SC561 datasheet(10/15 Pages) SEMTECH

10 / 15 page

SC561

General Description

The SC561 is a dual output linear regulator device

intended for applications where low dropout voltage, low

supply current, and low output noise are critical. The

device provides a simple, low cost solution for two

separate regulated outputs. Minimal 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 up to 300mA

of output current. The SC561 provides output voltages in

the range 1.2V to 3.3V. Available voltage values are shown

in the Voltage Options table on page 2.

Power On Control

The SC561 device has 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.

The outputs of both LDOA and LDOB are enabled when

EN transitions high. 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.

OUTA

PGOOD

OUTB

tSU

87%

200ms

87%

Figure 1 — Timing Diagram

As PGOOD is an open-drain output, it can be left uncon-

nected when it is not in use without affecting the

performance of the device.

Dynamic Bias Control

The LOAD pin provides dynamic bias control which allows

the device to be operated in a low quiescent current

mode at light loads. At loads less than 2mA, the LOAD

pin should be pulled low in order to force the device into

an ultra-low quiescent current mode. When the load is

increased above 2mA, the LOAD pin should be pulled

high to ensure normal operation. This pin is a logic input,

therefore it must never be left unconnected. Figure 2

shows the quiescent current versus load current with

both LDOs enabled.

Io (mA)

1.4

1.2

0.8

0.6

0.4

0.2

0.1

0.01

100

1000

LOAD = H

Figure 2a - Quiescent Current versus Output Current

Io (mA)

0.1

0.01

100

1000

0.02

LOAD = L

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

Figure 2b - Quiescent Current versus Output Current

Applications Information

SC561 Datasheet(PDF) 10 Page - Semtech Corporation

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