AND8477/D P6P82PS01A: A “Drop-In” Active EMI Reduction IC For AC-DC and DC-DC Power Converters http://onsemi.com Prepared by: Kiran K. Kunduru ON Semiconductor APPLICATION NOTE Abstract Due to the concerns listed above, multiple EMI filters are used to reduce EMI over a broad range of frequencies (100 kHz − 400 kHz to 30 MHz) under which conducted emissions tests are performed. SS technology inherently offers better reduction at higher frequency harmonics and can serve as a single EMI solution over a broader range of frequencies. Moreover, there is no stability concern due to SS. However, to achieve optimal EMI reduction from SS ,an optimal combination of key SS parameters such as modulation rate, deviation, and modulation profile needs to be chosen for a given switching frequency. ON Semiconductor offers P6P82PS01A that can be used as a drop in companion IC on to a frequency−controlling node in a PWM converter. This device offers full flexibility to select the optimal modulation rate and deviation to achieve optimal EMI reduction. P6P82PS01A can either reduce or eliminate the input EMI filter and offer EMI reduction, with no impact on system stability. This application note focuses on P6P82PS01A versus Input EMI filters over a range of switching frequencies. PWM based converters are widely used in AC−DC, DC−DC power management applications. While PWM converters offer better efficiency and load/line regulation compared to linear regulators, PWM converters exhibit significant input EMI caused by the switching components. Input EMI filters are widely used to suppress and/or eliminate the EMI fed back to the input stage. Spread Spectrum (SS) technology, a method to dither the switching frequency over a wider frequency bandwidth is a powerful alternate EMI solution. ON Semiconductor introduces P6P82PS01A: A companion IC that can be dropped−in on to the frequency control node in a PWM controller, such as RT, or RT−CT nodes. This companion IC is targeted towards applications that employ AC−DC and DC−DC converters. Unlike EMI filters, P6P82PS01A offers better EMI reduction at the higher harmonics of the switching frequency. This application note compares EMI performance of EMI filters when compared to P6P82PS01A using Spread Spectrum technology. Introduction Switching in PWM converters causes input noise on both line and neutral nodes at the input stage. This noise manifests itself across the harmonics of the switching frequency. Regulatory agencies such as FCC and CISPR specify the compliance limits of this noise and the test procedures. The conducted emissions test specifications arise from the fact that these input noise harmonics cause unwanted electro−magnetic radiation when they traverse through a long cable (typically 1 m or longer). Bulk EMI filters at the input side are used to reduce this noise. There are two challenges in using EMI filters: 1. Any practical EMI filter is affected by unwanted parasitics. This degrades the filter performance and hence, a given EMI filter is effective only in a band of frequencies. 2. Adding EMI filters is a potential stability concern. Hence, some EMI filter configurations may not be feasible to realize. © Semiconductor Components Industries, LLC, 2010 December, 2010 − Rev. 0 P6P82PS01A IC : P6P82PS01A IC is targeted for RT/RT−CT based PWM controllers. P6P82PS01A is optimized for linear Modulation profile and provides the flexibility to control the deviation by varying the resistance at the SSEXTR pin (Pin 5). P6P82PS01A provides flexibility to control the modulation rate by : 1. Keeping MRSEL (Pin 7) pin low for internal Modulation rate control. 2. Keeping MRSEL (Pin 7) pin high for external Modulation rate control. 3. Internal modulation rate is controlled by varying a resistance at the MREXTR pin (Pin 2), when MRSEL (Pin 7) is low. 4. An external clock at the MREXTR pin (Pin 2) provides external modulation rate, when MRSEL (Pin 7) is high. 1 Publication Order Number: AND8477/D AND8477/D As shown in Figure 2, the RT/RT−CT pin of P6P82PS01A should connect to the RT/RT−CT pin of PWM controller. Figure 1. Pin Configuration of P6P82PS01A IC Figure 2. Application Schematic Circuit For P6P82PS01A Table 1. PIN DESCRIPTION Pin Pin Name Type 1 RT/RT−CT I/O 2 MREXTR I Description Input /Output pin connected to RT/RT−CT pin of PWM controller Selects Analog Modulation Rate through external resistor to GND when MRSEL pin pulled LOW. When MRSEL pin pulled HIGH, an external clock can be fed in to this pin. Has no default state. 3 NC 4 GND P Not connect Ground 5 SSEXTR I Analog Deviation selection through external resistor to GND. 6 NC 7 MRSEL I Modulation Rate Select. Selects Analog modulation clock when pulled LOW. Selects an External Modulation clock fed through MREXTR pin, when pulled HIGH. Has an internal pull−down resistor. 8 VDD P 3.3 V supply voltage. Not connect P6P82PS01A in an AC−DC Converter Application System Performance This case study is based on 3844 PWM controller with an RT−CT node to control PWM frequency. By changing RT, CT or both, PWM frequency can be varied. Capacitors C5, C6 are input EMI filters, shown in Figure 3. As shown in Figure 4, P6P82PS01A is added at the RT−CT node of PWM controller. Results from Table 2 show that system performance parameters like Ripple voltage, Mean output voltage and Efficiency are not impacted significantly with P6P82PS01A. Table 2. SYSTEM PERFORMANCE AT 50 kHz SWITCHING FREQUENCY Test Output Voltage (V) Ripple Voltage (mV) With EMI Filters With P6P82PS01A No EMI Filters 12.04 12.04 12.04 200 300 275 Efficiency at 0.5 A Load 37.04% 37.59% 37.59% Efficiency at 0.9 A Load 43.69% 44.55% 44.33% http://onsemi.com 2 AND8477/D EMI filters 3844 PWM controller Figure 3. AC to DC Converter Schematic Diagram AC−DC CONVERTER SYSTEM SETTINGS: P6P82PS01A added here. Switching frequency = 50 kHz. Input voltage 80−260 VAC. Output voltage−12 V. Figure 4. 3844 PWM Controller Schematic Diagram EMI PERFORMANCE Test settings: CE scan setting: CISPR−22, CLASS B standard in AVERAGE mode on LINE. P6P82PS01A device settings: MR = 12 kHz, %SPREAD = ±20. Figure 5. Original EMI http://onsemi.com 3 AND8477/D Figure 6. With Filters Figure 7. With P6P82PS01A Table 3. EMI REDUCTION TABLE Frequency (kHz) Original EMI (dBuV) With EMI Filters (dBuV) With P6P82PS01A (dBuV) Reduction With EMI Filters (dBuV) Reduction With P6P82PS01A (dBuV) 150 64 66 56 −2 8 200 66 68 59 −2 7 250 65 63 56 2 9 300 63 59 58 4 5 350 64 58 57 6 7 400 64 55 56 9 8 450 61 50 53 11 8 500 59 45 52 14 7 1000 51 44 44 7 7 2000 50 43 40 7 10 4000 48 42 40 6 8 5000 48 43 41 5 7 9000 47 45 39 2 8 10000 47 46 39 1 8 15000 45 50 38 −5 7 20000 32 45 28 −13 4 30000 15 35 15 −20 0 http://onsemi.com 4 AND8477/D Results from Table 3, Figures 5, 6 and 7, show that P6P82PS01A gives better EMI reduction compared to EMI filters. As shown in Figure 8, capacitor C1, C12, C13, C14 are input EMI filters and P6P82PS01A is added at the RT node of PWM controller. P6P82PS01A IN an DC−DC CONVERTER application: System Performance This case study is based on TPS54317, a 1.6 MHz, 3 V to 6 V input, 3 A synchronous step−down swift converter. It has an Adjustable output voltage from 0.9 V to 2.5 V. Operating frequency range is 280 kHz to 1.6 MHz, controlled by the timing resistor (RT) (R4 in Figure 8). Results from Tables 4 and 5, show that system performance parameters like Ripple voltage, Mean output voltage, and Efficiency are not impacted significantly with P6P82PS01A at 280 kHz and 1 MHz PWM frequencies. EMI filters P6P82PS01A added here Figure 8. TPS54317–EVM Schematic Diagram Table 4. SYSTEM PERFORMANCE AT 1 MHz Test With EMI Filters With P6P82PS01A No EMI Filters 2.428 2.427 2.426 290 296 270 Efficiency at Load of 0.5 A 91.74% 91.66% 91.66% Efficiency at Load of 1.5 A 87.15% 86.47% 86.5% Test With EMI Filters With P6P82PS01A No EMI Filters Output Voltage (V) 2.427 2.426 2.426 Ripple Voltage (mV) 530 640 550 Efficiency at Load of 0.5 A 89.69 91.82% 89.54% Efficiency at Load of 1.5 A 87.34% 87.96% 87.96% Output Voltage (V) Ripple Voltage (mV) Table 5. SYSTEM PERFORMANCE AT 280 kHz http://onsemi.com 5 AND8477/D EMI Performance Test settings: CE scan setting: CISPR−22, CLASS B standard in AVERAGE mode on LINE. P6P82PS01A device settings: MR = 25 kHz, %SPREAD = ±20. Figure 9. Original EMI AT 280 kHz PWM Frequency Figure 10. With Filters at 280 kHz PWM Frequency Figure 11. With P6P82PS01A at 280 kHz PWM Frequency http://onsemi.com 6 AND8477/D Table 6. EMI REDUCTION TABLE AT 280 kHz Frequency (kHz) Original EMI (dBuV) With EMI Filters (dBuV) With P6P82PS01A (dBuV) Reduction With EMI Filters (dBuV) Reduction With P6P82PS01A (dBuV) 280 86 72 82 14 4 560 55 52 48 3 7 840 62 59 53 3 9 1120 59 64 48 −5 11 1400 49 58 47 −9 2 1680 35 42 38 −7 −3 1960 42 59 36 −17 6 2240 39 60 30 −21 9 2520 30 52 26 −22 4 2800 25 41 24 −16 1 3080 36 47 25 −11 11 5040 35 20 28 15 7 10080 36 30 30 6 6 15120 35 30 28 5 7 20160 28 24 27 4 1 29960 27 22 27 5 0 Results from the Table 6, Figures 9, 10 and 11, show that P6P82PS01A gives better EMI reduction compared to EMI filters. Figure 12. Original EMI AT 1 MHz PWM Frequency http://onsemi.com 7 AND8477/D Figure 13. With Filters at 1 MHz PWM Frequency Figure 14. With P6P82PS01A at 1 MHz PWM Frequency Table 7. EMI REDUCTION TABLE AT 1 MHz Frequency (MHz) Original EMI (dBuV) With EMI Filters (dBuV) With P6P82PS01A (dBuV) Reduction With EMI Filters (dBuV) Reduction With P6P82PS01A (dBuV) 1 63 66 2 32 52 57 −3 6 26 −20 6 3 32 51 23 −19 9 4 38 44 23 −6 15 5 37 28 26 9 11 6 37 21 24 16 13 7 38 32 24 6 14 8 35 34 24 1 11 9 35 24 24 11 11 10 35 32 24 3 11 15 35 37 26 −2 9 20 32 25 24 7 8 30 25 22 19 3 6 Results from Table 7, Figures 12, 13 and 14, show that P6P82PS01A gives better reduction compared to filters. http://onsemi.com 8 AND8477/D In this application note, the deviation setting was ±20% in all case studies. However, P6P82PS01A provides flexibility to control the deviation other than ±20% to suit EMI performance and system performance requirements. Given its flexibility in controlling the key SS parameters, P6P82PS01A is the ideal EMI solution to pass conducted EMI compliance tests and can be used to reduce, if not eliminate, EMI filters. Summary At three different PWM frequencies in both DC−DC as well as AC−DC converters, it can be observed that P6P82PS01A can be used as an effective active EMI reduction solution. In all the cases, especially at the higher harmonics, the performance of P6P82PS01A is superior to EMI filters (input EMI filters for DC−DC and common mode EMI filters for AC−DC converters). Moreover, P6P82PS01A also reduces the BOM and saves PCB space (2 mm x 2 mm package vs. bulk capacitances and inductances). ON Semiconductor and are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC reserves the right to make changes without further notice to any products herein. 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