LTC4013 datasheet(13/38 Pages) LINER

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LTC4013

4013fa

OPERATION

battery fault is indicated by STAT0 turning off and STAT1

turning on.

There are two voltage settings available for 2-stage charg-

ing as noted in Table 1.

2-stage charging for a lead-acid battery has the disad-

vantage of not fully charging the battery, resulting in

diminished capacity over time due to increased deposits

on the electrodes.

3-Stage Charging

A more complete lead-acid battery charging method is

3-stage charging utilizing an absorption phase which

increases the amount of stored charge in the battery.

Because the absorption voltage is above the electro-

chemical float level, the time that the battery stays in this

condition should be limited either by a timer (the safest

method) or waiting for the charge current to diminish.

Minor gassing of water from the battery can occur from

charging the battery above the float voltage, so choosing

an appropriate absorption voltage is important for best

battery life. Always consult the battery manufacturer for

their recommendations.

3-stagechargingisinitiatedoninputpower-upwhereupon

thebatterychargeswithconstant-currentatICHGMAXtoward

VFB(ABS). The STAT0 pin pulls low immediately indicating

thatcharginghasbegun.Asthebatteryvoltageapproaches

VFB(ABS), charge current naturally tapers to zero. When

the charge current drops to ICHGMAX/10, STAT1 also pulls

low and the charge voltage setting changes to the VFB(FL)

voltage. At this lower level, the constant-voltage control

loop will "capture" and hold the battery voltage as it slowly

drops from VFB(ABS) down to VFB(FL).

Alternately, the transition from absorption charging to

float charging can be controlled with the timer by placing

a capacitor on the TMR pin. When the battery voltage

reaches constant-voltage in the absorption phase, the

timer begins. At the end of the accumulated timer period

in constant-voltage mode at VFB(ABS), the charge voltage

changestotheVFB(FL)voltageandwillremainthere.Again,

STAT1 turns on, indicating the transition from the VFB(ABS)

charging level to the VFB(FL) charging level.

The LB pin provides a user adjustable low battery voltage

setting that sets the re-start level in 2-stage, 3-stage and

4-stage charging and the low battery fault level in Li-Ion

charging. The LB pin produces a precision 20µA current

whichresultsinaprecisionvoltagewhenaresistorisplaced

from LB to ground. The LB pin is compared internally to

the FB pin for low battery determination.

Four possible charging algorithms can be selected by pin

strapping or manipulating the MODE0 and MODE1 pins

(see Table 1). These pins should be tied either low (GND),

high (INTVCC) or mid (floating). The charge algorithms

are described below.

2-Stage Charging

2-stage charging is useful for batteries with no absorption

preconditioning. Charging is initiated on input power-up

whereupon the battery charges with constant-current

at ICHGMAX toward VFB(FL). The STAT0 pin pulls low im-

mediately indicating that charging has begun. Once the

battery terminals approach VFB(FL), the constant-voltage

control loop takes over holding the battery voltage steady

as the charge current naturally tapers to zero. Once the

constant-voltage loop takes control, the STAT1 pin also

pulls low indicating the change from constant-current to

constant-voltage charging.

If a capacitor is used on the TMR pin, the charge cycle

terminatesafteranaccumulatedperiodoftEOCinconstant-

voltage mode at which time STAT0 and STAT1 will indicate

termination by switching off. Alternately, if the TMR pin is

grounded, 2-stage charging will charge forever at VFB(FL)

with no termination.

Charging is re-initiated from termination if the FB-referred

battery voltage drops below the LB threshold voltage as

set by the LB pin, or if the LTC4013 is powered off and

back on by cycling the ENAB pin or input power.

Defective battery protection is enabled if the timer capaci-

tor is used. Whenever the FB-referred battery voltage is

below the LB threshold, charge current is automatically

reduced to ICHGMAX/5. If a defective battery remains below

the low battery threshold longer than 1/8 of the timer

period (tEOC/8) the charge cycle terminates. A defective

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