LTC4162EUFD-FST#PBF datasheet(20/52 Pages) AD

20 / 52 page

LTC4162-F

Rev A

For more information www.analog.com

OPERATION

target total resistance threshold for bsr_hi_alert_limit

should be divided by cell_count before being written to

bsr_hi_alert_limit.

bsr_done_alert and bsr_hi_alert are cleared by writing

them to 0.

Die Temperature Measurement

The LTC4162 has an integrated die temperature sensor

that is monitored by the A/D converter and is digitized to

die_temp. The die temperature is derived from an internal

circuit and follows the equation:

TDIE(°C) = die_temp • 0.0215°C/LSB – 264.4°C

An alert may be set on die temperature by setting the value

die_temp_hi_alert_limitandsettingen_die_temp_hi_alert.

This alert is indicated by die_temp_hi_alert and is cleared

by writing it to 0.

To set the die_temp_hi_alert_limit, compute the threshold

value from:

die _ temp _ hi_ alert _ limit =

TDIE(°C) +264.4°C

0.0215°C/LSB

Battery Temperature (NTC Thermistor) Measurement

To measure the battery temperature using a thermistor,

connect the thermistor, RNTC, normally being located in

the battery pack, between the NTC pin and ground, and a

low drift bias resistor, RNTCBIAS, between NTCBIAS and

NTC. RNTCBIAS should be a 1% or better resistor with a

value equal to the value of the chosen thermistor at 25°C

(R25).TheLTC4162appliesanexcitationvoltageof1.2Vto

RNTCBIAS to measure the thermistor value. The thermistor

measurement result is available at thermistor_voltage. To

minimize battery stress due to charging at temperature

extremes, the LTC4162 has both a simple and a more

advanced JEITA (Japan Electronics and Information

Technology Industries Association) temperature qualified

chargingalgorithm.Iftheapplicationdoesnotrequiretem-

peraturecontrolledcharging,thenthethermistorshouldbe

replaced with a resistor of equal value to the bias resistor

RNTCBIAStocontinuouslysimulate25°C.Ifthethermistoris

found to be open (thermistor_voltage > open_thermistor)

either during the battery detection test or during charg-

ing, charger_state will switch to bat_missing_fault and

charging will halt. Either a thermistor_voltage_lo_alert or

thermistor_voltage_hi_alert may be set with en_thermis-

tor_voltage_lo_alert or en_thermistor_voltage_hi_alert,

both of which are cleared by writing them to 0.

The temperature vs resistance curve of a thermistor can

be obtained from thermistor manufacturers in either table

form or estimated by applying the modified Steinhart-Hart

equation:

RNTC = R25 • e

(A+

TC+273.15

(TC+273.15)2

(TC+273.15)3

)

Where R25 is the thermistor's resistance at 25°C and A,

B, C and D are provided by the thermistor manufacturer

and TC is the temperature in °C.

The temperature of the thermistor is computed from its

resistance value by the complementary Steinhart-Hart

expression where A1, B1, C1 and D1 are also provided

by the thermistor manufacturer.

TC =

A1 +B1ln(

RNTC

R25

) + C1ln

2(RNTC

R25

) + D1ln

3(RNTC

R25

)

−273.15

(1)

Alternatively, the more common but less accurate con-

densed version of Steinhart-Hart using the ubiquitous β

parameter may be employed:

RNTC = R25 • e

−β25/85(

298.15oC

−

TC+273.15oC

)

Where again, R25 is the thermistor's resistance at 25°C

and several β values are provided by the thermistor manu-

facturer, one for each of a number of temperature ranges.

The inverse β form is:

TC =

β25/85

ln(

RNTC

R25

β25/85

298.15oC

– 273.15oC

(2)

LTC4162EUFD-FST#PBF Datasheet(PDF) 20 Page - Analog Devices

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