst applied, the input voltage rises and 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
the removal of an output short will not allow the output
to recover. Other regulators, such as the LT1083/LT1084/
LT1085 family and LT1764A also exhibit this phenomenon,
so it is not unique to the LT3050. The problem occurs with
a heavy output load when the input voltage is high and the
output voltage is low. Common situations are: immediately
after the removal of a short-circuit or if the shutdown pin
is pulled high after the input voltage is already turned on.
The load line for such a load intersects the output current
curve at two points. If this happens, there are two stable
output operating points for the regulator. With this double
intersection, the input power supply needs to be cycled
down to zero and brought up again to make the output
recover.
Figure 4. Noise Resulting from Tapping on a Ceramic Capacitor
1mV/DIV
V
OUT
10ms/DIV
V
C
C
OUT
OUT
REF/BYP
= 5V
= 10μF
= 10nF
3050 F04
3050f