データシートサーチシステム |
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LM22679 データシート(PDF) 10 Page - Texas Instruments |
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LM22679 データシート(HTML) 10 Page - Texas Instruments |
10 / 27 page 100 1k 10k 100k 1M 10M 0 5 10 15 20 25 30 35 40 FREQUENCY (Hz) -ADJ -5.0 LM22679, LM22679-Q1 SNVS581L – FEBRUARY 2013 – REVISED NOVEMBER 2014 www.ti.com Feature Description (continued) Figure 10. Compensator Gain In general, hand calculations or simulations can only aid in selecting good power stage components. Good design practice dictates that load and line transient testing should be done to verify the stability of the application. Also, Bode plot measurements should be made to determine stability margins. AN-1889 How to Measure the Loop Transfer Function of Power Supplies (SNVA364) shows how to perform a loop transfer function measurement with only an oscilloscope and function generator. 7.4 Device Functional Modes 7.4.1 Shutdown Mode The LM22679 device incorporates an input undervoltage lock-out (UVLO) feature. This prevents the regulator from turning on when the input voltage is not great enough to properly bias the internal circuitry. The rising threshold is 4.3 V (typ) while the falling threshold is 3.9 V (typ). 7.4.2 Active Mode The LM22679 is in Active Mode when VIN is above its UVLO level. See UVLO for more information on the UVLO level. 7.4.3 Current Limit The LM22679 device has current limiting to prevent the switch current from exceeding safe values during an accidental overload on the output. This peak current limit is found in the Electrical Characteristics table under the heading of ICL. The maximum load current that can be provided, before current limit is reached, is determined from Equation 4. (4) Where: L is the value of the power inductor. When the LM22679 enters current limit, the output voltage will drop and the peak inductor current will be fixed at ICL at the end of each cycle. The switching frequency will remain constant while the duty cycle drops. The load current will not remain constant, but will depend on the severity of the overload and the output voltage. For very severe overloads ("short-circuit"), the regulator changes to a low frequency current foldback mode of operation. The frequency foldback is about 1/5 of the nominal switching frequency. This will occur when the current limit trips before the minimum on-time has elapsed. This mode of operation is used to prevent inductor current "run-away", and is associated with very low output voltages when in overload. Equation 5 can be used to determine what level of output voltage will cause the part to change to low frequency current foldback. 10 Submit Documentation Feedback Copyright © 2013–2014, Texas Instruments Incorporated Product Folder Links: LM22679 LM22679-Q1 |
同様の部品番号 - LM22679_15 |
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同様の説明 - LM22679_15 |
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