Rainbow-electronics MAX8720 Manual de usuario

General DescriptionThe MAX8720 step-down controller is intended for coreCPU DC-DC converters in notebook computers. It fea-tures a dynamically adjusta

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MAX8720Detailed DescriptionThe MAX8720 is a constant-on-time, quick-PWM con-troller with 6-bit VID inputs to dynamically set the outputvoltage from 0.

Free-Running, Constant-On-Time PWMController with Input Feed-ForwardThe quick-PWM control architecture is a pseudo-fixed-frequency, constant-on-time,

MAX8720On-times translate only roughly to switching frequen-cies. The on-times guaranteed in the ElectricalCharacteristics table are influenced by swi

dynamic output-voltage transitions when the inductorcurrent reverses at light or negative load currents. Withreversed inductor current, the inductor’s

MAX8720threshold between pulse-skipping PFM and nonskip-ping PWM operation to coincide with the boundarybetween continuous and discontinuous inductor-

Lot-to-lot variation of the threshold voltage can causeproblems in marginal designs. Typically, adding4700pF between DL and power ground (CNLin Figure

MAX8720Soft-Startup and Soft-Shutdown (SHDN)When SHDN goes low, the MAX8720 enters low-powershutdown mode. PGOOD goes low immediately. Theoutput volta

SMPS is active, initiating a transition to a new outputvoltage level. If this mode of DAC control is used, con-nect SUS low. Change D0–D5 together, av

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MAX8720When the CPU suspends operation (SUS = high), thecontroller overrides the 6-bit VID DAC code set byD0–D5, and slews the output voltage to the t

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Suspend Transition (Pulse-SkippingOperation Selected)If the MAX8720 is configured for pulse-skipping opera-tion (SKIP = GND) when SUS goes high, the M

MAX8720value also determines the load-current value atwhich PFM/PWM switchover occurs.Inductor SelectionThe switching frequency and inductor operating

low under a load transient. Ignoring the sag due tofinite capacitance:RESR≤ VSTEP/ ILOAD(MAX)The actual capacitance value required relates to thephysi

MAX8720significantly higher, consider increasing the size of NH.Conversely, if the losses at VIN(MAX)are significantlyhigher, consider reducing the si

where N is the number of high-side MOSFETs used forone regulator, and QGATEis the gate charge specifiedin the MOSFET’s data sheet. For example, assume

MAX8720PC Board Layout GuidelinesCareful PC board layout is critical to achieving lowswitching losses and clean, stable operation. Theswitching power

Layout Procedure1) Place the power components first, with ground ter-minals adjacent (NL source, CIN, COUT, and DLanode). If possible, make all these

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MAX8720Dynamically Adjustable 6-Bit VIDStep-Down ControllerMaxim cannot assume responsibility for use of any circuitry other than circuitry entirely e

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05151020251.995REFERENCE VOLTAGE DISTRIBUTIONMAX8720 toc18REFERENCE VOLTAGE (V)SAMPLE PERCENTAGE (%)1.998 2.0052.0022.000100µs/divSUSPEND TRANSITION(S