LTC4160 datasheet(18/32 Pages) LINER

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LTC4160/LTC4160-1

41601f

the battery will eventually self discharge. To ensure that

the battery is always topped off, a charge cycle will auto-

matically begin when the battery voltage falls below the

recharge threshold which is typically 100mV less than

the charger’s ﬂoat voltage. In the event that the safety

timer is running when the battery voltage falls below the

recharge threshold, it will reset back to zero. To prevent

brief excursions below the recharge threshold from reset-

ting the safety timer, the battery voltage must be below

the recharge threshold for more than 1ms. The charge

cycle and safety timer will also restart if the VBUS UVLO

cycles low and then high (e.g., VBUS is removed and then

replaced), or if the battery charger is cycled on and off by

the ENCHARGER pin.

Charge Current

The charge current is programmed using a single resis-

tor from PROG to ground. 1/1030th of the battery charge

current is sent to PROG, which will attempt to servo to

1.000V. Thus, the battery charge current will try to reach

1030 times the current in the PROG pin. The program

resistor and the charge current are calculated using the

following equation:

CHG

PROG

• 1030

In either the constant-current or constant-voltage charging

modes, the voltage at the PROG pin will be proportional to

the actual charge current delivered to the battery. There-

fore, the actual charge current can be determined at any

time by monitoring the PROG pin voltage and using the

following equation:

BAT

PROG

•1030

In many cases, the actual battery charge current, IBAT, will

be lower than ICHG due to limited input power available and

prioritization with the system load drawn from VOUT.

The Battery Charger Flow Chart on the next page illustrates

the battery charger’s algorithm.

Charge Status Indication

The CHRG and FAULT pins can be used to indicate the status

of the battery charger. Two possible states are represented

by CHRG: charging and not charging. An open-drain output,

the CHRG pin can drive an indicator LED through a current

limiting resistor for human interfacing or simply a pull-up

resistor for microprocessor interfacing.

When charging begins, CHRG is pulled low and remains

low for the duration of a normal charge cycle. When charg-

ing is complete, i.e., the BAT pin reaches the ﬂoat and the

charge current has dropped to one tenth of the programmed

value, the CHRG pin goes high. The CHRG pin does not

respond to the C/10 threshold if the LTC4160/LTC4160-1

is in VBUS input current limit. This prevents false end-of-

charge indications due to insufﬁcient power available to

the battery charger.

Table 2 illustrates the possible states of the CHRG and

FAULT pins when the battery charger is active.

Table 2. Charge Status Readings Using the CHRG and FAULT Pins

STATUS

CHRG

FAULT

Charging/NTC Fault

Low

High

Not Charging

High

Bad Battery

High

Low

An NTC fault pauses charging while the battery tempera-

ture is out of range but is not indicated using the CHRG

or FAULT pins.

If a battery is found to be unresponsive to charging (i.e.,

its voltage remains below 2.85V for 1/2 hour) the CHRG

pin goes high and the FAULT pin goes low to indicate a

bad battery fault.

Note that the LTC4160/LTC4160-1 are 3-terminal

PowerPath products where system load is always priori-

tized over battery charging. Due to excessive system load,

there may not be sufﬁcient power to charge the battery

beyond the trickle charge threshold voltage within the bad

battery timeout period. In this case, the battery charger

will falsely indicate a bad battery. System software may

then reduce the load and reset the battery charger to try

again.

The FAULT pin is also used to indicate whether there is

a short circuit condition on VBUS when the bidirectional

OPERATION

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