LTC4162EUFD-FST#PBF datasheet(17/52 Pages) AD

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LTC4162-F

Rev A

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OPERATION

temperature compensated charge voltages and currents,

maximum power point tracking, charger soft starting,

etc. The target value registers are read/write whereas the

actual DAC value registers, icharge_dac, vcharge_dac,

iin_limit_dac and input_undervoltage_dac are read only.

Due to its all NMOS switch design, a small charge pump

capacitor is required from SW to BOOST to provide high

side boosted drive for the top switch.

Input Current Regulation

Input current control limits loading on the input source

duringperiodsofhighsystemdemandbysacrificingcharge

current. Note that the LTC4162 only has the authority to

reduce charge current to zero and cannot further reduce

input current below the system load current. The input

current limit is controlled by a combination of the sense

resistor, RSNSI, from CLP to CLN and either the default

32mVservovoltageoralowervaluesetbyiin_limit_target.

The servo voltage across the sense resistor divided by the

resistor's value determines the input current regulation

set point. A 10mΩ resistor, for example, would have an

upper input current limit of 3.2A using the default 32mV

servo voltage. iin_limit_target has 6 bit resolution giving

adjustable values from 500µV to 32mV in 500µV steps and

can be calculated in Amperes, by the following expression:

IINLIM = (iin _ limit _ target + 1)

500μV

RSNSI

whereiin_limit_targetrangesfromintegervaluesof0to63.

Input Undervoltage Regulation and Solar Panel

Maximum Power Point Tracking (MPPT)

The LTC4162 also contains an undervoltage control loop

that allows it to tolerate a resistive connection to the input

power source by automatically reducing charge current

as the VIN pin drops to input_undervoltage_setting. This

circuit helps prevent UVLO oscillations by linearly regulat-

ing the input voltage above the LTC4162's undervoltage

lockout level.

Optionally, the LTC4162 includes a maximum power

point tracking (MPPT) algorithm to find and track the

input_undervoltage_dac value that delivers the maximum

charge current to the battery. If mppt_en is set, the MPPT

algorithm performs a global sweep of input_undervolt-

age_dac values, measuring battery charge current at each

setting. Once the sweep is complete, the LTC4162 applies

the input_undervoltage_dac value corresponding to the

maximum battery charge current ibat (i.e. the maximum

power point). The LTC4162 then tracks small changes

in the maximum power point by slowly dithering the

input_undervoltage_dac. The LTC4162 performs a new

global sweep of input_undervoltage_dac values every

15 minutes, applies the new maximum power point, and

resumes dithering at that point. Alternatively, the global

sweep will run immediately, bypassing the 15 minute wait,

if ibat changes by more that 25%. With mppt_en, a solar

panel can be used as a suitable power source for charg-

ing a battery and powering a load. The MPPT algorithm

may not work for all solar panel applications and does not

have to be used. Alternatively a solar panel can be used

without the MPPT algorithm by setting the input_under-

voltage_setting value to match the optimum loaded solar

panel voltage, but significant shadows or drops in light

will likely result in suboptimum power delivery.

Notethat,duetothePowerPathtopology,currentcanflow

from the input to the system load without being controlled

by the LTC4162's switching charger. Therefore, the MPPT

algorithm does not have full authority to track and find

the maximum power point under all conditions. To obtain

complete Maximum Power Point operation, it may be

necessary to forgo the Power Path feature of the LTC4162

and connect the system load directly to the battery pack. In

this configuration, the LTC4162 has full authority to track

the maximum power point of the solar panel.

The input under voltage value, in Volts, will be given by

the following expression:

VINLIM=(input_undervoltage_setting+1)•140.625mV

where input_undervoltage_setting ranges from integer

values of 0 to 255.

LTC4162EUFD-FST#PBF Datasheet(PDF) 17 Page - Analog Devices

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