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LM5181-Q1 Fiches technique(PDF) 11 Page - Texas Instruments |
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LM5181-Q1 Fiches technique(HTML) 11 Page - Texas Instruments |
11 / 33 page ˜ ˜ SET FB OUT D PS REF R R V V N V MAG PRI-PK(DCM) SW(DCM) DCM IN L I F D V ˜ ˜ OUT OUT D PRI-PK(DCM) MAG SW(DCM) 2 I V V I L F ˜ ˜ ˜ 2 MAG PRI-PK(DCM) OUT(DCM) SW(DCM) L I P F 2 ˜ ˜ OUT D OUT PRI-PK(BCM) IN 2 V V I I V D ˜ ˜ ˜ SW(BCM) MAG MAG PRI-PK(BCM) IN PS OUT D 1 F L L I V N V V § · ˜ ¨ ¸ ¨ ¸ ˜ © ¹ 2 MAG PRI-PK(BCM) OUT(BCM) SW(BCM) L I P F 2 ˜ ˜ ˜ ˜ OUT D PS IN OUT D PS V V N D V V V N 11 LM5181-Q1 www.ti.com SNVSBN6 – APRIL 2020 Product Folder Links: LM5181-Q1 Submit Documentation Feedback Copyright © 2020, Texas Instruments Incorporated Feature Description (continued) where • VD is the forward voltage drop of the flyback diode as its current approaches zero (1) The output power in BCM is given by Equation 2, where the applicable switching frequency and peak primary current in BCM are specified by Equation 3 and Equation 4, respectively. (2) (3) (4) As the load decreases, the LM5181-Q1 clamps the maximum switching frequency to 350 kHz, and the converter enters discontinuous conduction mode (DCM). The power delivered to the output in DCM is proportional to the peak primary current squared as given by Equation 5 and Equation 6. Thus, as the load decreases, the peak current reduces to maintain regulation at 350-kHz switching frequency. (5) (6) (7) At even lighter loads, the primary-side peak current set by the internal error amplifier decreases to a minimum level of 0.15 A, or 20% of its 0.75-A peak value, and the MOSFET off-time extends to maintain the output load requirement. The system operates in frequency foldback mode (FFM), and the switching frequency decreases as the load current is reduced. Other than a fault condition, the lowest frequency of operation of the LM5181-Q1 is 12 kHz, which sets a minimum load requirement of approximately 0.5% full load. 8.3.3 Setting the Output Voltage To minimize output voltage regulation error, the LM5181-Q1 senses the reflected secondary voltage when the secondary current reaches zero. The feedback (FB) resistor, which is connected between SW and FB as shown in Figure 17, is determined using Equation 8. where • RSET is nominally 12.1 kΩ (8) |
Numéro de pièce similaire - LM5181-Q1 |
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Description similaire - LM5181-Q1 |
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