SC4216(2006) 데이터 시트보기 (PDF) - Semtech Corporation

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SC4216
(Rev.:2006)

Very Low Input/Very Low Dropout 3 Amp Regulator With Enable

Semtech Corporation 

SC4216

POWER MANAGEMENT

Applications Information

Introduction

The SC4216 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 ≥ 10µF/A (out-

put load) should be closely placed to the input supply pin

of the SC4216 to ensure that Vin does not sag below 1.45V.

Also a minimum of 4.7µF ceramic capacitor is recom-

mended to be placed directly next to the Vin pin. This al-

lows for the device being some distance from any bulk ca-

pacitance 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 par-

allel to achieve the desired bulk capacitance will not cause

stability issues. Although designed for use with ceramic

output capacitors, the SC4216 is extremely tolerant of out-

put capacitor ESR values and thus will also work comfort-

ably 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 1.2V. 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 operat-

ing 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 applications

with higher voltages than 1.9V, EN pin could be left open

or connected to VIN.

Thermal Considerations

The power dissipation in the SC4216 is approximately equal

to the product of the output current and the input to out-

put voltage differential:

PD ≈ (VIN − VOUT )• IO

The absolute worst-case dissipation is given by:

( ) PD (MAX ) = VIN (MAX ) − VOUT (MIN ) • IO (MAX ) + VIN (MAX ) • IQ (MAX )

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

IO = 1.5A, therefore:

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

Thus PD(MAX) = 1.09W.

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

culate the maximum thermal impedance allowable to main-

tain TJ ≤ 150°C:

( ) R = TH(J− A )(MAX )

TJ(MAX ) − TA (MAX )

PD (MAX )

=

(150 − 70)

1.09

=

73.4° C

/

W

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

ing pcb copper area to aid in conducting the heat away,

such as one square inch of copper connected to the ex-

posed die pad 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 addi-

tional copper 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).

 2006 Semtech Corp.

7

www.semtech.com

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