Rainbow-electronics MAX8775 Manual de usuario

General DescriptionThe MAX8775 is a dual, step-down, interleaved, fixed-frequency, switch-mode power-supply (SMPS) con-troller with synchronous rectif

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MAX8775Detailed DescriptionThe MAX8775 is a dual fixed-frequency step-down con-troller for low-voltage I/O and graphics core (GPU) sup-plies. It can b

output voltages required by the different GPU operatingand sleep states. Automatic fault blanking, forced-PWMoperation, and transition control are ach

MAX8775current balance. PGOOD1 indicates when the com-bined output is in regulation, while PGOOD2 indicatesthe currents in both phases are balanced. P

See Table 1 for component selections and Table 2 forthe component manufacturers.SMPS 5V Bias Supply (VCCand VDD)The MAX8775 SMPSs require a 5V bias su

MAX8775SMPS Detailed DescriptionSMPS Enable Controls (ON1, ON2)ON1 and ON2 provide independent control of outputsoft-start and soft-shutdown. This all

without a traditional error amplifier and the phase shiftassociated with it.The MAX8775 uses a relatively low loop gain, allowingthe use of lower cost

MAX8775When selecting a switching frequency, the minimum on-time at the highest input voltage and lowest output voltagemust be greater than the 150ns

In combined-mode operation, since the load is sharedbetween two phases, the load current at whichPFM/PWM crossover occurs is twice that of eachphase’s

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MAX8775Setting DTRANS high disables the forced downwardREFIN_ transition. This allows the output voltage to driftdown at a rate determined by the load

While ON2 is low, PGOOD2 is blanked high imped-ance. When ON2 goes high again, the PGOOD2 cur-rent-balance comparator is reenabled.Current Balance (CC

MAX8775In combined mode (REFIN2 = VCC), PGOOD1 indi-cates the output voltage is in regulation, while PGOOD2indicates the currents between the two phas

Thermal-Fault ProtectionThe MAX8775 features a thermal-fault protection circuit.When the junction temperature rises above +160°C, athermal sensor sets

MAX8775mode. The amount of overshoot during a full-load to no-load transient due to stored inductor energy can be cal-culated as:where NPHis 2 in comb

and:where RCSis the required current-sense resistance,and RDCRis the inductor’s series DC resistance. Usethe worst-case inductance and RDCRvalues prov

MAX8775where IINis the average input current:In combined mode (REFIN2 = VCC) with both phasesactive, the input RMS current simplifies to:For most appl

where ILIMITis the peak current allowed by the current-limit circuit, including threshold tolerance and sense-resistance variation. The MOSFETs must h

MAX8775where a single mΩ of excess trace resistance caus-es a measurable efficiency penalty.• Minimize current-sensing errors by connectingCSH_ and CS

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MAX8775Dual and Combinable Graphics CoreController for Notebook ComputersMaxim cannot assume responsibility for use of any circuitry other than circui

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