AND9008/D Thermal Considerations for the ON Semiconductor Family of Discrete Constant Current Regulators (CCR) in DPAK, SMC and SMB packages for Driving LEDs http://onsemi.com APPLICATION NOTE Prepared by: Mike Sweador and David Helzer ON Semiconductor ±10% and 20 mA ±15% with a higher breakdown voltage of 120 V. See appendix A for device list. Introduction: This application note supplements AND8391/D adding thermal information for DPAK, SMB and SMC packages and includes performance data for both FR4 and Thermal (aluminum backed) MCPCB ( Metal Clad PCB) material. The ON Semiconductor Constant Current Regulator (CCR) family of devices offers outstanding regulation for LEDs and other current based loads, such as battery charging circuits. The CCR reduces the complexity of resistor biased designs for sensitive loads, such as LED strings connected in series. The CCR can also be connected in parallel for higher load current applications. See application note AND8349/D for basic circuit considerations. The two−terminal CCR requires no external components to regulate at the specified current. The three−terminal device allows for current adjustment by using an external resistor. In the automotive lighting market (see app note AND8349/D), these devices can be used wherever a constant current is needed to maintain luminosity under varying voltage conditions. The purpose of this paper is to explore the temperature and power boundaries for devices in the DPAK, SMB and SMC package operating from typical currents of 50 mA to 350 mA in LED lighting applications. The DPAK adjustable devices available are rated at 60 mA to 100 mA and 90 mA to 160 mA. The fixed DPAK and SMC devices are rated at 350 mA. The SMB devices are rated at 50 mA ±10%, 30 mA © Semiconductor Components Industries, LLC, 2012 May, 2012 − Rev. 2 Reference to Data Sheet: The data sheet describes the devices and defines the following terms that will be used throughout this note: Vak = Voltage applied between the Anode and Cathode of the device. Ireg−ss = The current through the device supplied to the LEDs under steady−state operating conditions (device on ≥5 min.) Ireg−p = The current through the device supplied to the LEDs under pulse test conditions (≤ 300 msec). VR = Reverse Voltage PD = Device power dissipation, typically in mW. TA = Ambient Temperature in °C TJ = Device Junction Temperature in °C The DPAK adjustable CCR Data Sheet Thermal Characteristics table lists the thermal performance of each device as related to the heat spreader area and thickness. These datasheet tables and curves show thermal specifications and limits with the device junction temperature (TJ) operating at 150°C, the maximum allowable continuous junction temperature mounted on FR4 PCB material. Operating at TJ max continuously is not recommended for long term reliability. 1 Publication Order Number: AND9008/D AND9008/D THERMAL PERFORMANCE The following Figures (Figures 1 through 10) and Tables (Table 1 through 10) provide the typical thermal performance based on a single printed circuit board (PCB) operated in still air. Figure 1 shows power dissipation over changes in ambient temperature for the DPAK package on FR4 PCB material. Table 1 shows maximum power dissipation for a given heat spreader area at 85°C. These tables and graphs illustrate the effect of Cu area, thickness and also ambient temperature (TA ) over the range of −40°C to 85°C, which encompasses an area of interest for general LED operation. LED data sheets show an extreme reduction in luminosity above 85°C TA. Figure 1. DPAK Thermal FR4 PD vs TA for