SC4212 データシートの表示（PDF） - Semtech Corporation

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SC4212

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

Semtech Corporation 

SC4212

Applications Information

Introduction

The SC4212 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 real estate. Additional features

include an enable pin to allow for a very low power con-

sumption standby mode, and a fully adjustable output.

Component Selection

where an input voltage of < 1.9V is required. For applica-

tions with input voltages higher than 1.9V, the EN pin

could be left open or connected to VIN.

Thermal Considerations

The power dissipation in the SC4212 is approximately

equal to the product of the output current and the

input to output voltage differential:

Input capacitor: A large bulk capacitance of ≥ 10μF

should be placed close to the input supply pin of the

SC4212 to ensure that VIN does not sag below 1.5V. Also

a minimum 4.7μF ceramic capacitor is recommended

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

for the device being some distance fromany 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 re-

quired by the application.

Output capacitor: A minimum bulk capacitance of ≥

10μF, along with a 0.1μF ceramic decoupling capacitor

is recommended. Increasing the bulk capacitance will

improve the overall transient response.The use of mul-

tiple 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 SC4212 is extremely tolerant 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 0.1 μF ceramic capacitors be

placed from VIN to GND and VOUT to GND as close to the

device pins as possible.

P = (V - V ) x I

O

IN OUT OUT

The absolute worst-case dissipation is given by:

P =V -V )xI

+V xI

O(MAX) IN(MAX) OUT(MIN) OUT(MAX) IN(MAX) Qt(MAX)

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

IOUT = 1A, therefore:

VIN(MAX) = 3.465V,

VOUT = 2.744V and

(MIN)

I = 3mA

Q(MAX)

Thus P = 0.731W.

D(MAX)

Using this figure, and assuming T = 70°C, we can

A(MAX)

calculate the maximum thermal impedance allowable

to

maintain

T

J

≤

125°C:

R TH(J −A)(MAX)

=

¨¨©§

T − T J(MAX) A(MAX)

PO(MAX)

¸¸¹·

=

¨§125°C − 85°C

© 0.722W

¸·

¹

=

76 °C

W

This should be achievable with the 3mm x 3mm MLPD-8

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 tempertures it may be necessary to use

additional copper area.

External voltage selection resistors: The use of 1%

resistors is recommended.

Enable: Pulling the EN pin below 0.5V turns the regula-

tor off, reducing the quiescent current to a fraction of its

operating value. A pull up resistor up to 400kΩ should be

connected from the EN pin to the VIN pin in application

7

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