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GM1117S-2.5TA3R Datasheet(PDF) 11 Page - Gamma Microelectronics Inc. |
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GM1117S-2.5TA3R Datasheet(HTML) 11 Page - Gamma Microelectronics Inc. |
11 / 15 page 11 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 2. Number of conducting Pins 3. Die Size 4. Die Attach Material 5. Molding Compound Size & Material 1. Mounting Pad Size, Material & Location 2. Placement of Mounting Pad 3. PCB Size & Material 4. Traces Length & Width 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: IIN = IL + IG PD = (VIN – VOUT) X IL + VIN X 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. VIN VOUT GM1117S VIN VOUT Gnd IG IL IIN |
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