TJ of 1505C Table 1. PD max @ 855C DPAK 1000 mm 3 oz Cu 1821 mW 700 mm 2 oz Cu 1411 mW 700 mm 1 oz Cu 1201 mW 500 mm 2 oz Cu 1270 mW 500 mm 1 oz Cu 1082 mW 300 mm 2 oz Cu 1083 mW 300 mm 1 oz Cu 921 mW http://onsemi.com 2 AND9008/D Figure 2 shows power dissipation over changes in ambient temperature for the DPAK package on MCPCB material, Denka K1. Table 2 shows maximum power dissipation for a given heat spreader area at 85°C. These tables and graphs illustrate the effect of Cu area, thickness, clad material and ambient temperature (TA ) over the range of −40°C to 125°C, which encompasses an area of interest for general LED operation. Figure 2. DPAK MCPCB PD vs. TA for TJ = 1755C Table 2. PD max @ 855C DPAK 2500 mm2, Denka K1, 2 oz 6618 mW 1600 mm2, Denka K1, 2 oz 5202 mW 900 mm2, Denka K1, 2 oz 3830 mW 400 mm2, Denka K1, 2 oz 2486 mW 1000 mm2, FR4, 3 oz 2521 mW http://onsemi.com 3 AND9008/D Figure 3 is a comparison between power dissipation over changes in ambient temperature for the DPAK package on FR4 PCB material and MCPCB, Denka K1 material. Table 3 shows maximum power dissipation for a given heat spreader area at 85°C. The MCPCB affords a similar Power dissipation capability with a 60% decrease in area at 85°C for the same TJ. For HB (high brightness) LED’s, this is necessary for application space limitations. The form factor for existing lighting applications dictates the size of the LED and driver PCB. Figure 3. DPAK FR4 vs. MCPCB for TJ = 1505C and TJ = 1755C Compare Table 3. PD max @ 855C DPAK 400 mm2, Denka K1, 2 oz/175°C 2486 mW 400 mm2, Denka K1, 2 oz/150°C 1796 mW 1000 mm, FR4, 3 oz/175°C 2521 mW 1000 mm FR4, 3 oz/150°C 1821 mW http://onsemi.com 4 AND9008/D Figure 4 shows power dissipation over changes in ambient temperature for the SMC package on FR4 PCB material. Table 4 shows maximum power dissipation for a given heat spreader area at 85°C. These tables and graphs illustrate the effect of Cu area, thickness and also ambient temperature (TA ) over the range of −40°C to 85°C, which encompasses an area of interest for general LED operation. LED data sheets show an extreme reduction in luminosity above 85°C TA. Figure 4. SMC FR4 PCB PD vs. TA for TJ = 1755C Table 4. PD max @ 855C SMC 1000 mm, 3 oz Cu 1837 mW 700 mm, 2 oz Cu 1398 mW 700 mm, 1 oz Cu 1320 mW 500 mm, 2 oz Cu 1261 mW 500 mm, 1 oz Cu 1192 mW 300 mm, 2 oz Cu 1080 mW 300 mm, 1 oz Cu 1023 mW http://onsemi.com 5 AND9008/D Figure 5 shows power dissipation over changes in ambient temperature for the SMC package on MCPCB material, Denka K1. Table 5 shows maximum power dissipation for a given heat spreader area at 85°C. These tables and graphs illustrate the effect of Cu area, thickness, clad material and ambient temperature (TA ) over the range of −40°C to 125°C, which encompasses an area of interest for general LED operation. Figure 5. SMC MCPCB PD vs. TA for TJ = 1755C Table 5. PD max @ 855C 2500 mm2, SMC Denka K1, 2 oz 3516 mW 1600 mm2, Denka K1, 2 oz 3072 mW 900 mm2, Denka K1, 2 oz 2535 mW 400 mm2, Denka K1, 2 oz 1867 mW http://onsemi.com 6 AND9008/D Figure 6 is a comparison between power dissipation over changes in ambient temperature for the SMC package on FR4 PCB material and MCPCB, Denka K1 material. Table 6 shows maximum power dissipation for a given heat spreader area at 85°C. The MCPCB affords a similar Power dissipation capability with a 60% decrease in area at 85°C. For HB (high brightness) LED’s, this is necessary for application space limitations. The form factor for existing lighting applications dictates the size of the LED and driver PCB. Figure 6. SMC FR4 