LTC4162EUFD-FST#PBF datasheet(30/52 Pages) AD

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LTC4162-F

Rev A

For more information www.analog.com

APPLICATIONS INFORMATION

TEMPERATURE (°C)

−1.0

−0.5

0.0

0.5

1.0

4162F F04

Thermistor: NTCS0402E3103FHT

NTCBIAS

=10k

SERIES

=549

PARALLEL

=187k

Figure 4. Residual Error from 0°C to 60°C for

β25/75 = 3950K Thermistor

For tools that can assist with alternate thermistors, please

visit the LTC4162 web page.

Programming the Input and Battery Charge Current

Limits

TheLTC4162featuresindependentresistorprogrammabil-

ity of the input current and battery charge current upper

limits to facilitate optimal charging from a wide variety of

inputpowersources.Thebatterychargecurrentshouldbe

programmed solely on the basis of the size of the battery

and its associated safe charging rate. Typically, this rate is

about "1C", or equal to the current which would discharge

the battery in one hour. For example, a 2000mAh battery

would be charged with no more than 2A. With the full

scale (default) charge current programmed via the resis-

tor, RSNSB, between CSP and CSN, all other selectable

charge current settings are lower and may be appropriate

for custom charge algorithms at extreme temperatures.

If the battery charge current limit requires more power

than is available from the selected input current limit, the

input current limit will be enforced and the battery will be

charged with less than the programmed current. Thus,

the battery charger sense resistor should be programmed

based on the battery capacity only, without concern for

the input source.

The maximum average input current is determined by

the sense resistor, RSNSI, connected between the CLP

and CLN pins. Its value should be chosen based only on

the maximum available current limit of the expected input

source. The input and charge current loops servo the volt-

agesacrosstheirrespectivesenseresistorstoamaximum

of 32mV, giving maximum input and charge currents of:

IIN(MAX) = 32mV/RSNSI

ICHG(MAX) = 32mV/RSNSB

The charge current and input current sense resistors con-

vertthechargeandinputcurrentsintoavoltagemeasurable

by the LTC4162. The accuracy and temperature coefficient

ofthecurrentsenseresistorscontributedirectlytothecur-

rent regulation accuracy of the LTC4162. While 4-terminal

resistors are available for current sensing applications,

simpler 2-terminal resistors provide a more economical

solution. Power dissipation of the sense resistors should

be carefully considered. For example, with a 3.2A charge

current the sense resistor would be 10mΩ and power

dissipation would be 3.2²A² • 10mΩ = 102.4mW. While

a 1/8W 0603 resistor is theoretically feasible in this ap-

plication, its temperature rise could be quite high. A 1/4W

to 1/2W 0805 resistor might be a better choice for lower

thermal rise and subsequently better accuracy. Using

larger copper pours and having more copper coverage

will reduce the thermal resistance of the sense resistors.

Figure 5 shows an example of a proper Kelvin connection

to the current sense resistors.

4162F F05

Figure 5. Kelvin Current Sensing with an 0805 Resistor.

LTC4162EUFD-FST#PBF Datasheet(PDF) 30 Page - Analog Devices

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