SC560

12

General Description

The SC560 is a family of dual output linear regulator devices

intended for applications where low dropout voltage, low

supply current, and low output noise are critical. Each

device provides a very simple, low cost solution for two

separate regulated outputs. Very little PCB area is required

due to the miniature package size and the need for only

four external capacitors.

The linear regulators LDOA and LDOB are powered from

a single input supply rail, and each provides 300mA of

output current. The SC560 can provide output voltages

in the range 1.2V to 5.0V. The output voltages for the

SC560A, SC560B and SC560C are set by connecting

external resistor dividers to the feedback pins of each

LDO. All other versions of the SC560 have xed output

voltage values shown in the Pinout and Voltage Options

detailed application circuits for each version.

Power On Control

The SC560A and SC560C devices have a single enable pin

(EN) that controls both LDO outputs. Pulling this pin low

causes the device to enter a low power shutdown mode

where it typically draws 100nA from the input supply.

When EN transitions high, the output of LDOA is enabled.

After a delay of 128μs, the output of LDOB is enabled. In

the SC560C, when the output voltage of LDOA reaches

87% of its regulation point, the delay timer starts and the

PGOOD signal transitions high after a delay of 200ms. The

power up/down sequence is shown in the timing diagram

in Figure 1.

OU T A

PG O OD

EN

OU T B

87 %

87 %

200 ms

128 µs

Figure 1 — Timing Diagram

The SC560B and the

xed output variants provide a

separate enable pin for LDOB which allows LDOA and

LDOB to be enabled independently. The EN pin controls

the LDOA output and the ENB provides the same

functionality relative to the LDOB output. The table

shown below lists the e ect of the polarity of the EN and

ENB signals on the outputs of LDOA and LDOB. Note from

the table that LDOB can only be enabled when LDOA is

already active. Since LDOB can be enabled separately,

there is no timing relationship between the two outputs

at startup.

EN

ENB

LDOA

LDOB

Low

Low

O

O

Low

High

O

O

High

Low

On

O

High

High

On

On

The SC560C and the xed output variants have a PGOOD

signal which monitors the output of LDOA and transitions

high 200ms after LDOA has reached 87% of its regulation

point. This can be used to hold a processor in reset when

the output voltage is out of regulation. Note that when

LDOA drops out of regulation and PGOOD is forced low,

LDOB is also disabled until PGOOD is reset.

Output Voltage Selection

The output voltage of each LDO for the SC560A, SC560B,

and SC560C version is set independently using external

resistor dividers. Figure 2 illustrates the proper connection

for LDOA.

OU T A

FB A

Figure 2 — Output Voltage Feedback Circuit

Applications Information