vs. MCPCB Compare PD vs. TA for TJ = 1755C Table 6. PD max @ 855C SMC 400 mm2, Denka K1, 2 oz 1867 mW 1000 mm, FR4, 3 oz 1837 mW http://onsemi.com 7 AND9008/D Figure 7 shows power dissipation over changes in ambient temperature for the SMB package on FR4 PCB material. Table 7 shows maximum power dissipation for a given heat spreader area at 85°C. These tables and graphs illustrate the effect of Cu area, thickness and also ambient temperature (TA ) over the range of −40°C to 85°C, which encompasses an area of interest for general LED operation. LED data sheets show an extreme reduction in luminosity above 85°C TA. Figure 7. SMB FR4 Thermal PD vs. TA for TJ of 1755C Table 7. PD max @ 855C SMB 700 mm, 2 oz Cu 1362 mW 700 mm, 1 oz Cu 1289 mW 500 mm, 2 oz Cu 1233 mW 500 mm, 1 oz Cu 1169 mW 300 mm, 2 oz Cu 1059 mW 300 mm, 1 oz Cu 1000 mW 100 mm, 2 oz Cu 769 mW 100 mm, 1 oz Cu 726 mW http://onsemi.com 8 AND9008/D Figure 8 shows power dissipation over changes in ambient temperature for the SMB package on MCPCB material, Denka K1. Table 8 shows maximum power dissipation for a given heat spreader area at 85°C. These tables and graphs illustrate the effect of Cu area, thickness, clad material and ambient temperature (TA ) over the range of −40°C to 85°C, which encompasses an area of interest for general LED operation. Figure 8. SMB MCPCB PD vs. TA for TJ of 1755C Table 8. PD max @ 855C SMB 900 mm, MC/2 oz 3000 mW 400 mm, MC/2 oz 2500 mW http://onsemi.com 9 AND9008/D Figure 9 is a comparison between power dissipation over changes in ambient temperature for the SMB package on FR4 PCB material and MCPCB, Denka K1 material. Table 9 shows maximum power dissipation for a given heat spreader area at 85°C. The MCPCB 400 mm2, 2 oz Cu affords a 10.1% increase in Power dissipation capability with a 43% decrease in area compared to FR4 700 mm2, 2 oz Cu at 85°C. For HB (high brightness) LED’s, this is necessary for application space limitations. The form factor for existing lighting applications dictates the size of the LED and driver PCB. TA °C Figure 9. SMB FR4 vs. MCPCB Compare PD vs. TA for TJ of 1755C Table 9. PD max @ 855C SMB 900 mm2, Denka K1, 2 oz 1800 mW 400 mm2, Denka K1, 2 oz 1500 mW 700 mm, FR4, 2 oz Cu 1362 mW 700 mm, FR4, 1 oz Cu 1289 mW http://onsemi.com 10 AND9008/D Figure 10 is a summary comparison between power dissipation over changes in ambient temperature for the DPAK, SMC and SMB packages on FR4 PCB material and MCPCB, Denka K1 material. This chart will assist in selection of circuit board material and size knowing the operating ambient temperature of a circuit and the maximum device power dissipation. Figure 10. Summary DPAK, SMC, SMB for T = 1755C Table 10. PD max @ 855C DPAK, SMC, SMB 400 mm2, Denka K1, 2 oz DPAK 2486 mW 400 mm2, Denka K1, 2 oz SMC 1867 mW 400 mm2, Denka K1, 2 oz SMB 1500 mW 1000 mm, FR4, 3 oz Cu DPAK 2521 mW 1000 mm, FR4, 3 oz Cu SMC 1837 mW 700 mm, FR4, 2 oz Cu SMB 1362 mW http://onsemi.com 11 AND9008/D Application Examples PC board design and the use of multilayer board material will affect the thermal performance. See ON Semiconductor application notes AND8220/D and AND8222/D for further information. Ambient operating temperature (TA) and estimated device power will help determine which package to use. The data provided in this application note can be used to determine which package and heat sink is a good candidate for design−in. The negative temperature coefficient trend of a CCR has a benefit as it helps to avoid thermal runaway. The following application examples will show how to determine which package device and the