SC3102

the output voltage drops below 10% of nominal, the

PGOOD pin is pulled low after a 20μs delay. During start-

up, PGOOD will be asserted 2ms (typical) after the output

voltage reaches 90% of the final regulation voltage. The

faults of over voltage, fold-back current limit mode and

delay. When recovering from a fault, PGOOD will be

asserted 2ms (typical) after Vout reaches 90% of the final

regulation voltage.

Enable

The EN input is used to enable or disable the device when

the device is not in UVLO. When EN is low (grounded), the

device enters shutdown mode and consumes less than

1μA of current. In shutdown mode, the device tri-states

the LX pin and pulls down the SS pin. The EN pin has a

500kΩ internal pull-down resistor. This resistor is switched

in circuit whenever the EN pin is below its threshold, or

when the device is in under voltage lockout and AVIN

exceeds 0.8V. When the device is enabled, it takes about

50μs for the internal circuitry to wake up and begin the

soft-start sequence.

100% Duty-Cycle Operation

The SC3102 is capable of operating at 100% duty-cycle.

When the difference between the input voltage and

output voltage is less than the minimum dropout voltage,

the PMOS switch turns completely on, operating in 100%

duty-cycle. The minimum dropout voltage is the output

current multiplied by the on-resistance of the internal

PMOS switch and the DC-resistance of the inductor when

the PMOS switch is on continuously.

Output L-C filter Selection

The SC3102 has fixed internal loop-gain compensation. It

is optimized for X5R or X7R ceramic output capacitors and

an output L-C filter corner frequency of less than 34kHz.

The output L-C corner frequency can be determined by

Equation 2.

In general, the inductor is chosen to set the inductor ripple

current to approximately 30% of the maximum output

current. It is recommended to use a typical inductor

value of 1μH to 2.2μH with output ceramic capacitors of

44μF or higher. Lower inductance should be considered

Applications Information (continued)

in applications where faster transient response is

required. More output capacitance will reduce the output

deviation for a particular load transient. When using low

inductance, the maximum peak inductor current at any

condition (normal operation and start up) can not exceed

2.5A which is the guaranteed minimum current limit. The

saturation current rating of the inductor needs to be at

least larger than the peak inductor current which is the

maximum output current plus half of the inductor ripple

current.

14

OUT

C

C

L

f

⋅

=

π

2

1

(2)