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BD8153EFV Datasheet(PDF) 9 Page - Rohm |
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BD8153EFV Datasheet(HTML) 9 Page - Rohm |
9 / 18 page BD8153EFV Technical Note 9/17 www.rohm.com 2009.07 - Rev.B © 2009 ROHM Co., Ltd. All rights reserved. (4) Setting RC, CC of the Phase Compensation Circuit In the current mode control, since the coil current is controlled, a pole (phase lag) made by the CR filter composed of the output capacitor and load resistor will be created in the low frequency range, and a zero (phase lead) by the output capacitor and ESR of capacitor will be created in the high frequency range. In this case, to cancel the pole of the power amplifier, it is easy to compensate by adding the zero point with CC and RC to the output from the error amp as shown in the illustration. Open loop gain characteristics Pole at the power amplification stage When the output current reduces, the load resistance Ro increases and the pole frequency lowers. Error amp phase compensation characteristics Zero at the power amplification stage When the output capacitor is set larger, the pole frequency lowers but the zero frequency will not change. (This is because the capacitor ESR becomes 1/2 when the capacitor becomes 2 times.) It is possible to realize the stable feedback loop by canceling the pole fp(Min.), which is created by the output capacitor and load resistor, with CR zero compensation of the error amp as shown below. fz(Amp.) = fp(Min.) 1 = 1 2 Rc Cc 2 Romax Co 1 Fp = 2 RO CO 1 fz(ESR) = 2 ESR CO 1 fp(Min) = 2 ROMax CO [Hz] at light load 1 fz(Max) = 2 ROMin CO [Hz] at heavy load 1 fp(Amp.) = 2 Rc Cc fp(Min) fp(Max) fz(ESR) A 0 -90 0 Gain [dB] Phase [deg] lOUTMin lOUTMax 0 0 A -90 Gain [dB] Phase [deg] L VCC Rc Cc Cin Vcc,PVcc GND,PGND SW COMP Co ESR Ro Vo Fig. 29 Gain vs Phase Fig. 30 Application Circuit Diagram [Hz] [Hz] [Hz] [Hz] |
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