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LTC1760

1760fa

a) The programmed current cannot exceed the maximum

of the two requested currents + ILIMIT. This relaxed

limit enables accelerated charging if ILIMIT is greater

than the maximum of the two requested currents. For

the recommended matched battery pair the requested

current should be the same.

b) The programmed current cannot exceed ILIMIT

TURBO mode provides a mechanism for the SMBus Host

to enable the charge MUX to apply additional current to

both batteries. TURBO mode only has an effect when two

batteries are being charged simultaneously. TURBO mode

does not affect wake-up charging or any other conditions

that could inhibit charging. TURBO mode is entered when

LTC(TURBO) is set high.

Normally the LTC1760 will limit the current into both bat-

teries to the maximum of the two requested currents +

ILIMIT/32. TURBO mode removes this restriction, allowing

the charger to output as much as ILIMIT into the combined

battery system.

Forexample:InasystemwhereLTC(TURBO)=0,ILIMIT=4.0A

and each battery is requesting 2A the LTC1760 will not

output more than 2.125A into the combined battery system

or 1.06A into each battery if their charge states match.

In a system where LTC(TURBO)=1, ILIMIT= 4.0A and each

battery is requesting 2A the LTC1760 will now output up

to ILIMIT into the combined battery system or 2A into each

battery if their charge states match.

Even without TURBO mode, the LTC1760 offers signifi-

cantly reduced charge times for matched batteries in the

top-off state. This time savings is especially significant for

Lithium-Ion batteries. Simultaneously charging two bat-

teries reduces losses in switches and improves efficiency.

3.7 Controlled Charging Voltage Programming

The LTC1760 monitors the requested and actual voltages

in each battery and increments the programmed voltage

by 16mV each tQUERY unless one of the following condi-

tions are met:

a) The actual voltage exceeds the requested voltage in

either battery.

b) The actual voltage exceeds VLIMIT.

This is an extremely important feature of the LTC1760 since

it allows the charger to servo on the internal cell voltage

of the battery as determined by the Smart Battery. This

voltage may be significantly lower than the battery pack

terminal voltage which is used by all Level 2 chargers.

The advantage for the LTC1760 is improved charge time,

safety, and a more completely charged battery.

The voltage correction cannot exceed the minimum re-

quested voltage by more than 512mV. When decrementing,

the programmed voltage is reduced by 16mV each tQUERY.

Whenever changing conditions cause either battery to stop

charging, the voltage algorithm is reset to zero.

4 System Power Management Algorithm and Battery

Calibration

4.1 Turning Off System Power

The LTC1760 allows the user to turn off system power using

the LTC(POWER_OFF) bit. When POWER_OFF is asserted

high all power management functions are bypassed and

the LTC1760 will turn off DCIN, BAT2 and BAT1 power

paths. This feature allows the user to power down the

system. Charging is still allowed when POWER_OFF is

asserted high.

4.2 Power-By Algorithm When No Battery is Being

Calibrated

The LTC1760 will always attempt to maintain system power.

The preferred configuration is to remain in 3- Diode mode.

In 3-Diode mode, power will be provided by BAT1, BAT2

and DCIN with the source at the highest voltage potential

automatically providing all the power. Sources at similar

voltage potentials will share power based on their capacity.

The following conditions will cause the LTC1760 to modify

its preferred power-by algorithm.

1. A battery issues a TERMINATE_DISCHARGE alarm and

AC_PRESENT is high. The LTC1760 will select the other

battery and DCIN to power the system.

OPERATION

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