LTC4162EUFD-FST#PBF datasheet(19/52 Pages) AD

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LTC4162-F

Rev A

For more information www.analog.com

OPERATION

VOUT Voltage Measurement

Output voltage is measured through a 30.07:1 resistive

voltage divider making the A/D span term for system volt-

age measurements 30.07/18191 or 1.653mV/LSB and is

digitized to vout. An alert may be set on output voltage by

settingthevaluevout_lo_alert_limitorvout_hi_alert_limit

and setting en_vout_lo_alert or en_vout_hi_alert. These

alerts are indicated by vout_lo_alert and vout_hi_alert and

are cleared by writing them to 0.

Battery Current Measurement

Battery current is measured with a current sense resistor

between the CSP and CSN pins. An amplifier with a gain of

37.5 amplifies this signal and refers it to ground internally

so that the A/D converter can measure it. The sensed bat-

tery current is therefore given by IBAT • RSNSB • 37.5. For

a 10mΩ RSNSB current sense resistor, the A/D sensitivity

is 1/(18191 • 10mΩ • 37.5) or 146.6µA/LSB. The battery

current measurement system has a built in commutator.

While charging a battery, two's complement number ibat

willbepositiverepresentingcurrentintothebattery.When

the battery charger is disabled or terminated, as detected

by charger_suspended, the commutator is activated and

ibat will be negative, representing current out of the bat-

tery. An alert may be set on the ibat measurement by

setting the desired value in ibat_lo_alert_limit and setting

en_ibat_lo_alert. While charging, ibat_lo_alert_limit can

be used to detect when the charge current has dropped

below a given threshold. When charger_suspended, if set

to a negative number, ibat_lo_alert_limit can be used to

detect if the battery load has exceeded a given threshold.

This alert is indicated by ibat_lo_alert and is cleared by

writing it to 0.

Input Current Measurement

Input current is measured with a current sense resistor

between the CLP and CLN pins. An amplifier with a gain of

37.5 amplifies this signal and refers it to ground internally

so that the A/D converter can measure it. The sensed

input current is therefore given by IIN • RSNSI • 37.5. For

a 10mΩ RSNSI current sense resistor, the A/D sensitivity

is 1/(18191 • 10mΩ • 37.5) or 146.6µA/LSB. The input

current is digitized to iin. An upper limit alert may be set

on input current by setting the value iin_hi_alert_limit

and setting the en_iin_hi_alert. This alert is indicated by

iin_hi_alert and is cleared by writing it to 0.

Battery Series Resistance (BSR) Measurement

The LTC4162 can optionally measure the series resistance

of the battery stack or cell. If run_bsr is set, the LTC4162

momentarily suspends the battery charger and calculates

thebatteryseriesresistancebydividingthevoltagechange

(chargingvsnotcharging)bythemeasuredchargecurrent

(bsr_charge_current).

The per-cell resistance value is reported in bsr and the

charge current observed during the measurement is re-

portedinbsr_charge_current.TheLTC4162automatically

resets run_bsr after the bsr measurement is complete.

The total battery series resistance value is proportional to

the charge current sense resistor, RSNSB, as well as the

cell_count,andcanbecomputedinΩfromtheexpression:

RBAT(Ω) =

bsr • cell_ count • RSNSB

500

Higher bsr_charge_current during a bsr measurement

results in a more accurate bsr measurement. Very low

values of bsr_charge_current may adversely impact the

accuracy of the bsr measurement. If charge current is

less than C/10 (bsr_charge_current < icharge_over_10),

bsr_questionable will be set indicating that bsr_charge_

current during the bsr test was less than optimum for an

accurate reading. Recall that full charge current typically

flows at the beginning of a charge cycle (presuming the

battery is more deeply depleted) and will diminish when

the charger enters the constant voltage phase of charging.

Ifrun_bsrissetto1andthebatterychargerisnotcurrently

running, then the LTC4162 will be queued to perform the

bsr measurement only after the start of the next charge

cycle. An alert can be set with en_bsr_done_alert to

generate a bsr_done_alert interrupt indicating that a bsr

measurement is complete and that the result is available. A

bsr_hi_alert may also be set on battery series impedance

bywritingabsr_hi_alert_limitandsettingen_bsr_hi_alert.

Again, the bsr reading is the per-cell battery resistance

and should be scaled by cell_count or, consequently, the

LTC4162EUFD-FST#PBF Datasheet(PDF) 19 Page - Analog Devices

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