HEATSINK SELECTION FOR LOW DROPOUT REGULATORS March 9, 1998 AN96-2 TEL:805-498-2111 FAX:805-498-3804 WEB:http://www.semtech.com Introduction Detailed Calculations For θs-a A crucial part of the overall design in a system incorporating a linear regulator is dissipating the heat that is generated in the regulator. This application note gives advice on choosing a heatsink and suitable part numbers from leading manufacturers. The required thermal impedance (sink-to-ambient) for any application is defined by the following equation:- θs − a = Tj − Ta − θj − c − θc − s P (1) Selecting a Heatsink 1. On the chart for the device that you are planning to Where: use, cross reference the maximum current required and (2) the system’s maximum ambient temperature. θs-a = thermal impedance sink-to-ambient (°C/W) 2. Read the required heatsink thermal impedance (sink- Tj to-ambient) off the chart. If your plotted point is between two lines, use the lower thermal impedance value. Ta 3. Look up your required thermal impedance value in Table 1: Suggested Heatsink Selection, ensuring that θj-c you use the column relevant to the air flow in your application. If the air flow in your application is between two of the values, then the lower flow rate column must be θ c-s used. From this table you can obtain suggested part numbers for three different manufacturers. Notes 1. These charts apply to heatsinking TO-220 regulators converting from 5V to 3.3V only. Please refer to the next column for information on how to calculate the heatsink requirements for other applications. 2. Note that if the device is mounted with no insulation, the heatsink will be smaller, less hardware will be used, and therefore the cost will be lower! Remember that in this case, the heatsink will be at the same potential as the output of the regulator. In cases with very high power dissipation, using insulation may not be an option. In extreme cases, consider using one of Semtech’s switching solutions, or the EZ1900 Load Balance Controller to enable the use of two smaller heatsinks. P = maximum junction temperature (°C) (obtained from the device data sheet) = maximum ambient temperature (°C) = thermal impedance junction-to-case (°C/W) (obtained from the device data sheet) = thermal impedance case-to-sink (°C/W) (look up in your thermal management hardware supplier’s data - for the TO-220 package, typically 1.25°C/W using silicone pads, and 0.5°C/W using thermal grease with no insulation ) = power dissipated in the device (W) (where P = IOUT(max)(VIN(max)-VOUT(min)) for worst case calculation) 1 © 1998 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320 HEATSINK SELECTION FOR LOW DROPOUT REGULATORS AN96-2 March 9, 1998 Heatsink for EZ1086CT Heatsink Thermal Impedance (Sink-to-Ambient) vs. Ambient Temperature and Output Current o Device mounted using thermal grease with no insulation on unfinished aluminum (θc-s = 0.5 C/W) 2.5 Output Current (A) 2 B 1.5 C D A = 50 C/W B = 20 C/W C = 17.5 C/W D = 15 C/W 1 A: No Heatsink 0.5 0 25 45 65 85 105 125 Ambient Temperature (oC) Heatsink Thermal Impedance (Sink-to-Ambient) vs. Ambient Temperature and Output Current o Device mounted using a silicone pad (θc-s = 1.25 C/W) 2.5 Output Current (A) 2 B 1.5 C D A = 50 C/W B = 20 C/W C = 17.5 C/W D = 15 C/W 1 A: No Heatsink 0.5 0 25 45 65 85 105 125 Ambient Temperature (oC) Note: these charts valid for 5V to 3.3V conversion only © 1998 SEMTECH CORP. 2 652 MITCHELL ROAD NEWBURY PARK CA 91320 HEATSINK SELECTION FOR LOW DROPOUT REGULATORS AN96-2 March 9, 1998 Heatsink for EZ1085CT and EZ1587CT Heatsink Thermal Impedance (Sink-to-Ambient) vs. Ambient Temperature and Output Current o Device mounted using thermal grease with no insulation on unfinished aluminum (θc-s = 0.5 C/W) 3.5 C 3 D E F B 2.5 Output Current (A) A A = 20 C/W B = 17.5 C/W 2 C = 15 C/W D = 12.5 C/W E = 10 C/W 1.5 F = 7.5 C/W 1 0.5 0 25 45 65 85 105 125 Ambient Temperature (oC) Heatsink Thermal Impedance (Sink-to-Ambient) vs. Ambient Temperature and Output Current o Device mounted using a silicone pad (θc-s = 1.25 C/W) 3.5 C 3 D E F G B 2.5 A A = 20 C/W Output Current (A) B = 17.5 C/W C = 15 