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RT9237CS Datasheet(PDF) 11 Page - List of Unclassifed Manufacturers |
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RT9237CS Datasheet(HTML) 11 Page - List of Unclassifed Manufacturers |
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11 / 15 page  Preliminary RT9237 DS9237-00 January 2002 www.richtek-ic.com.tw 11 IMP RAMP R k 56 V 1 V Ω × = kHz 2 . 1 LC 2 1 = π kHz 8 . 8 CR 2 1 ESR = π 1 2 Z C R 2 1 F π = ) C C C C ( R 2 1 F 2 1 2 1 2 P + × π = Design Example Three phase converter VCORE = 1.5V, VIN = 12V, full load current = 60Amp, droop voltage at full load = 120mV, OCP trip point for each power stage = 30Amp (at Sample/Hold), low side MOSFET RDS(ON) = 6m Ω at room temperature, L = 2µH, COUT = 9000 µF, capacitor ESR = 2m Ω. 1. Compensation setting a. Modulator Gain, Pole and Zero Modulator Gain = , saw-tooth wave amplitude , choose RIRMP = 39K, VRAMP = 1.4V, modulator Gain = 8.6 = 18.7dB, LC filter pole = , ESR zero = b. EA compensation network Use type 2 compensation scheme (see Fig. 5), , , mid-band gain = . Choose R1 = 2.4K Ω, R2 = 24K Ω, C1 = 6.6nF, C2 = 33pF, get FZ = 1KHz, Fp = 200KHz, mid-band Gain=10=20dB, modulator asymptotic Bode plot of EA compensation and PWM loop Gain Bode shown as Fig. 6. Fig. 5 EA Compensation Network Fig. 6 Asymptotic Bode Plot of PWM Loop Gain 2. Droop setting Full load current of each power channel = 60A/3 = 20Amp, the ripple current = ∆IL = , load current at S/H = , GM Amp S/H , suggested IX at full = 40 µA〜50µA, choose RSP = RSN = 2.7KΩ, IX(MAX) = 40.8 µA, required Droop = 120mV = 40.8 µA×3×2/3×RADJ ，RADJ = 1.47KΩ. Take the temperature rising for consideration, if MOSFET working temperature=70 °C and the temperature coefficient =5000ppm/ °C, the RDS(ON)(70 °C) = 6mΩ × {1+(70°C-27°C) × 5000ppm/ °C} = 7.3 mΩ, RADJ(70°C) = RADJ(27°C) × {RDS(ON)(27°C)/RDS(ON)(70°C)} = 1.21KΩ 3. Over Current Protection setting OCP trip point current = 30A (at Sample/Hold)， ， RIMAX=13.6K Ω Take the temperature rising for consideration, RIMAX(70 °C) = RIMAX(27°C) × {RDS(ON)(27 °C)/RDS(ON)(70°C)} = 11.2KΩ 4. SS capacitor CSS = 0.1 µF is the suitable value for most application. RAMP IN V V 1 2 R R Asymptotic Bode Plot of PWM Loop Gain -60 -40 -20 0 20 40 60 80 100 10 100 1000 10000 100000 1000000 10000000 Frequency (Hz) 10 100 1K 10K 100K 1M 10M Uncompensated EA Gain Compensated EA Gain Modulator Gain PWM Loop Gain A 28 . 3 V 12 V 5 . 1 1 H 2 V 5 . 1 S 5 = − × µ × µ A 36 . 18 2 I A 20 L = ∆ − SP ) ON ( DS ) MAX ( X R A 36 . 18 R I × = IMAX SP ) ON ( DS X R V 6 . 0 2 3 R A 30 R I × = × = _ EA C1 C3 C2 R2 R3 R1 FB DACOUT VCORE COMP R3, C3 are used in type 3 compensation scheme (left NC in type 2) ROL ROL for no load offset setting |
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