SC1458

9

General Description

The SC1458 is a dual output linear regulator intended

for applications where low dropout voltage, low supply

current, and low output noise are critical. The device

provides a very simple, low cost solution for two separate

regulated outputs using very little PCB area due to its

small package size and the need for only three external

capacitors.

Both linear regulators are powered from a single input

voltage supply rail, and each provides 300mA of output

current. Output voltages are set internally, eliminating the

need for external resistors.

An active high enable pin (EN) controls operation of both

regulators. Pulling this pin low causes the device to enter a

very low power shutdown mode, where it typically draws

100nA from the input supply.

The device is available in two versions: SC1458A and

SC1458B. The SC1458A version has pin 6 configured as a

power good signal (PGOOD), which monitors the output

of LDOA. The SC1458B device has pin 6 configured as an

external bypass pin (BYP). This is suitable for applications

which require low output noise and excellent PSRR

characteristics.

Power-On Control

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

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

In the case of the SC1458A, 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

Figure 1.

OUTA

PGOOD

EN

OUTB

87%

200 ms

128μs

87%

Figure 1 — Timing Diagram

Active Shutdown

The SC1458 has internal active shutdown circuitry

included for both LDOs. Shutdown behavior is controlled

by discharging the output capacitor on the LDO output

by an on-chip FET when the LDO is disabled.

Protection Circuitry

The device provides the following protection features to

ensure that no damage is incurred in the event of a fault

condition.

Under-Voltage Lockout

Over-Temperature Protection

Short-Circuit Protection

Under-Voltage Lockout

The Under-Voltage LockOut (UVLO) circuit protects the

device from operating in an unknown state if the input

voltage supply is too low.

When the V

IN

drops below the UVLO threshold, the

LDOs are disabled and discharged — PGOOD is held

low (SC1458A only). When V

IN

is increased above the

hysteresis level, the LDOs are enabled into their previous

states (timing described in Figure 1), provided EN has

remained high. When powering-up with V

IN

below the

UVLO threshold, the LDOs will remain off and PGOOD

will be held low (SC1458A only).

Over-Temperature Protection

An internal over-temperature (OT) protection circuit is

provided that monitors the internal junction temperature.

When the temperature exceeds the OT threshold as

defined in the Electrical Characteristics section, the OT

protection disables all the LDO outputs and holds the

PGOOD signal low. When the junction temperature drops

below the hysteresis level, the LDOs are re-enabled into

their previous states and PGOOD is set high, provided EN

has remained high (SC1458A only).

Short-Circuit Protection

Each LDO output has short-circuit protection. If the

output current exceeds the current limit, the output

voltage will drop and the output current will be limited

until the short is removed. If a short-circuit occurs on the

output of LDOA, the output of LDOB will also be disabled

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Applications Information