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RT9241AGS Datasheet(PDF) 11 Page - Richtek Technology Corporation |
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RT9241AGS Datasheet(HTML) 11 Page - Richtek Technology Corporation |
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11 / 17 page  RT9241A/B 11 DS9241AB-05 March 2007 www.richtek.com Application Information RT9241A/B is a two-phase DC/DC controller that precisely regulates CPU core voltage and balances the current of different power channels. The converter consists of RT9241A/B and its companion MOSFET driver provide high quality CPU power and all protection function to meet the requirement of modern VRM. Voltage control The reference of VCORE is provided by a 5-bit DAC of VRM9.0 specification. Control loop consists of error amplifier, two-phase pulse width modulator, driver and power components. Like conventional voltage mode PWM controller, the output voltage is locked at the VREF of error amplifier and the error signal is used as the control signal VC of pulse width modulator. The PWM signals of different channels are generated by comparison of EA output and split-phase saw-tooth wave. Power stage transforms VIN to output by PWM signal on-time ratio. Current balance RT9241A/B senses the current of low side MOSFET in each synchronous rectifier when it is conducting for channel current balance and droop tuning. The differential sensing GM amplifier converts the voltage on the sense component (can be a sense resistor or the RDS(ON) of the low side MOSFET) to current signal into internal balance circuit. The current balance circuit sums and averages the current signals then produces the balancing signals injected to pulse width modulator. If the current of some power channel is greater than average, the balancing signal reduces the output pulse width to keep the balance. Load droop The sensed power channel current signals regulate the reference of DAC to form a output voltage droop proportional to the load current. The droop or so call “ctive voltage positioning” can reduce the output voltage ripple at load transient and the LC filter size. Fault detection The chip detects VCORE for over voltage and power good detection. The “hiccup mode” operation of over current protection is adopted to reduce the short circuit current. The in-rush current at the start up is suppressed by the soft start circuit through clamping the pulse width and output voltage. MOSFET driver detection and converter start up RT9241A/B interface with companion MOSFET driver (like RT9600 or HIP660X series) for correct converter initialization. The tri-phase PWM output (high, low, high impedance) pins sense the interface voltage at IC POR acts (both VDD and VDVD trip). The channel is enabled if the pin voltage is 1.2V less than VDD. Please tie the both PWM output to driver input for correct converter start- up. Current sensing setting RT9241A/B senses the current of low side MOSFET in each synchronous rectifier when it is conducting for channel current balance and droop tuning. The differential sensing GM amplifier converts the voltage on the sense component (can be a sense resistor or the RDS(ON) of the low side MOSFET) to current signal into internal circuit (see Figure 1). Figure 1. Current Sense Circuit Sample & Hold To Current Balance To Droop Tune To Over Current Detection 2/3 I X + - 2/3 I X 2/3 I X I X I BP I BN I L R S R SP R SN ISP X ISN X GM |
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