GM1117S-ATC3T 데이터 시트보기 (PDF) - Gamma Microelectronics Inc.

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GM1117S-ATC3T

1A LOW DROPOUT PRECISION VOLTAGE REGULATOR

Gamma Microelectronics Inc. 

GM1117S

1A LOW DROPOUT

PRECISION VOLTAGE REGULATOR

Heatsink Requirements

When an integrated circuit operates with an appreciable current, its junction temperature is elevated.

It is important to consider its thermal limits in order to achieve acceptable performance and reliability.

This limit is determined by summing the individual parts consisting of a series of temperature rises

from the semiconductor junction to the operating environment.

The heat generated at the device junction flows through the die to the die attach pad, through the

lead frame to the surrounding case material, to the printed circuit board, and eventually to the

ambient environment. Below is a list of variables that may affect the thermal resistance and in turn

the need to a heatsink.

ΘJC, Junction to Case Thermal Resistance ΘCA, Case to Ambient Thermal Resistance

1. Lead Frame Size & Material

1. Mounting Pad Size, Material & Location

2. Number of conducting Pins

2. Placement of Mounting Pad

3. Die Size

3. PCB Size & Material

4. Die Attach Material

4. Traces Length & Width

5. Molding Compound Size & Material

5. Adjacent Heat Source

6. Volume of Air

7. Ambient Temperature

8. Shape of Mounting Pad

The GM1117S regulators have internal thermal shutdown to protect the device from over heating.

Under all possible operating conditions, the junction temperature of the GM1117S must be within in

the range of 0°C to 125°C. A heatsink may be required depending on the maximum power

dissipation and maximum ambient temperature of the application. To determine if a heatsink is

needed, the power dissipated y the regulator, PD, must be calculated according to the circuit below:

GM1117S

IIN

VIN

VIN VOUT

Gnd

VOUT

IL

IIN = IL + IG

PD = (VIN – VOUT) X IL + VIN X IG

IG

The next parameter which must be calculated is the maximum allowable temperature rise, TR(max):

TR(max) = TJ(max) – TA(max)

Where TJ(max) is the maximum allowable junction temperature (125°C) and TA(max) is the maximum

ambient temperature which will be encountered in the application.

Using the calculated values for TR(max) and PD the maximum allowable value for the junction-to-ambient

thermal resistance (θJA) can be calculated:

ΘJA(max) = TR(max) X PD

If the maximum allowable value for ΘJA is found to be > 136°C/W for SOT223 packages or > 79°C/W

for TO220 package or > 92°C/W for TO252 package, no heat sink is needed since the package

alone will dissipate enough heat to satisfy these requirements. If the calculated value for ΘJA falls

below these limits, a heat sink is required.

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