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 2007 Semtech Corp.

www.semtech.com

SC4215A

POWER MANAGEMENT

Introduction

The SC4215A 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 SC4215A to ensure that Vin does not sag below

1.4V. Also a minimum of 4.7µF ceramic capacitor is rec-

ommended to be placed directly next to the Vin pin. This

allows for the device being some distance from any bulk

capacitance on the rail. Additionally, input droop due to

load transients is reduced, improving load transient re-

sponse. 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 SC4215A is extremely tol-

erant 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 1.2V.

If the FB pin is connected directly to the VO pin, the out-

put voltage will be regulated to the 0.5V internal refer-

ence.

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).

Applications Information

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 SC4215A is approximately

equal to the product of the output current and the input to

output voltage differential:

()

O

D

I

VOUT

VIN

P

•

−

≈

The absolute worst-case dissipation is given by:

()

Q(MAX)

(MAX)

O(MAX)

(MIN)

(MAX)

D(MAX)

I

VIN

I

VOUT

VIN

P

•

+

•

−

=

For a typical scenario, V

I

V

Thus P

Using this figure, and assuming T

culate the maximum thermal impedance allowable to main-

tain T

C/W

110

.722

70

150

P

T

T

R

D(MAX)

A(MAX)

J(MAX)

A)(MAX)

TH(J

°

=

−

=

−

=

−

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 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.