SC573 datasheet(13/17 Pages) SEMTECH

13 / 17 page

SC573

Final Rev2.1

Applications Information (continued)

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 either VIN drops below the UVLO threshold, as

defined in the Electrical Characteristics section, the LDO

is disabled. The LDO is re-enabled when VIN is increased

above the hysteresis level. When powering up with VIN

below the UVLO threshold, the LDO remains disabled.

Over-Temperature Protection

An internal Over-Temperature (OT) protection circuit

monitors the internal junction temperature. When the

temperature exceeds the OT threshold as defined in the

Electrical Characteristics section, the OT protection dis-

ables the corresponding LDO output. When the

temperature drops below its hysteresis value, the LDO

output will resume.

Short-Circuit Protection

The output has short-circuit protection with peak current

limit and fold back current limit. If the output current

exceeds the peak current limit, the output voltage will

drop and the output current will be limited to its fold

back current limit value. See the waveforms in the typical

operation section. If the short circuit is removed or the

load current reduces to below the fold back current limit,

the LDO output will rise back into regulation.

Component Selection

SC573 is designed to minimize the PCB solution area.

The recommended input and output capacitors are 1μF

with 0402 package, part number GRM155R61A105kE15.

Although there is no maximum value of output capacitor

specified, very large values may increase the rise time of

the output voltages without affecting stability. It is

recommended that the value of output capacitance be

restricted to a maximum of 10μF. Ceramic capacitors of

type X5R or X7R should be used because of their low ESR

and stable temperature coefficients. Tantalum capacitors

and Y5V capacitors are not recommended.

Thermal Considerations

Although SC573 can provide 300mA of output current,

the maximum power dissipation in the device is restricted

by the miniature package size. The graph in Figure 2 can

be used as a first-order guideline to determine whether

the input voltage, output voltage, output current, and

ambient temperature of the system result in power

dissipation within operating limits.

Figure 2: Maximum P

D vs. TA

The following procedure can be followed to determine if

the thermal design of the system is adequate. The junc-

tion temperature of the SC573 can be determined in

known operating conditions using the following

equation:

J = TA +(PD x θJA)

where

J = Junction Temperature (°C)

A = Ambient Temperature (°C)

θJA = Thermal Resistance Junction to Ambient (°C/W)

D = Power Dissipation (W)

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