Cu needed for a simple circuit for the CCR device ONLY. The PD of the HB LED’s needs to be included for total circuit PD and total PCB area determination. Heat sinks attached to the PCB heat spreader are typically used to implement a total power solution. Figure 12. Circuit Design Example 2: For a series circuit with parallel CCR drivers (Figure 12), the power dissipation of each of the the CCRs is determined by: (Vsource – VLEDS ) x IREG. Using the worst case scenario; i.e, highest Vsource, Lowest LED VF, and highest target IREG. So, a 18 V source driving two white LEDs with a Vf of 3.5 V and 350 mA IREG would give: (18 V− (2 x 3.5 V)) x 0.350 A = 11 V x .35 A = 3.85 W for each CCR. By splitting the total power between 2 CCR’s, the thermal effect can be spread over a larger area and less concentrated. For an ambient temperature of 85°C, from the PD curves, each DPAK with 900 mm2, 2 oz Cu MCPCB would suffice. The negative temperature coefficient (NTC) of the CCR will actually lower the power dissipation by reducing the circuit current thus allowing a safety margin. Each LED will produce 3.5 V x 0.70 A = 2.45 W of additional power to thermally dissipate. Figure 11. Circuit Design Example 1: For a series circuit (Figure 11), the power dissipation of the CCR is determined by: (Vsource –VLEDS) x IREG. Using the worst case scenario; i.e, highest Vsource, Lowest LED VF, and highest target IREG. Thus, a 20 V source driving three white LEDs with a Vf of 3.5 V and 350 mA IREG would give: (20 V−(3x3.5 V)) x 0.350 A = 9.5 V x .35 A = 3.325 W. For an ambient temperature of 85°C, from the PD curves, a SMC with 2500 mm2, 2 oz Cu MCPCB would suffice. A DPAK with 900 mm2, 2 oz Cu MCPCB would also work. The negative temperature coefficient (NTC) of the CCR will actually lower the power dissipation by reducing the circuit current thus allowing a safety margin. Each LED will produce 3.5 V x 0.35 A = 1.23 W of additional power to be thermally dissipated. Figure 13. http://onsemi.com 12 AND9008/D Circuit Design Example 3: negative temperature coefficient (NTC) of the CCR will actually lower the power dissipation by reducing the circuit current thus allowing a safety margin. Each LED will produce 3.5 V x .136 A = 0.476 W of additional power to thermally dissipate. For a series circuit with parallel CCR drivers capable of adjusting the required current (Figure 13), the power dissipation of each of the the CCRs is determined by: (Vsource – VLEDS ) x IREG. Using the worst case scenario; i.e, highest Vsource, Lowest LED VF, and highest target IREG. So, a 18 V source driving two white LEDs with a Vf of 3.5 V and 350 mA IREG for the fixed current CCR would give: (18 V− (2 x 3.5 V )) x 0.350 A = 11 V x .35 A = 3.85 W. The adjustable CCR PD is (18 V− (2x3.5V )) x .150 A = 11 V x .15 A = 1.65 W. By splitting the total power between 2 CCR’s, the thermal effect can be spread over a larger area and less concentrated. For an ambient temperature of 85°C, from the PD curves, the fixed DPAK with 900 mm2, 2 oz Cu MCPCB would suffice while the adjustable DPAK would require only a 400 mm2, 2 oz Cu MCPCB. The negative temperature coefficient (NTC) of the CCR will actually lower the power dissipation by reducing the circuit current thus allowing a safety margin. Each LED will produce 3.5 V x .50 A = 1.75 W of additional power to thermally dissipate. + 10 to18 V 3.5 V 3.5 V NSI45090JDT4G Adjustable 90 to 160mA Figure 15. Circuit Design Example 5: For a series circuit with PWM dimming capability(Figure 15), the power dissipation of the CCRs is determined by analysis for worst case condition