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BD9739KN Datasheet(PDF) 9 Page - Rohm |
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BD9739KN Datasheet(HTML) 9 Page - Rohm |
9 / 15 page Technical Note 9/14 www.rohm.com 2010.09 - Rev.A © 2010 ROHM Co., Ltd. All rights reserved. BD9739KN,BD9740KN 10. Setting MAX DUTY The DTC voltage is determined by the internal R1 and R2 resistance values. The DTC voltage can be changed by connecting resistance values that are from 1 to 2 digits smaller than the internal R1 (30 k ) and R2 (93 k) resistors, to the RA and RB pins. *The resistors connected to the RA and RB pins should be at least 5 k . Avoid shorting the VREGA and DTC pins. *When VCC falls to 2.8 V or below, a protection circuit will operate to limit MAX DUTY in order to prevent the IC from malfunctioning when VREGA (the internal circuit power supply) drops. 11. Soft start operation triggered by the DTC pin Soft start operation can be set by connecting a capacitor to the DTC pin. Setting the STBY pin to high will cause the capacitor connected to the DTC pin to be charged by the internal pull-up resistor. Startup will begin when this voltage reaches the minimum voltage of the CT pin's triangular waveform. *Set the capacitance connected to each DTC pin to 10 μF or less. 12. Internal soft start operation Soft start times are set internally for CH4, CH6, and CH7 (BD9739KN); and CH2 to CH4 (BD9740KN). BD9739KN CH4, 6, 7: 2.7 ms BD9740KN CH2 to CH4: 3.6 ms (Soft start operation of CH2 and CH3 is delayed until CH4 reaches approximately 80%.) 13. Setting the error amp feedback resistance (1) Feedback resistance order (BD9739KN, BD9740KN) Error amp differential input is formed by a PNP transistor, with the base current of this input flowing into the lower voltage divider resistor. In the worst case, this current may reach 0.2 μA. For this reason, when the resistance of the lower resistor is increased, the base current may cause an error in the output voltage. For example, resistance values of 40 k , 20 k, and 10 k result in errors of 1%, 0.5%, and 0.25%, respectively. Refer to these values when setting the resistance value. (2) Setting the inverted channel (BD9739KN, BD9740KN) For the BD9739KN, connect the CH5 error amp reference voltage (INV5) to the ground. For the BD9740KN, the CH6 error amp reference voltage is grounded internally. *It is recommended to use a 10 k resistor between VREF and CH5 output. Use a resistance value from 5 k to 20 k. |
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