C/W 2 D = 12.5 C/W E = 10 C/W F = 7.5 C/W G = 5 C/W 1.5 1 0.5 0 25 45 65 85 105 125 Ambient Temperature (oC) Note: these charts valid for 5V to 3.3V conversion only © 1998 SEMTECH CORP. 3 652 MITCHELL ROAD NEWBURY PARK CA 91320 HEATSINK SELECTION FOR LOW DROPOUT REGULATORS AN96-2 March 9, 1998 Heatsink for EZ1084CT and EZ1087CT Heatsink Thermal Impedance (Sink-to-Ambient) vs. Ambient Temperature and Output Current o Device mounted using thermal grease with no insulation on unfinished aluminum (θc-s = 0.5 C/W) 6 D 5 E F C 4 A = 15 C/W Output Current (A) B B = 12.5 C/W C = 10 C/W A D = 7.5 C/W 3 E = 5 C/W F = 2.5 C/W 2 1 0 25 45 65 85 105 125 Ambient Temperature (oC) Heatsink Thermal Impedance (Sink-to-Ambient) vs. Ambient Temperature and Output Current o Device mounted using a silicone pad (θc-s = 1.25 C/W) 6 D 5 E F C Output Current (A) 4 A = 15 C/W B = 12.5 C/W B C = 10 C/W A D = 7.5 C/W 3 E = 5 C/W F = 2.5 C/W 2 1 0 25 45 65 85 105 125 Ambient Temperature (oC) Note: these charts valid for 5V to 3.3V conversion only © 1998 SEMTECH CORP. 4 652 MITCHELL ROAD NEWBURY PARK CA 91320 HEATSINK SELECTION FOR LOW DROPOUT REGULATORS AN96-2 March 9, 1998 Heatsink for EZ1083CT Heatsink Thermal Impedance (Sink-to-Ambient) vs. Ambient Temperature and Output Current o Device mounted using thermal grease with no insulation on unfinished aluminum (θc-s = 0.5 C/W) 8 D E F 7 6 C Output Current (A) A = 12.5 C/W 5 B = 10 C/W B C = 7.5 C/W D = 5 C/W E = 2.5 C/W 4 F = 1 C/W A 3 2 1 0 25 45 65 85 105 125 Ambient Temperature (oC) Heatsink Thermal Impedance (Sink-to-Ambient) vs. Ambient Temperature and Output Current o Device mounted using a silicone pad (θc-s = 1.25 C/W) 8 E F D 7 6 C A = 12.5 C/W B = 10 C/W Output Current (A) 5 C = 7.5 C/W D = 5 C/W B E = 2.5 C/W 4 F = 1 C/W A 3 2 1 0 25 45 65 85 105 125 Ambient Temperature (oC) Note: these charts valid for 5V to 3.3V conversion only © 1998 SEMTECH CORP. 5 652 MITCHELL ROAD NEWBURY PARK CA 91320 HEATSINK SELECTION FOR LOW DROPOUT REGULATORS AN96-2 March 9, 1998 Heatsink for EZ1082CT Heatsink Thermal Impedance (Sink-to-Ambient) vs. Ambient Temperature and Output Current o Device mounted using thermal grease with no insulation on unfinished aluminum (θc-s = 0.5 C/W) 11 E 10 F 9 D 8 A = 12.5 C/W Output Current (A) 7 B = 10 C/W C = 7.5 C/W C D = 5 C/W 6 E = 2.5 C/W F = 1 C/W 5 B 4 A 3 2 1 0 25 45 65 85 105 125 Ambient Temperature (oC) Heatsink Thermal Impedance (Sink-to-Ambient) vs. Ambient Temperature and Output Current o Device mounted using a silicone pad (θc-s = 1.25 C/W) 11 E 10 F G 9 8 A = 12.5 C/W D B = 10 C/W Output Current (A) 7 C = 7.5 C/W D = 5 C/W 6 E = 2.5 C/W C F = 1 C/W 5 G = 0.5 C/W B 4 A 3 2 1 0 25 45 65 85 105 125 Ambient Temperature (oC) Note: these charts valid for 5V to 3.3V conversion only © 1998 SEMTECH CORP. 6 652 MITCHELL ROAD NEWBURY PARK CA 91320 HEATSINK SELECTION FOR LOW DROPOUT REGULATORS AN96-2 March 9, 1998 Table 1: Suggested Heatsink Selection Heatsink θs-a (°C/W) Mfr. 20 17.5 15 12.5 10 7.5 5 2.5 1 (1) Forced Air Cooling None (Convection Only) (2) 100 Linear Feet Per Minute (2) A 574802 T 6038B W 297-V2-80B (2) 574802 (2) 574802 (2) (2) 6038B (2) 800 Linear Feet Per Minute 6038B (2) 297-V2-80B (2) (2) 297-V2-80B (2) 574802 A 575002 574802 T 6021PB 6038B W 286-AB 297-V2-80B A 575002 574802 574802 T 6021PB 6021PB 6038B W 286-AB A 513102 575002 574802 T 6099B 6021PB 6038B W 627-15ABP 286-AB 297-V2-80B A 513202 575002 574802 T 6100B 6021PB 6038B W 627-20ABP 286-AB 297-V2-80B A 532602 513302 574802 T 6298B 6101B 6038B W 657-15ABP 627-25ABP 297-V2-80B A 532702 513302 574802 T 6299B 6101B 6021PB W 657-20ABP 627-25ABP 286-AB A Not Applicable 532802 513002 T 6400B 6098B W 677-25ABP 627-10ABP A Not Applicable 532802 (2) (2) 6038B (2) (2) (2) 297-V2-80B (2) (2) (2) 297-V2-80B (2) 297-V2-80B (2) (2) (2) (2) (2) (2) (2) (2) (2) (2) T 6300B W 657-25ABP 0.5 Specialized Solutions Only Notes: 1. Manufacturer: A = Aavid Engineering, Inc. T = Thermalloy, Inc. W = Wakefield Engineering 2. No additional hardware required for these heatsinks (other than insulators/thermal grease as needed) © 1998 SEMTECH CORP. 7 652 MITCHELL ROAD NEWBURY PARK CA 91320