LT3650-4.1/LT3650-4.2

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Status Pins

The LT3650 reports charger status through two open-col-

lector outputs, the CHRG and FAULT pins. These pins can

when enabled.

The CHRG pin indicates that the charger is delivering

current at greater than a C/10 rate, or one-tenth of the

programmed 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 the pin pulled low, and Off indicates pin high

impedance:

voltage is achieved, the charge current falls until the C/10

threshold is reached, at which time the charger terminates

and the LT3650 enters standby mode. The CHRG status

pin follows the charger cycle and is high impedance when

the charger is not actively charging.

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 LT3650 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

Timer EOC is typically set to three hours, which requires

a 0.68μF capacitor.

The CHRG status pin continues to signal charging at a

C/10 rate, regardless of which termination scheme is

used. When timer termination is used, the CHRG status

pin is pulled low during a charging cycle until the charger

output current falls below the C/10 threshold. The charger

continues to top off the battery until timer EOC, when the

LT3650 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 occurs when the battery is charged to within 2.5%

of the full-charge float voltage. If a charge cycle is not

successful at EOC, the timer cycle resets and charging

continues for another full timer cycle.

voltage, whether by battery loading or replacement of

the battery, the charger automatically re-engages and

starts charging.

APPLICATIONS INFORMATION

Table 1. Status Pins State Table

STATUS PINS STATE

CHARGER STATUS

CHRG

FAULT

Off

Off

Not Charging—Standby or Shutdown Mode

Off

On

Bad-Battery Fault

(Precondition Timeout/EOC Failure)

On

Off

Normal Charging at C/10 or Greater

On

On

NTC Fault (Pause)

If the battery is removed from an LT3650 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 LT3650 supports a low current based termination

scheme, where a battery charge cycle terminates when

the current output from the charger falls to below one-

The C/10 threshold current corresponds to 10mV across

the TIMER pin to ground.

When C/10 termination is used, an LT3650 charger sources

battery charge current as long as the average current level

remains above the C/10 threshold. As the full-charge float