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ADP1823ACPZ-R7 数据表(PDF) 21 Page - Analog Devices |
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ADP1823ACPZ-R7 数据表(HTML) 21 Page - Analog Devices |
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21 / 32 page ![]() ADP1823 Rev. A | Page 21 of 32 Select RTOP between 1 kΩ and 10 kΩ. A good starting value is 2 kΩ. Next, calculate RBOT as FB OUT TOP FB BOT V V R V R − = (35) V 6 . 0 V 6 . 0 − × = OUT TOP BOT V R R (36) Note that if ratiometric tracking is used, substitute the actual FB voltage for the 0.6 V term used in Equation 36. Calculate the compensator gain needed at crossover to achieve 0 dB total system gain: COMP FILTER MOD T A A A A + + = (37) COMP FILTER MOD A A A + + = dB 0 (38) FILTER MOD COMP A A A − − = dB 0 (39) Calculate the value of RZ to achieve that gain: ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ × = TOP Z COMP R R A log 20 (40) ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ × = 20 10 COMP A TOP Z R R (41) Calculate the integrator cap value to place the compensation zero at the desired frequency: Z Z I f R π C 2 1 = (42) Calculate the capacitor value for the high frequency pole: P Z HF f R π C 2 1 = (43) Type III Compensator 0V VRAMP G (dB) PHASE –270° –90° fZ fP CHF CI RZ CFF RTOP RBOT FROM VOUT VREF EA COMP TO PWM RFF –1 SLO PE –1 SLO PE +1 SL OP E Figure 28. Type III Compensation 2 45 2 tan ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + φ = B K (44) and K f f CO Z = (45) and fP = fCO √K (46) Select RTOP between 1 kΩ and 10 kΩ. A good starting point is 2 kΩ. Next, calculate RBOT as FB OUT TOP FB BOT V V R V R − = (47) V 6 . 0 V 6 . 0 − × = OUT TOP BOT V R R (48) Note that if ratiometric tracking is used, substitute the actual FB voltage for the 0.6 V term in Equation 48. Calculate the feedforward capacitor to produce the first compensator zero: Z TOP FF f R π C 2 1 = (49) Calculate the resistor of the feedforward network to provide the first high frequency compensator pole: P FF FF f C π R 2 1 = (50) Calculate the impedance of the feedforward network at the crossover frequency, as this is required to set the gain of the compensator: FF CO FF FF R f C π Z + = 2 1 (51) Calculate the compensator gain needed at crossover to achieve 0 dB total system gain: AT = AMOD + AFILTER + ACOMP (52) 0 dB = AMOD + AFILTER + ACOMP (53) ACOMP = 0 dB − AMOD − AFILTER (54) Calculate the value of RZ to achieve that gain: ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ × = FF TOP Z COMP Z R R A || log 20 (55) () ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ × = 20 10 || COMP A FF TOP Z Z R R (56) Calculate the integrator cap value to place the compensation zero at the desired frequency: Z Z I f R π C 2 1 = (57) |
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