to account for 100% duty cycle. See Example 1. For analysis data. The method of pulsing the current through the LEDs is known as Pulse Width Modulation (PWM) and has become the preferred method of changing the light level. LEDs being a silicon device, turn on and off rapidly in response to the current through them being turned on and off. The switching time is in the order of 100 nanoseconds, this equates to a maximum frequency of 10 MHz. Applications will typically operate from a 100 Hz to 100 kHz. Below 100 Hz the human eye will detect a flicker from the light emitted from the LEDs. Between 500 Hz and 20 kHz the circuit may generate audible sound. Dimming is achieved by turning the LEDs on and off for a portion of a single cycle. This on off cycle is called the Duty cycle (D) and is expressed by the amount of time the LEDs are on (Ton) divided by the total time of a on/off cycle (Ts). Figure 14. Circuit Design Example 4: For a series circuit (Figure 14), the power dissipation of the CCR is determined by: (Vsource –VLEDS) x IREG. Using the worst case scenario; i.e, highest Vsource, Lowest LED VF, and highest target IREG. Thus, an 18 V source driving two white LEDs with a Vf of 3.5 V and 136 mA IREG would give: (20 V−(3x3.5 V)) x .136 A = 11 V x .136 A = 1.5 W. For an ambient temperature of 85°C, from the PD curves summary (Figure 10), the DPAK, with 400 mm2, 2 oz Cu MCPCB or a 700 mm2, 2 oz Cu FR4 PCB would suffice. The http://onsemi.com 13 AND9008/D in fine detail. Additionally, it was shown that an external bipolar junction transistor or bias resistor transistor can be used with a CCR for PWM to control the current and decrease power in the CCR. Summary The preceding Graphs and Tables show the size advantage of using MCPB versus standard FR4 material. It was presented that using MCPCB material can increase power dissipation by approximately 30% while decreasing board area by approximately 40%. This size tradeoff incurs a higher material costs; but, with size restrictions in LED lighting applications, this may become necessary. Figure 16. The data and examples presented in this application note and on the datasheets support the behavior described above APPENDIX A NSI45090JDT4G, Adjustable IREG = 90 −160 mA ±15% NSI50350ADT4G, Steady State IREG = 350 mA ±10% (Product Preview) SOD−123 Devices Are: NSI45015WT1G, Steady State IREG = 15 mA ±20% NSI45020T1G, Steady State IREG = 20 mA ±15% NSI45025T1G, Steady State IREG = 25 mA ±15% NSI45030T1G, Steady State IREG = 30 mA ±15% NSI45020AT1G, Steady State IREG = 20 mA ±10% NSI45025AT1G, Steady State IREG = 25 mA ±10% NSI45030AT1G, Steady State IREG = 30 mA ±10% NSI50010YT1G, Steady State IREG = 10 mA ±30% SMC Devices Are: NSI50350AST1G, Steady State IREG = 350 mA ±10% (Product Preview) SMB Devices Are: TBD, Vak max = 120 V, Steady State IREG = 50 mA ±10% (Product Preview) TBD, Vak max = 120 V, Steady State IREG = 30 mA ±10% (Product Preview) TBD, Vak max = 120 V, Steady State IREG = 20 mA ±15% (Product Preview) SOT−223 Devices Are: NSI45025ZT1G, Steady State IREG = 25 mA ±15% NSI45030ZT1G, Steady State IREG = 30 mA ±15% NSI45025AZT1G, Steady State IREG = 25 mA ±10% NSI45030AZT1G, Steady State IREG = 30 mA ±10% NSI45020JZT1G, Adjustable IREG = 20 −40 mA ±15% NSI45035JZT1G, Adjustable IREG = 35−70 mA ±15% SC−74 Devices Are: NSI45019JPT1G, Adjustable IREG = 19 −TBD mA ±15%, PWM enhanced (Product Preview) DPAK Devices Are: NSI45060JDT4G, Adjustable IREG = 60 −100 mA ±15% ON Semiconductor and are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). 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