SC573 datasheet(12/17 Pages) SEMTECH

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SC573

Final Rev2.1

Applications Information

General Description

SC573 is a linear regulator with low dropout voltage,

low supply current, and low output noise. The device

provides a simple, low cost solution with minimal PCB

area. It has a miniature package size and needs two 1µF

0402 size external capacitors for its input and output.

The LDO provides up to 300mA output current.

Power On and Off Control and Turn-on Delay

SC573 device has an enable pin (EN) that controls the

LDO output. Pulling the enable pin high will enable the

device when VIN is above its UVLO level at about 2.4V.

Pulling this pin low causes the device to shutdown

where it typically draws 100nA from the input supply.

When the enable pin is connected to the input voltage

supply, the device turn-on and turn-off has two voltage

thresholds to overcome. At the turn-on event, the enable

pin voltage needs to be greater than the enable threshold

and the VIN voltage needs to be higher than the UVLO.

The higher of the two voltages, which is the UVLO,

determines the turn on time. At turn- off, the first

condition of either enable threshold low or the VIN UVLO

will determine the turn-off event.

After the enable goes high, the IC has a delay time before

the output voltage ramps up. The delay is typically

between 120µs to 510µs. The 510µs is related to the lower

VIN condition.

With a 1

μF output capacitor (capacitor part

number: GRM155R61A105kE15) at no load conditions,

the output voltage ramp time is typically at 15µs. The

device has an internal discharge MOSFET to discharge

the output voltage when the enable pin is asserted low;

the typical discharge time is at 2ms. The enable and

disable waveforms are illustrated in Figure 1, and the

Oscilloscope waveform is shown in the Typical

Characteristics.

Figure 1: Timing Diagram

The Output Noise

LDO noise generally is characterized through noise

spectral density (NSD) and total RMS value in the

frequency band between 10Hz to 100kHz. The noise

spectral density can be measured using a network

analyzer with active probes. The RMS noise value is

obtained from the noise spectral density curve by taking

the square root of the area within the frequency range

from 10Hz to 100kHz.

The normalized output noise for SC573 is at a typical

value of 100µVRMS/V. The generalized output voltage

noise can be approximated by: V

RMS=VOUT*100 µV.

Protection Features

SC573 provides protection features to ensure that no

damage is incurred in the event of a fault condition. These

functions include:

• Under-Voltage Lockout

• Over-Temperature Protection

• Short-Circuit Protection with peak and fold-

back current limit

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