SC563 datasheet(13/16 Pages) SEMTECH

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SC563

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 V

IN drops below the UVLO threshold, as

defined in the Electrical Characteristics section, the

corresponding LDO is disabled. The LDO is re-enabled

when V

IN is increased above the hysteresis level. When

powering up with V

IN below the UVLO threshold, the LDO

remains disabled.

Over-Temperature Protection

Over-Temperature protection are separately available on

both LDOs.

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 tempera-

ture drops below its hysteresis value, the LDO output will

resume.

Short-Circuit Protection

Each 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

SC563 is designed for PCB savings with small area. The

recommended input and output capacitor is μF with

0402 package with part number GRM55R6A05kE5.

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 0μF. 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 each of the two LDOs in the SC563 can provide

300mA of output current, the maximum power dissipation

in the device is restricted by the miniature package size.

The graphs in Figures 2 can be used as a guideline to

determine whether the input voltage, output voltages,

output currents, and ambient temperature of the system

result in power dissipation within the operating limits are

met or if further thermal relief is required.

0.5

1.5

2.5

-50

-35

-20

-5

100

Ambient Temperature (C)

TJ=150°C

TJ=125°C

TJ=105°C

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 SC563 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)

D = Power Dissipation (W)

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

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