ltc3025edc-4 Linear Technology Corporation, ltc3025edc-4 Datasheet - Page 7

• Manufacturer Part Number: ltc3025edc-4
• Description: 500ma Micropower Vldo Linear Regulators
• Manufacturer: Linear Technology Corporation

BLOCK DIAGRAM
APPLICATIONS INFORMATION
Operation (Refer to Block Diagram)
The LTC3025-X is a micropower, VLDO (very low dropout)
linear regulator which operates from input voltages as low
as 0.9V. The device provides a highly accurate output that
is capable of supplying 500mA of output current with a
typical dropout voltage of only 85mV. A single ceramic
capacitor as small as 1μF is all that is required for output
bypassing. A low reference voltage allows the LTC3025-1
output to be programmed to much lower voltages than
available in common LDOs (range of 0.4V to 3. 6V). The
LTC3025-2/LTC3025-3/LTC3025-4 have fi xed outputs of
1.2V, 1.5V and 1.8V respectively, eliminating the need for
an external resistor divider.
As shown in the Block Diagram, the BIAS input supplies
the internal reference and LDO circuitry while all output
current comes directly from the IN input for high effi ciency
regulation. The low quiescent supply currents I
I
shutdown making the LTC3025-X an ideal choice for use
in battery-powered systems.
The device includes current limit and thermal overload
protection. The fast transient response of the follower
output stage overcomes the traditional tradeoff between
dropout voltage, quiescent current and load transient
response inherent in most LDO regulator architectures.
The LTC3025-X also includes overshoot detection circuitry
which brings the output back into regulation when going
from heavy to light output loads (see Figure 1).
BIAS
= 50μA drop to I
1
6
2
BIAS
SHDN
GND
SHDN
REFERENCE
IN
0.4V
= 1μA, I
SOFT-START
LTC3025-1
BIAS
–
+
= 0.01μA typical in
6μA
IN
= 4μA,
OUT
ADJ
IN
3
4
5
Adjustable Output Voltage (LTC3025-1)
The output voltage is set by the ratio of two external resis-
tors as shown in Figure 2. The device servos the output
to maintain the ADJ pin voltage at 0.4V (referenced to
ground). Thus, the current in R1 is equal to 0.4V/R1. For
good transient response, stability, and accuracy, the current
1
6
2
BIAS
SHDN
GND
I
OUT
20mV/DIV
300mA
V
0mA
OUT
AC
SHDN
REFERENCE
LTC3025-1/LTC3025-2/
V
V
V
C
Figure 1. LTC3025-X Transient Response
IN
OUT
BIAS
OUT
Figure 2. Programming the LTC3025-1
LTC3025-3/LTC3025-4
0.4V
= 1.5V
LTC3025-2, LTC3025-3, LTC3025-4
= 1.2V
= 1μF
= 3.6V
GND
OUT
ADJ
SOFT-START
R2
R1
100μs/DIV
R1
40k
+
–
30251234 F02
C
OUT
V
6μA
R2
80k (LTC3025-2)
110k (LTC3025-3)
140k (LTC3025-4)
OUT
= 0.4V 1 +
30251234 F01
( )
SENSE
OUT
30251234 BD
IN
R2
R1
3
4
5
30251234fc
7