Datenblatt-Suchmaschine für elektronische Bauteile |
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LM3151 Datenblatt(PDF) 10 Page - Texas Instruments |
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LM3151 Datenblatt(HTML) 10 Page - Texas Instruments |
10 / 26 page ICL IPK 'I IOCL IOUT Load Current Increases Normal Operation Current Limited 'I = (VIN - VOUT) x tON L Ivalley = IOUT - ' IL 2 VCL (Tj) = VCL x [1 + 3.3 x 10 -3 x (Tj - 27)] ICL (Tj) = VCL (Tj) RDS(ON)max LM3151, LM3152, LM3153 SNVS562G – SEPTEMBER 2008 – REVISED MARCH 2011 www.ti.com Current Limit Current limit detection occurs during the off-time by monitoring the current through the low-side switch. If during the off-time the current in the low-side switch exceeds the user defined current limit value, the next on-time cycle is immediately terminated. Current sensing is achieved by comparing the voltage across the low-side switch against an internal reference value, VCL, of 200 mV. If the voltage across the low-side switch exceeds 200 mV, the current limit comparator will trigger logic to terminate the next on-time cycle. The current limit ICL, can be determined as follows: where • IOCL is the user-defined average output current limit value • RDS(ON)max is the resistance value of the low-side FET at the expected maximum FET junction temperature • VCL is the internal current limit reference voltage • Tj is the junction temperature of the LM3151/2/3 Figure 12 illustrates the inductor current waveform. During normal operation, the output current ripple is dictated by the switching of the FETs. The current through the low-side switch, Ivalley, is sampled at the end of each switching cycle and compared to the current limit threshold voltage, VCL. The valley current can be calculated as follows: where • IOUT is the average output current • ΔIL is the peak-to-peak inductor ripple current If an overload condition occurs, the current through the low-side switch will increase which will cause the current limit comparator to trigger the logic to skip the next on-time cycle. The IC will then try to recover by checking the valley current during each off-time. If the valley current is greater than or equal to ICL, then the IC will keep the low-side FET on and allow the inductor current to further decay. Throughout the whole process, regardless of the load current, the on-time of the controller will stay constant and thereby the positive ripple current slope will remain constant. During each on-time the current ramps up an amount equal to: The valley current limit feature prevents current runaway conditions due to propagation delays or inductor saturation since the inductor current is forced to decay following any overload conditions. Figure 12. Inductor Current - Current Limit Operation 10 Submit Documentation Feedback Copyright © 2008–2011, Texas Instruments Incorporated Product Folder Links: LM3151 LM3152 LM3153 |
Ähnliche Teilenummer - LM3151_15 |
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Ähnliche Beschreibung - LM3151_15 |
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