LT1963 Linear, LT1963 Datasheet - Page 11

• Manufacturer Part Number: LT1963
• Description: 1.5A/ Low Noise/ Fast Transient Response LDO Regulators
• Manufacturer: Linear

APPLICATIO S I FOR ATIO
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.
Overload Recovery
Like many IC power regulators, the LT1963-X has safe
operating area protection. The safe area protection de-
creases the current limit as input-to-output voltage in-
creases and keeps the power transistor inside a safe
operating region for all values of input-to-output voltage.
The protection is designed to provide some output current
at all values of input-to-output voltage up to the device
breakdown.
Figure 4. Ceramic Capacitor Temperature Characteristics
Figure 3. 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, 10 F
2
–25
U
4
DC BIAS VOLTAGE (V)
0
TEMPERATURE ( C)
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10 F
6
25
U
8
Y5V
X5R
50
10
Y5V
75
12
W
X5R
14
100
1963 F03
1963 F04
16
125
U
When power is first turned on, as the input voltage rises,
the output follows the input, allowing the regulator to start
up into very heavy loads. During the 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 voltage to recover. Other regulators, such as the
LT1085, also exhibit this phenomenon, so it is not unique
to the LT1963-X.
The problem occurs with a heavy output load when the
input voltage is high and the output voltage is low. Com-
mon situations are immediately after the removal of a
short-circuit or when the shutdown pin is pulled high after
the input voltage has already been turned on. The load line
for such a load may intersect the output current curve at
two points. If this happens, there are two stable output
operating points for the regulator. With this double inter-
section, the input power supply may need to be cycled
down to zero and brought up again to make the output
recover.
Output Voltage Noise
The LT1963 regulators have been designed to provide low
output voltage noise over the 10Hz to 100kHz bandwidth
while operating at full load. Output voltage noise is typi-
cally 40nV/ Hz over this frequency bandwidth for the
LT1963 (adjustable version). For higher output voltages
(generated by using a resistor divider), the output voltage
noise will be gained up accordingly. This results in RMS
noise over the 10Hz to 100kHz bandwidth of 14 V
the LT1963 increasing to 38 V
Higher values of output voltage noise may be measured
when care is not exercised with regards to circuit layout
and testing. Crosstalk from nearby traces can induce
unwanted noise onto the output of the LT1963-X. Power
supply ripple rejection must also be considered; the LT1963
regulators do not have unlimited power supply rejection
and will pass a small portion of the input noise through to
the output.
RMS
LT1963 Series
for the LT1963-3.3.
11
RMS
1963fa
for