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LTC3854EMSE 数据表(PDF) 10 Page - Linear Technology |
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LTC3854EMSE 数据表(HTML) 10 Page - Linear Technology |
10 / 28 page LTC3854 0 3854fa TheLTC3854canbeconfiguredtouseeitherDCR(inductor winding resistance) sensing or low value resistor sensing. The choice of the two current sensing schemes is largely a design tradeoff between cost, power consumption, and accuracy. DCR sensing is becoming popular because it eliminates expensive current sensing resistors and is more power efficient, especially in high current applica- tions.However,currentsensingresistorsprovidethemost accurate current limits for the controller. Other external component selection is driven by the load requirement, and begins with the selection of RSENSE (if RSENSE is used) andinductorvalue.Next,thepowerMOSFETsandSchottky diodesareselected.Finally,inputandoutputcapacitorsare selected. The Typical Application shown on the first page can be configured for operation up to 38V on VIN. SENSE+ and SENSE– Pins The SENSE+ and SENSE– pins are the inputs to the cur- rent comparator. The common mode input voltage range of the current comparator is 0V to 5.5V. Both SENSE pins are high impedance inputs with small input bias currents of less than 1μA. When the SENSE pins ramp up from 0V to 1.4V, small bias currents flow out of the SENSE pins. When the SENSE pins ramp down from 5.5V to 1.1V, the small bias currents flow into the SENSE pins. The high impedanceinputstothecurrentcomparatorallowaccurate DCR sensing. Using a Sense Resistor for Current Sensing A typical sensing circuit using a discrete resistor is shown in Figure 1. RSENSE is chosen based on the required output current. Thecurrentcomparatorhasamaximumthresholdof50mV. The input common mode range of the current comparator is 0V to 5.5V. The current comparator threshold sets the peak of the inductor current, yielding a maximum aver- age output current IMAX equal to the peak value less half the peak-to-peak ripple current, ∆IL. Allowing a margin of 20% for variations in the IC and external component values yields: RSENSE = 0.8 • VSENSE(MAX) IMAX + ∆IL 2 Inductor DCR Sensing For applications requiring the highest possible efficiency, the LTC3854 is capable of sensing the voltage drop across the inductor DCR, as shown in Figure 2. The DCR of the inductor represents the small amount of DC copper wind- ing resistance, which can be less than 1mΩ for today’s low value, high current inductors. When the external R1||R2•C1 time constant is chosen to be equal to the L/DCR time constant, the voltage drop across the external applicaTions inForMaTion Figure 1. Using a Resistor to Sense Current with the LTC3854 3854 F01 LTC3854 VIN INTVCC BOOST TG SW BG GND SENSE+ SENSE– VOUT RSENSE FILTER COMPONENTS PLACED NEAR SENSE PINS |
类似零件编号 - LTC3854EMSE |
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类似说明 - LTC3854EMSE |
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