Datasheet
LTC3025
6
3025fd
BLOCK DIAGRAM
3
1
6
2
4
5
IN
OUT
6µA
3025 BD
ADJ
GND
SHDN
BIAS
REFERENCE
SHDN 0.4V
SOFT-START
–
+
Operation (Refer to Block Diagram)
The LTC3025 is a micropower, VLDO (very low dropout)
linear regulator which operates from input voltages as
low as 0.9V. The device provides a high accuracy output
that is capable of supplying 300mA of output current with
a typical dropout voltage of only 45mV. A single ceramic
capacitor as small as 1µF is all that is required for output
bypassing. A low reference voltage allows the LTC3025
output to be programmed to much lower voltages than
available in common LDOs (range of 0.4V to 3. 6V).
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
IN
= 4µA,
I
BIAS
= 50µA drop to I
IN
= 1µA, I
BIAS
= 0.01µA typical in
shutdown making the LTC3025 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 also includes overshoot detection circuitry
which brings the output back into regulation when going
from heavy to light output loads (see Figure 1).
APPLICATIONS INFORMATION
300mA
0mA
I
OUT
V
OUT
AC
20mV/DIV
V
IN
= 1.5V
V
OUT
= 1.2V
V
BIAS
= 3.6V
C
OUT
= 1µF
100µs/DIV
3025 F01
Figure 1. LTC3025 Transient Response
Adjustable Output Voltage
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
in R1 should be at least 8µA, thus the value of R1 should
be no greater than 50k. The current in R2 is the current in
R1 plus the ADJ pin bias current. Since the ADJ pin bias
current is typically <10nA, it can be ignored in the output
voltage calculation. The output voltage can be calculated