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LM2576T-5.0 データシート(PDF) 20 Page - National Semiconductor (TI) |
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LM2576T-5.0 データシート(HTML) 20 Page - National Semiconductor (TI) |
20 / 24 page Definition of Terms (Continued) CAPACITOR EQUIVALENT SERIES RESISTANCE (ESR) The purely resistive component of a real capacitor’s imped- ance (see Figure 16). It causes power loss resulting in capacitor heating, which directly affects the capacitor’s op- erating lifetime. When used as a switching regulator output filter, higher ESR values result in higher output ripple volt- ages. Most standard aluminum electrolytic capacitors in the 100 µF–1000 µF range have 0.5 Ω to 0.1Ω ESR. Higher- grade capacitors (“low-ESR”, “high-frequency”, or “low- inductance”) in the 100 µF–1000 µF range generally have ESR of less than 0.15 Ω. EQUIVALENT SERIES INDUCTANCE (ESL) The pure inductance component of a capacitor (see Figure 16). The amount of inductance is determined to a large extent on the capacitor’s construction. In a buck regulator, this unwanted inductance causes voltage spikes to appear on the output. OUTPUT RIPPLE VOLTAGE The AC component of the switching regulator’s output volt- age. It is usually dominated by the output capacitor’s ESR multiplied by the inductor’s ripple current ( ∆I IND). The peak- to-peak value of this sawtooth ripple current can be deter- mined by reading the Inductor Ripple Current section of the Application hints. CAPACITOR RIPPLE CURRENT RMS value of the maximum allowable alternating current at which a capacitor can be operated continuously at a speci- fied temperature. STANDBY QUIESCENT CURRENT (I STBY) Supply current required by the LM2576 when in the standby mode (ON /OFF pin is driven to TTL-high voltage, thus turning the output switch OFF). INDUCTOR RIPPLE CURRENT ( ∆I IND) The peak-to-peak value of the inductor current waveform, typically a sawtooth waveform when the regulator is operat- ing in the continuous mode (vs. discontinuous mode). CONTINUOUS/DISCONTINUOUS MODE OPERATION Relates to the inductor current. In the continuous mode, the inductor current is always flowing and never drops to zero, vs. the discontinuous mode, where the inductor current drops to zero for a period of time in the normal switching cycle. INDUCTOR SATURATION The condition which exists when an inductor cannot hold any more magnetic flux. When an inductor saturates, the induc- tor appears less inductive and the resistive component domi- nates. Inductor current is then limited only by the DC resis- tance of the wire and the available source current. OPERATING VOLT MICROSECOND CONSTANT (E •T op) The product (in VoIt •µs) of the voltage applied to the inductor and the time the voltage is applied. This E •T op constant is a measure of the energy handling capability of an inductor and is dependent upon the type of core, the core area, the number of turns, and the duty cycle. Connection Diagrams (Note 15) Straight Leads 5-Lead TO-220 (T) Top View 01147621 LM2576T-XX or LM2576HVT-XX NS Package Number T05A TO-263 (S) 5-Lead Surface-Mount Package Top View 01147625 LM2576S-XX or LM2576HVS-XX NS Package Number TS5B LM2576SX-XX or LM2576HVSX-XX NS Package Number TS5B, Tape and Reel Bent, Staggered Leads 5-Lead TO-220 (T) Top View 01147622 LM2576T-XX Flow LB03 or LM2576HVT-XX Flow LB03 NS Package Number T05D Note 15: (XX indicates output voltage option. See ordering information table for complete part number.) 01147620 FIGURE 16. Simple Model of a Real Capacitor www.national.com 20 |
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同様の説明 - LM2576T-5.0 |
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