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FAN6751MRMY Fiches technique(PDF) 6 Page - Fairchild Semiconductor |
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FAN6751MRMY Fiches technique(HTML) 6 Page - Fairchild Semiconductor |
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6 / 13 page  AN-6073 APPLICATION NOTE © 2008 Fairchild Semiconductor Corporation www.fairchildsemi.com Rev. 1.0.0 • 9/26/08 6 If the conversion efficiency remains unchanged for a wide input voltage range, the maximum output power would be the same for a fixed IPK, which is limited by the internal current limiting threshold voltage VTH and RS. However, due to the time delay from the comparator to output stage inside the FAN6751, the maximum output power with high-line input is always higher than with low line. A 30% error is common for the universal input voltage range if the converter is operated in DCM. In CCM operation, the deviation becomes even larger. For the purpose of constant output power limit, the peak current limit VTH must be adjustable according to the VIN pin, which is proportional to input voltage. VIN=1V and VSENSE=0.83V at low line; VIN=3V and VSENSE=0.7 at high line. Figure 14. Universal Line Voltage Compensation for Constant Output Power Limit Protection Functions FAN6751 has protection functions in two categories: some enter Latch Mode and the others enter Recovery Mode. The Latch Mode can only be restart if VDD falls below 5V, as shown Figure 15. The Recovery Mode lets VDD decrease to UVLO mechanism until the fault condition removed, as shown Figure 16. Both modes prevent the SMPS from destructive states. Table 2 shows the relationship between protection functions and part numbers. Table 2. Protection Functions Protection Functions FAN6751MR FAN6751HL VDD Over-Voltage Protection (OVP) Recovery Latch Overload Protection (OLP) Recovery Latch Pull-High Protection Function by VIN > 4.7V Recovery Latch Internal Over Temperature Protection(OTP) Recovery Recovery SENSE Pin Short-Circuit Protection Recovery Recovery Brownout Protection Recovery Recovery VDD Over-Voltage Protection (OVP) VDD OVP has protection prevents damage due to over- voltage conditions. When the VDD voltage exceed 26V due to abnormal conditions, PWM output is turned off until the VDD voltage drops below UVLO then starts again (for MR) or Latched (for HL). OVP condition is usually caused by feedback open loops. Overload Protection (OLP) If the secondary output short circuits or the feedback loop is open, the FB pin voltage rises rapidly toward the open-loop voltage, VFB-OPEN. If the FB voltage remains above VFB-OLP and lasts for tD-OLP, the FAN6751 stops emitting output pulses and enters Recovery Mode (for FAN6751MR) or latched-up mode (for FAN6751HL), as shown in Figure 17. Power On Vds VDD 16.5V 7.5V 5V Normal operation Latch mode Without any switching OVP occurs Removed AC line Power On Remove Latch mode Normal operation 10.5V 26V Figure 15.VDD OVP Protection Waveforms for FAN6751HL, Latch Off Figure 16. VDD OVP Protection Waveforms for FAN6751MR, Recovery |
Numéro de pièce similaire - FAN6751MRMY |
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Description similaire - FAN6751MRMY |
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