LTC4012 datasheet(23/48 Pages) AD

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LTC4162-S

Rev B

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OPERATION

Battery Voltage Selection

The LTC4162 can charge either a 6V battery, a 12V battery,

an 18V battery or a 24V battery by pin strapping the

CELLS0/CELLS1 pins. CELLS1 and CELLS0 should be pin

strapped to either GND, VCC2P5, or INTVCC to make the

battery voltage selection (see Table 5). For added safety,

cell_count can be read back from the I2C port. cell_count

will read back 2 for every multiple of 6V selected. Any

combination of pins not shown in Table 5 will result in a

cell_count_err and will inhibit charging.

Table 5. CELLS0 and CELLS1 Pin Mapping to Battery Voltage

CELLS1

CELLS0

Battery

Voltage

Physical

Cell Count

cell_count

INTVCC

VCC2P5

12V

INTVCC

GND

18V

VCC2P5

INTVCC

24V

When charging stacks of batteries in series it is important

to consult with the battery manufacturer to ascertain

requirements pertaining to battery balancing. Repeatedly

charging series batteries without balancing is usually

degenerative and typically leads to increased mismatch

accompanied with shorter battery life. For high reliability

applicationsanauxiliarybatterybalancerisrecommended.

Battery Detection

The LTC4162 begins a charging cycle by performing a 2-4

second battery detection test, during which a 1mA load is

drawn from the battery followed by a small charge current

beingsenttothebattery.Ifthebatteryvoltageremainssta-

bleduringthebatterydetectiontest,theLTC4162proceeds

with battery charger soft-start. If the battery voltage does

not remain stable, the LTC4162 proceeds with a battery

open/shorttest.Thebatteryischargedatminimumcharge

current for one to two seconds. Abnormal results from the

batterydetectiontestresultincharger_statebecomingbat_

missing_fault, bat_short_fault or bat_detect_failed_fault

andwillpreventfurthercharging.Programmableinterrupts

en_bat_short_fault_alert,en_bat_missing_fault_alertand

en_bat_detect_failed_fault_alert can be set to generate an

SMBALERT if one of these cases occurs. In the event of a

battery detection fault, the battery detection test will retry

every 30 seconds.

Battery Charger Soft-Start

The LTC4162 soft starts charge current by ramping ich-

arge_dac from 0 to its target charge current setting at a

nominal rate of 400µS per icharge_dac LSB. This results

in a maximum charge current soft start time of 31 • 400µs

or 12.4ms. Any time the battery charger needs to change

its charge current setting up or down, the ramp routine

is invoked. The charge current target is derived from

charge_current_setting.

Low Battery

Whenachargecyclebegins,TheLTC4162firstdetermines

if the battery is deeply discharged. If the BATSENS+ pin

voltage is lower than about 2.5V, the battery charger de-

livers roughly 10mA directly from INTVCC. This operating

mode is mainly used to pull a pack protected battery out of

protectionmode.WhentheBATSENS+pinvoltagereaches

2.5V,charginghandsovertotheswitchingbatterycharger.

Constant-Current Charging

The charger will attempt to deliver (charge_current_set-

ting + 1) • 1mV/RSNSB in constant-current mode where

charge_current_setting ranges from 0 to 31. For example,

A 10mΩ resistor between CPS and CSN would give an

upper limit charge current of 3.2A. Depending on avail-

able input power and external load conditions, the battery

charger may not be able to charge at the full programmed

rate. An alternate control loop such as the input current

limit loop or input voltage limit loop may be in force and

only partial power will be available to charge the battery.

If input current limit is reached, for instance, the system

load will be prioritized over the battery charge current.

When system loads are light, battery charge current will be

maximized and could be as high as the value programmed

by charge_current_setting.

LTC4012 Datasheet(PDF) 23 Page - Analog Devices

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