SC4211EVB データシートの表示（PDF） - Semtech Corporation

部品番号

コンポーネント説明

一致するリスト

SC4211EVB

Very Low Input /Very Low Dropout 1 Amp Regulator With Enable

Semtech Corporation 

SC4211

POWER MANAGEMENT

Applications Information

Introduction

The SC4211 is intended for applications where high cur-

rent capability and very low dropout voltage are required.

It provides a very simple, low cost solution that uses very

little PCB real estate. Additional features include an en-

able pin to allow for a very low power consumption standby

mode, and a fully adjustable output.

Component Selection

Input capacitor: A large bulk capacitance of about

≥ 10uF/A (output load) should be closely placed to the

input supply pin of the SC4211 to ensure that Vin does

not sag below 1.4V. Also a minimum of 4.7µF ceramic

capacitor is recommended to be placed directly next to

the Vin pin. This allows for the device being some dis-

tance from any bulk capacitance on the rail. Additionally,

input droop due to load transients 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 de-

coupling capacitor is recommended. Increasing the bulk

capacitance will improve the overall transient response.

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 ce-

ramic output capacitors, the SC4211 is extremely toler-

ant of output capacitor ESR values and thus will also

work comfortably with tantalum output capacitors.

Noise immunity: In very electrically noisy environments,

it is recommended that 0.1µF ceramic capacitors be

placed from IN to GND and OUT to GND as close to the

device pins as possible.

Internal voltage selection: By connecting the FB pin to

GND, an internal resistor divider will regulate the output

voltage to 1.0V. If the FB pin is connected directly to the

VO pin, the output voltage will be regulated to the 0.5V

internal reference.

Enable: Pulling this pin below 0.4V turns the regulator

off, reducing the quiescent current to a fraction of its

operating value. A pull up resistor up to 400kOhms should

be connected from this pin to the VIN pin in application

where supply voltages of Vin < 1.9V is required. For ap-

plications with higher voltages than 1.9V, EN pin could

be left open or connected to VIN.

Thermal Considerations

The power dissipation in the SC4211 is approximately

equal to the product of the output current and the input

to output voltage differential:

PD ≈ (VIN − VOUT )• I O

The absolute worst-case dissipation is given by:

( ) PD(MAX) = VIN (MAX) − VOUT (MIN) • I O(MAX) + VIN (MAX) • I Q(MAX)

For a typical scenario, V = 3.3V ± 5%, V = 2.8V and

IN

OUT

I = 1A, therefore:

O

VIN(MAX) = 3.465V, VOUT(MIN) = 2.744V and IQ(MAX) = 1.75mA,

Thus P = .722W.

D(MAX)

Using this figure, and assuming TA(MAX) = 70°C, we can cal-

culate the maximum thermal impedance allowable to main-

tain

T

J

≤

150°C:

( ) ( ) R = TH(J−A)(MAX)

TJ(MAX) − TA(MAX)

PD(MAX)

=

150 − 70

.722

= 110°C/W

This should be achievable for the SOIC-8-EDP package

using PCB copper area to aid in conducting the heat away,

such as one square inch of copper connected to the ground

pins of the device. Internal ground/power planes and air

flow will also assist in removing heat. For higher ambient

temperatures it may be necessary to use additional cop-

per area.

External voltage selection resistors: The use of 1%

resistors, and designing for a current flow ≥ 10µA is

recommended to ensure a well regulated output (thus

R2 ≤ 50kΩ).

 2007 Semtech Corp.

7

www.semtech.com

Share Link: