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MLX90285LVKABA-000BU Datasheet(PDF) 6 Page - Melexis Microelectronic Systems |
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MLX90285LVKABA-000BU Datasheet(HTML) 6 Page - Melexis Microelectronic Systems |
6 / 13 page MLX90285 24V Low Noise Two-Coil Fan Driver 3901090285 Rev. 005 Page 6 of 14 DataSheet Aug/14 B 10 Unique Features 10.1 Active Soft Switching The use of the Melexis Soft Switching techniques in the US168/169 and US651/661 has already proven its efficiency to noticeably reduce electrical and acoustic noise by precisely control the output slope duration on the fan coil. The US168/168 is the first generation with fixed output slope duration and the US651/661 is the second generation with possibility for the user to fine-tune the slope duration via an external pin. The MLX90285 represents the third generation of soft switching device as it goes even a step further into intelligence and smart driving. It mainly combines the major advantage of each previous generation: Adjustable Slope Control best balance between motor performance and acoustic/electrical noise No need of external component for slope control cost efficiency and simplicity “Adjustable without external component” is possible as the device automatically determine the slope duration depending on the fan rotation speed. The MLX90285 determines the fan rotation speed by measuring the half output switching period from the magnetic field signal. The output slope duration is extrapolated by measuring the duration from the falling edge on OUT1 to the cross over with OUT2. The result is processed to determine the actual Output Slope Duration to Torque Period Ratio (SLRATIO = 2 . tSLOPE / TOUT ), leading to two possible options: If SLRATIO < 6.25% (typical), the slope duration should be increased If SLRATIO > 6.25% (typical), the slope duration should be decreased The Digital Slope Duration Control register is incremented or decremented accordingly, thus updating the slope duration value for both outputs OUT1 and OUT2, prior the next rising slope occurring on OUT1. Magnetic Field at Hall sensor B OP (from rotor magnet) RP Digital Magnetic Field (North or South) ½ . T OUT1 = ½ . 7.5ms = 3.75ms V OUT1 V OUT2 Output Voltage Output crossover OUT1 slope duration measurement signal ½ t SLOPE = 0.15ms ½ t SLOPE = 0.145ms Slope Duration to Output Switching Period Ratio register Digital Slope Duration Control register ( 1 N 96 ) SL RATIO comparison + decision = 0.3ms / 3.75ms = 8% Slope duration must be decreased N = N 0 (= 53) t SLOPE = REF . N (= REF . 53 = 0.3ms) t SLOPE = REF . (N0 - 1) (= REF . 52 = 0.29) 1 - All values in green are arbitrary and just given for example purpose 2 - Condition example: 4000RPM, 2-pole pair rotor magnet, initial slope duration = 0.3ms, target SL RATIO = 6.25% Picture 1 – Active Soft Switching Operation Principle |
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