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LTC3106

3106f

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until the output is pumped above its regulation voltage, a

finalIVALLEYisdetected,andthepartreturnstosleepmode.

Buck-Boost Mode

If (VOUT – 700mV) < VIN < (VOUT + 300mV), the LTC3106

operates in 4-switch step-up/step-down mode. Returning

to Figure 6 (center) when VOUT falls below its regulation

voltage, switches A and C are turned on and current is

ramped until IPEAK is detected. As with boost mode opera-

tion, C is then turned off, D is turned on and current is

delivered to the output. When A and D are on, the inductor

current slope is dependent on the relationship between

VIN, VOUT, and the RDS(ON) of the switches. In 4-switch

mode, a tOFF timer is used to terminate the AD pulse.

Once the tOFF timer expires, switch A is turned off, B is

turned on, inductor current is ramped down and VOUT is

applied across the inductor until IVALLEY is detected. This

sequence is repeated until the output is regulated, BD

switches are turned on, and a final IVALLEY is detected.

Anti-cross conduction circuitry in all modes ensures the

P-channel MOSFET and N-channel MOSFET switch pairs

(A and B or D and C) are never turned on simultaneously.

Note all three operational modes function the same if pow-

ering from VSTORE/VCAP when VIN is not available. Simply

consider VIN in the preceding paragraphs as VSTORE/VCAP.

Undervoltage Lockout (UVLO)

and Very Low VIN Operation

There is an undervoltage lockout (UVLO) circuit within

the LTC3106 to allow very low voltage VIN operation.

If the LTC3106 is configured so that the RUN pin is

externally driven to a voltage greater than the 600mV ac-

curate RUN threshold, the VIN UVLO function allows the

input voltage to remain viable as an input source down

to ~250mV. Below this threshold VIN is disabled and the

input source will transition to VSTORE/VCAP, assuming

VSTORE/VCAPiswithinitsprogrammedrange,untilVINrises

above ~300mV, where input power again transitions to

VIN. The VIN input is always given priority over the VSTORE/

VCAP input if VIN is viable.

operaTion

Figure 7. MPP Configurations

Maximum Power Point Operation

As an alternative to using an external divider on the RUN

pin (or for maximum power point thresholds below the

600mVRUNpinthreshold)themaximumpowerpointcon-

trol circuit allows the user to set the optimal input voltage

operating point for a given power source. The MPP circuit

hysteretically regulates the average VINvoltagetotheMPP

threshold. When VINisgreaterthantheMPPvoltage,input

power is taken from VINtosupplytheload.IftheVINpower

source does not have enough power for the load it will

decrease. When VINislessthantheMPPthresholdvoltage

the input transitions to VSTORE/VCAPifavailable.VINpower

maythenrechargetheinputcapacitorvoltageandasitrises

above the MPP threshold the process repeats. VIN MPP

regulation is then maintained using this “burst” technique.

If VSTORE is disabled or in undervoltage, no switching

occurs until VIN again rises above the MPP threshold and

only quiescent current is drawn from the power source

(same as sleep mode).

To set the MPP threshold a 1.5µA (typical) source current

is provided at the MPP pin. An external resistor to ground

allows an arbitrary MPP threshold voltage setting. See

Figure 7.

MPP

1.2µA

3106 F07

LTC3106

IQ = 10.5µA

MPP FUNCION

ENABLED

MPP

VCC

LTC3106

IQ = 1.5µA

MPP FUNCION

DISABLED

Note that when the MPP function is used the nominal

quiescentcurrentincreasesfrom1.5µA(typical)to10.5µA

(typical). To disable the MPP feature and eliminate the

additional IQ, simply tie MPP to VCC.

PGOOD Comparator

The LTC3106 provides an open-drain PGOOD output that

pulls low if VOUT falls more than 10% (typical) below its

programmedvalue.WhenVOUTrisestowithin8%(typical)

of its programmed value, the internal PGOOD pull-down

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