POWER MANAGEMENT CIRCUITS

What is power management?

Domains of power management

TYPICAL APPLICATIONS

WORLD WIDE POWER MANAGEMENT

DC - DC CONVERSION

• Low Drop-Out Regulators(LDO).

• Inductor based switched mode power converter.

• Switched capacitor converters.

LDO

Idea is to control the R1Use feedback control to adjust value of R1

Model of a LDO

Simple and low noise

Output is lower than inputHigh efficiency only if Vo is closer to Vg.

Linear regulator efficiency cannot be greater than ratio of output voltage to input voltage

BUCK CONVERTER: STEP DOWN SWITCHING CONVERTER

Conversion ratio of BUCK Conveter: D=

(Vo/Vg)

Step down conversion

BOOST CONVERTER

Conversion ratio of boost converter

Thus it’s a step up conversion.

BUCK BOOST CONVERTER

Voltage Conversion ratio

SWITCH CAPACITOR CIRCUITS

MOTIVATONS

Inductor-less On-chip integration Low cost High switching frequency Easy to implement (open-loop system) Fast transient but large ripple High efficiency but limited output power

SWITCHED CAPACITOR CIRCUITS

On-chip scalable voltage generation Good choice for very low power battery operated system Voltage scaling below 1V

COMPARISON

POWER SUPPLY DESIGN: HELPFUL HINTSEfficiency not an issue? Linear regulators may be best.Battery powered? Consider switcher for efficiency.Vout > Vin? Use a switcher (Boost). With switchers, stick to simple topologies like Boost and Buck. Advanced topologies not for the faint of heart! Use a combination of switchers and linear regulators to get multiple output voltages.Electrical noise an issue (e.g., with A/D converters)?Need to double (2 x Vin) or invert (-Vin)? Consider a capacitive ‘charge pump’ . Put batteries in series, not parallel. Parallel batteries can rapidly self-discharge, wasting battery life.

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