LTC3130 datasheet(21/38 Pages) LINER

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LTC3130/LTC3130-1

3130f

For more information www.linear.com/LTC3130

OPERATION

Figure 4. MPPC Amplifier with External Resistor Divider

LTC3130

1.0V

CURRENT

COMMAND

VOLTAGE

ERROR AMP

3130 F04

MPPC

VSOURCE

CIN

VIN

–

nuisance trips of PGOOD due to short transients on VOUT.

PGOOD can be pulled up to any voltage, as long as the

absolute maximum rating of 25V is not exceeded, and

as long as the absolute maximum sink current rating of

12mA is not exceeded when PGOOD is low.

NotethatPGOODwillbedrivenlowifVCCisbelowitsUVLO

threshold or if the part is in shutdown (RUN below its logic

threshold). PGOOD is not affected by the accurate RUN

threshold. Therefore, if PGOOD is pulled up to VIN or VCC,

this will add to the VIN quiescent current in shutdown and

UVLO, when PGOOD is low. For the lowest possible VIN

current in shutdown or UVLO, PGOOD should be pulled

up to VOUT or some other source.

Maximum Power Point Control (MPPC)

The MPPC input of the LTC3130/LTC3130-1 can be used

with an optional external voltage divider to dynamically

adjust the commanded inductor current in order to main-

tain a minimum input voltage when using high resistance

sources, such as photovoltaic panels, so as to maximize

input power transfer and prevent VIN from dropping too

low under load.

Referring to Figure 4, the MPPC pin is internally connected

to the noninverting input of a gm amplifier, whose invert-

ing input is connected to the 1.0V reference. If the voltage

at MPPC, using the external voltage divider, falls below

the reference voltage, the output of the amplifier pulls

the internal VC node low. This reduces the commanded

average inductor current so as to reduce the input current

and regulate VIN to the programmed minimum voltage,

as given by:

VIN(MPPC) =1.00V • 1+









Note that external compensation should not be required

for MPPC loop stability if the input filter capacitor, CIN,

is at least 22µF.

The MPPC divider resistor values can be in the MΩ range

so as to minimize the input current in very low power ap-

plications. However, stray capacitance and noise pickup

on the MPPC pin must also be minimized. If the MPPC

functionisnotrequired,theMPPCpinshouldbetiedtoVCC.

Beware of adding a noise filter capacitor to the MPPC pin,

as the added filter pole may cause the MPPC control loop

to be unstable.

Note that because Burst Mode operation will be inhibited

if the MPPC loop takes control, the converter will be op-

erating in fixed frequency mode, and will therefore require

a minimum of about 6mA of continuous input current to

operate.Foroperationfromweakersources,suchassmall

indoor solar panels, refer to the Applications Information

section to see how the RUN pin may be programmed to

control the converter in a hysteretic manner while provid-

ing an effective MPPC function by maintaining VIN at the

desired voltage. This technique can be used with sources

as weak as 3µA (enough to power the IC in UVLO and the

external RUN divider).

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