SC1564 データシートの表示（PDF） - Semtech Corporation

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SC1564

Low Dropout 600mA Linear Regulator in 3mm x 3mm Package

Semtech Corporation 

SC1564

Applications Information

Introduction

Thermal Considerations

The SC1564 is intended for applications such as graph-

ics cards where high current capability and low drop-

out voltage are required. It provides a very simple, low

cost solution that uses little PCB real estate. Additional

features include a shutdown pin to allow for a very low

power consumption standby mode, and a fully adjust-

able output.

Component Selection

Input capacitor: A 1µF ceramic capacitor is recommended.

This allows for the device some distance 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 1µF,

along with a 0.1µF ceramic decoupling capacitor, is rec-

ommended. 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 ceramic output capacitors, the

SC1564 is extremely tolerant of output capacitor ESR

values and thus will also work comfortably with tantalum

output capacitors.

Noise immunity: In very electrically noisy environents, 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.

The power dissipation in the SC1564 is approximately

equal to the product of the output current and the input

to output voltage differential:

PO (VIN  VOUT ) ˜ IOUT

The absolute worst-case dissipation is given by:

PO(MAX) = ( VIN(MAX) − V ) ⋅ I OUT(MIN) OUT(MAX) + VIN(MAX) ⋅ IQ(MAX)

For a typical scenario, VIN = 3.3V ± 5%, VOUT = 1.5V and

IOUT = 600mA, therefore:

VIN(MAX) = 3.465V,

VOUT(MIN) = 1.47V and

IQ(MAX) = 170µA,

Thus PD(MAX) = 1.1976W.

Using this figure, and assuming TA(MAX) = 85°C, we can

calculate the maximum thermal impedance allowable

to maintain TJ ≤ 150°C:

R TH(JA)(MAX)

¨¨©§

T  T J(MAX)

A(MAX)

PO(MAX)

¸¸¹·

¨©§

150qC  85qC

1.1976W

¸¹·

54.3qC W

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

package using PCB copper area to aid in conducting the

heat away from the device. Internal ground/power planes

and air flow will also assist in removing heat.

External voltage selection resistors: the use of 1% resis-

tors, designed for a current flow ≥ 10µA is recommended

to ensure a well-regulated output (tus, R2 ≤ 120kΩ).



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