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SC4215J

Very Low Input / Very Low Dropout 2 Amp Regulator With Soft-Start

Semtech Corporation 

SC4215J

Applications Information

Introduction

The SC4215J is intended for applications where high

current capability and very low dropout voltage are

required. It provides a very simple, low cost solution that

uses very little PCB area. Additional features include an

enable pin to allow for a very low power consumption in

standby mode, and a fully adjustable output.

Noise Immunity

In very electrically noisy environments, it is recommended

that 0.1µF ceramic capacitors be placed from VIN to GND

and VO to GND as close to the device pins as possible.

VO Setting: VO=VREF

By connecting the FB pin directly to the VO pin, the output

voltage will be regulated to the 0.5V internal reference.

device being some distance from any bulk capacitance on

the rail. Additionally, the input droop due to load tran-

sients is reduced, improving load transient response.

Additional capacitance may be added if required by the

application.

Output Capacitor

A minimum bulk capacitance of 10µF/A (output load),

along with a 0.1µF ceramic decoupling capacitor is recom-

mended. For VO less than 0.6V, a minimum bulk capaci-

tance of 40µF, along with a 0.1µF ceramic decoupling

capacitor is recommended. The use of multiple lower

value ceramic capacitors in parallel to achieve the desired

bulk capacitance will not cause stability issues. Although

designed for use with ceramic output capacitors, the

SC4215J is extremely tolerant of output capacitor ESR

values and thus will also work comfortably with tantalum

output capacitors.

VO Setting with External Resistors

The use of 1% resistors, and designing for a current flow ≥

10µA is recommended to ensure a well regulated output

(thus R2 ≤50kΩ). A suitable value for R2 can be chosen in

the range of 1kΩ to 50kΩ. R1 can then be calculated from.

( ) 5 =5 ⋅

92 − 95()

95()

Enable

Pulling this pin below 0.4V turns the regulator off, reduc-

ing the quiescent current to a fraction of its operating

value. Driving this pin high enables the regulator. A pull

up resistor up to 400kOhms should be connected from

this pin to the VIN pin in applications where the Enable

pin is not driven from a control circuit.

Input Capacitor

A large bulk capacitance ≥ 10µF/A (output load) should be

placed close to the input supply pin of the SC4215J to

ensure that VIN does not drop below the minimum VIN. Also

a minimum of 4.7µF ceramic capacitor is recommended to

be placed directly next to the VIN pin. This allows for the

Soft-Start

The soft-start is achieved by using a voltage ramp as the

voltage reference for the internal error amplifier during

startup. This voltage ramp is created by an internal current

source charging an internal soft-start capacitor. When the

voltage ramp reaches 500mV, the voltage reference for

the internal error amplifier switches to the fixed 500mV

VREF. Thus, during soft-start, the output tracks the internal

voltage ramp, which limits the input inrush current and

provides a programmed soft-start profile for a wide range

of applications.

Over-Current and Thermal Shutdown

The over-current protection and thermal shutdown func-

tions protect the regulator against damage due to exces-

sive power dissipation. The SC4215J is designed to current

limit when the output current reashes 3A (typical). When

the load exceeds 3A, the output voltage is reduced to

maintain a constant current limit.

The thermal shutdown function limits the junction tem-

perature to a maximum of 160OC (typical). Thermal shut-

down turns off the regulator as the junction temperature

begins to exceed 160OC. When the junction temperature



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