LTC3025-1/LTC3025-2/

LTC3025-3/LTC3025-4

7

30251234fc

BLOCK DIAGRAM

3

1

6

2

4

5

IN

OUT

6μA

ADJ

GND

SHDN

BIAS

REFERENCE

SHDN

0.4V

SOFT-START

–

+

3

1

6

2

4

5

IN

OUT

6μA

30251234 BD

SENSE

GND

SHDN

BIAS

REFERENCE

SHDN

0.4V

SOFT-START

–

+

R1

40k

R2

80k (LTC3025-2)

110k (LTC3025-3)

140k (LTC3025-4)

LTC3025-1

LTC3025-2, LTC3025-3, LTC3025-4

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 fixed 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 efficiency

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).

Figure 1. LTC3025-X Transient Response

300mA

0mA

AC

20mV/DIV

100μs/DIV

30251234 F01

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

APPLICATIONS INFORMATION

Figure 2. Programming the LTC3025-1

()

OUT

R1

R2

30251234 F02

R2

R1

ADJ

GND