ltc3025-2 Linear Technology Corporation, ltc3025-2 Datasheet - Page 11

• Manufacturer Part Number: ltc3025-2
• Description: 500ma Micropower Vldo Linear Regulators Features
• Manufacturer: Linear Technology Corporation

applicaTions inForMaTion
Soft-Start Operation
The LTC3025-X includes a soft-start feature to prevent
excessive current flow during start-up. When the LDO is
enabled, the soft-start circuitry gradually increases the LDO
reference voltage from 0V to 0.4V over a period of about
600µs. There is a short 700µs delay from the time the
part is enabled until the LDO output starts to rise. Figure 5
shows the start-up and shutdown output waveform.
200mV/DIV
SHDN
V
OUT
1.2V
OFF
ON
0V
Figure 5. Output Start-Up and Shutdown
T
V
V
C
R
A
IN
BIAS
OUT
LOAD
= 25°C
= 1.5V
= 1µF
= 3.6V
= 4Ω
500µs/DIV
30251234 F05
V
During power-up, the output shutdown circuitry is not
active below V
the output voltage can drift up during power-up due to
leakage current (<1 mA typical) from V
input, the shutdown circuitry is active and the output is
actively held off. This usually causes no circuit problems
and is similar to 3-terminal regulators such as the LT3080,
LT1086 and LT317 which have no ground pin and can have
the output rise under some conditions. A slowly rising
V
ramping of V
V
With fast rising inputs (>1V/ms) or with sufficient resis-
tive load on V
reduced or eliminated. Such conditions also reduce or
eliminate non-monotonic initial power-up with the part
enabled. If V
current from V
circuitry is active at a V
to minimize V
before V
in shutdown or it is actively held on when enabled under
all conditions.
OUT
IN
IN
of about 0.65V (typical) as well.
with the part enabled may result in non-monotonic
Start-Up and Supply Sequencing
BIAS
LTC3025-1/LTC3025-2/
LTC3025-3/LTC3025-4
. At V
BIAS
OUT
OUT
OUT
IN
IN
to V
of about 0.65V DC (typical). As a result,
due to LDO circuitry becoming active at
is sequenced up before V
, output voltage rise during power-up is
IN
rise during start-up, sequence up V
= 0.9V, the output is actively held off
OUT
IN
may increase until the shutdown
of about 0.65V typical. Thus,
IN
to V
IN
, the leakage
OUT
. At 0.9V

30251234fe
IN