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BD7679G Datasheet(PDF) 7 Page - Rohm |
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BD7679G Datasheet(HTML) 7 Page - Rohm |
7 / 20 page 7/17 Datasheet Datasheet BD7679G TSZ02201-0F2F0A200160-1-2 © 2015 ROHM Co., Ltd. All rights reserved. 2015.6.24 Rev.002 www.rohm.com TSZ22111・15・001 ( 4 ) Over Current Limiter and Leading Edge Blanking Period BD7679G has over current limiter for each switching cycle. When the CS pin voltage exceeds the VCS voltage (=0.5V Typ), switching is turned OFF. In addition, when the driver MOSFET is turned ON, surge current occurs at each capacitor component and drive current. Therefore, when the CS pin voltage rises temporarily, the detection errors may occur in the over current limiter circuit. To prevent detection errors, the OUT pin is switched from low to high and the CS signal is blanked for 250nsec by the LEB (Leading Edge Blanking) function. This blanking function enables a reduction of CS pin noise filtering in response to noise that occurs when the OUT pin is switched from low to high. ( 5 ) Output Overload Protection Function (FB OLP Comparator ) Overload Protection Function monitors the load status of secondary output through FB pin and stops the switching of OUT pin during excessive load. In over load condition, there is no current in photo-coupler because output voltage decreases (drops) while FB pin voltage rises. When FB pin voltage exceeds VFOLP1A (=3.6V Typ) at TFOLP (=250ms Typ) interval continuously, a load is excessive and OUT pin is fixed to L. The timer of overload protection is reset when FB pin drops further than VFOLP1B (=3.4V Typ) within TFOLP (=250ms Typ) after exceeding VFOLP1A (=3.6V Typ). Switching functions within this TFOLP (=250ms Typ). FB voltage, which is pulled up in resistance to IC internal voltage operates from VFOLP1A (=3.6V Typ) or more at start-up. For this matter, set the start-up time of the secondary output voltage such that the FB voltage is always VFOLP1B (=3.4V Typ) or less within TFOLP (=250ms Typ) at start-up. Figure 9, Overload Protection (Self-restart) ( 6 ) COMP Pin External Stop Function IC is stopped when the COMP pin voltage rises to VSTOP1 (2.0V Typ). A masking timer for TSTOP (=100us Typ) prepared to prevent operation errors caused by noise. Once IC stops by COMP stop function, IC stops until COMP < VSTOP2(=1.8V.Typ). Overheating Protection by Posistor When a posistor is attached to the COMP pin shown Figure-10, the switching operation can be stopped when overheating occurs. Figure 10 COMP Pin Overheating Protection Application |
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