LTC3106 datasheet(21/38 Pages) LINER

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LTC3106

3106f

For more information www.linear.com/LTC3106

BOOST MODE

BUCK-BOOST MODE

BUCK MODE

VOUT

IMAX

IPEAK

IVALLEY

IZERO

VIN

tOFF

3106 F06

VIN

VOUT

SW1

SW2

Figure 6. Operating Voltage and Current Waveforms

operaTion

Normal Operation

When VAUX is in regulation (~5.2V) and VOUT is greater

than1.2Vtypical,theconverterwillenternormaloperation.

AlwaysprioritizingVINoverVCAP,theintegratedPowerPath

controlcircuitryprovidesseamlesstransitionbetweeninput

sources as needed to maintain regulation of the output

voltage and to periodically recharge VAUX.

Anaccuratecomparatorisusedtomonitortheoutputvolt-

age as it continues to charge to one of the user selected

fixed output voltage values. If VOUT is above this voltage

value no switching occurs and only quiescent current is

drawn from the power source (sleep mode). When VOUT

drops below the fixed output voltage the LTC3106 “wakes

up”, switching commences, and the output capacitor is

again charged. The value of the output capacitor, the load

current, input source and the output voltage comparator

hysteresis(~1%)alldeterminethenumberofcurrentpulses

required to pump up the output capacitor before the part

returns to sleep. Normalized input and output voltages

in the various modes as well as typical inductor current

waveforms are shown in Figure 6. Only VIN is shown but

the VSTORE/VCAP power path have the same architecture.

Regions of the current waveforms where switches A and

D are on provide the highest efficiency since energy is

transferred directly from the input source to the output.

Boost Mode

When VIN < VOUT – 300mV, the LTC3106 operates in

boost or step-up mode. Referring to Figure 6 when VOUT

falls below the programmed regulation voltage, switches

A and C are turned on (VIN is applied across the induc-

tor) and current is ramped until IPEAK is detected. When

this occurs, C is turned off, D is turned on and current is

delivered to the output capacitor (VIN – VOUT is applied

across the inductor). Inductor current falls when D is on,

until an IVALLEY is detected. Terminating at IVALLEY results

in an increased load current capability for a given peak

current. This AC then AD switch sequence is repeated until

the output is pumped above the programmed regulation

voltage, a final IVALLEY is detected, and the part returns

to sleep mode.

Buck Mode

When VIN > VOUT + 700mV, the LTC3106 operates in buck

or step-down mode. At the beginning of a buck mode cycle

(Figure 6 right side) switches A and D are turned on (VIN

– VOUT is applied across the inductor), current is delivered

to the output and ramped up until IPEAK is detected. When

this occurs, A is turned off, B is turned on and inductor

current falls (–VOUT across the inductor) until an IVALLEY

is detected. This AD then BD switch sequence is repeated

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