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LT3652

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Status Pins

The LT3652 reports charger status through two open

collector outputs, the CHRG and FAULT pins. These pins

can accept voltages as high as VIN, and can sink up to

10mA when enabled.

The CHRG pin indicates that the charger is delivering

current at greater that a C/10 rate, or 1/10th of the pro-

grammed maximum charge current. The FAULT pin signals

bad battery and NTC faults. These pins are binary coded,

and signal following the table below, where ON indicates

pin pulled low, and OFF indicates pin high-impedance:

STATUS PINS STATE

CHARGER STATUS

CHRG

FAULT

OFF

Not Charging — Standby or Shutdown Mode

OFF

Bad Battery Fault (Precondition Timeout / EOC

Failure)

OFF

Normal Charging at C/10 or Greater

NTC Fault (Pause)

If the battery is removed from an LT3652 charger that is

configured for C/10 termination, a sawtooth waveform

of approximately 100mV appears at the charger output,

due to cycling between termination and recharge events,

This cycling results in pulsing at the CHRG output. An

LED connected to this pin will exhibit a blinking pattern,

indicating to the user that a battery is not present. The

frequency of this blinking pattern is dependent on the

output capacitance.

C/10 Termination

The LT3652 supports a low-current based termination

scheme, where a battery charge cycle terminates when the

current output from the charger falls to below one-tenth

of the maximum current, as programmed with RSENSE.

The C/10 threshold current corresponds to 10mV across

RSENSE. This termination mode is engaged by shorting

the TIMER pin to ground.

APPLICATIONS INFORMATION

When C/10 termination is used, a LT3652 charger will

source battery charge current as long as the average

current level remains above the C/10 threshold. As the

full-charge float voltage is achieved, the charge current

falls until the C/10 threshold is reached, at which time the

charger terminates and the LT3652 enters standby mode.

The CHRG status pin follows the charger cycle, and is high

impedance when the charger is not actively charging.

When VBAT drops below 97.5% of the full-charged float

voltage, whether by battery loading or replacement of the

battery, the charger automatically re-engages and starts

charging.

There is no provision for bad battery detection if C/10

termination is used.

Timer Termination

The LT3652 supports a timer based termination scheme, in

which a battery charge cycle is terminated after a specific

amount of time elapses. Timer termination is engaged

when a capacitor (CTIMER) is connected from the TIMER

pin to ground. The timer cycle EOC (TEOC) occurs based

on CTIMER following the relation:

CTIMER = TEOC • 2.27 x 10–7

(Hours)

Timer EOC is typically set to 3 hours, which requires a

0.68μF capacitor.

The CHRG status pin continues to signal charging at a C/10

rate, regardless of what termination scheme is used. When

timer termination is used, the CHRG status pin is pulled

low during a charging cycle until the charger output cur-

rent falls below the C/10 threshold. The charger continues

to top-off the battery until timer EOC, when the LT3652

terminates the charging cycle and enters standby mode.

Termination at the end of the timer cycle only occurs if

the charging cycle was successful. A successful charge

cycle is when the battery is charged to within 2.5% of the

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