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BM6202FS-E2 Datasheet(PDF) 4 Page - Rohm |
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BM6202FS-E2 Datasheet(HTML) 4 Page - Rohm |
4 / 23 page 4/19 Datasheet Datasheet BM6202FS TSZ02201-0828AB400090-1-2 © 2013 ROHM Co., Ltd. All rights reserved. 22.FEB.2013 Rev.001 http://www.rohm.com TSZ22111 · 15 · 001 3) Bootstrap operation Figure 5. Charging period Figure 6. Discharging period The bootstrap is operated by the charge period and the discharge period being alternately repeated for bootstrap capacitor (CB) as shown in the figure above. In a word, this operation is repeated while the output of an external transistor is switching with synchronous rectification. Because the supply voltage of the floating driver is charged from the VCC power supply to CB through prevention of backflow diode DX, it is approximately (VCC-1V). The resistance series connection with DX has the impedance of approximately 200 Ω. The capacitance value for the bootstrap is the following formula: Example: Floating driver power supply quiescence current IBBQ : 150µA(max.) Bootstrap diode reverse bias current ILBD : 10µA(max.) Carrier frequency FPWM : 20kHz Output MOSFET total gate charge Qg : 25nC(max.) Floating driver transmission loss QLOSS : 1nC(max.) Drop voltage of the floating driver power supply dVDROP : 3V CBOOT » (( IBBQ + ILBD ) / FPWM + 2 x Qg + QLOSS ) / dVDROP ≈ 20nF The allowed drop voltage actually becomes smaller by the range of the used power supply voltage, the output MOSFET ON resistance, the forward voltages of the internal boot diode (the drop voltage to the capacitor by the charge current), and the power supply voltage monitor circuits etc. Please set the calculation value to the criterion about the capacitance value tenfold or more to secure the margin in consideration of temperature characteristics and the value change, etc. Moreover, the example of the mentioned above assumes the synchronous rectification switching. Because the total gate charge is needed only by the carrier frequency in the upper switching section, for example 150° commutation driving, it becomes a great capacity shortage in the above settings. Please set it after confirming actual application operation. 4) Thermal shutdown (TSD) circuit The TSD circuit operates when the junction temperature of the gate driver exceeds the preset temperature (150°C nominal). At this time, the controller forces all driver outputs low. Since thermal hysteresis is provided in the TSD circuit, the chip returns to normal operation when the junction temperature falls below the preset temperature (125°C nominal). The TSD circuit is designed only to shut the IC off to prevent thermal runaway. It is not designed to protect the IC or guarantee its operation in the presence of extreme heat. Do not continue using the IC after the TSD circuit is activated, and do not use the IC in an environment where activation of the circuit is assumed. Moreover, it is not possible to follow the output MOSFET junction temperature rising rapidly because it is a gate driver chip that monitors the temperature and it is likely not to function effectively. 5) Overcurrent protection (OCP) circuit The overcurrent protection circuit can be activated by connecting a low value resistor for current detection between the PGND pin and the GND pin. When the PGND pin voltage reaches or surpasses the threshold value (0.9V typical), the gate driver outputs low to the gate of all output MOSFETs, thus initiating the overcurrent protection operation. CB HO VS VDC VB L H DX LO OFF ON VCC CB HO VS VDC VB H L DX LO ON OFF VCC |
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