SC561 datasheet(11/15 Pages) SEMTECH

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SC561

Applications Information (continued)

Protection Features

The SC561 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

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

drops below the UVLO threshold, as defined

in the Electrical Characteristics section, the LDOs are

disabled and PGOOD is held low. The LDOs are re-enabled

into their previous states when VIN is increased above the

hysteresis level. When powering up with V

below the

UVLO threshold, the LDOs remain disabled and PGOOD is

held low.

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 both LDO outputs and holds the

PGOOD signal low. The LDOs can only be re-enabled by

cycling the EN pin.

•

Short-Circuit Protection

Each 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 load

current returns to a specified level.

Component Selection

A minimum capacitance of 1μF on each output is required

to ensure stability. This must be considered when

choosing very small size capacitors as the dc bias must

be included in their derating to ensure this required value.

For example, a 1μF 0402 size capacitor may work at low

output voltages, but the capacitance may be too low at

higher output voltages. 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. It is also recommended that the input be

bypassed with a 2.2μF, low ESR X5R or X7R capacitor to

minimize noise and improve transient response. Note:

Tantalum and Y5V capacitors are not recommended.

The BYP pin on the SC561 must have a minimum of 22nF

connected to ground to meet all noise-sensitive require-

ments. This value can be increased to a maximum of 1μF

to improve noise and PSRR. However, larger values of

bypass capacitor will increase the start-up time of the

SC561.

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