LTC4061-4.4 데이터 시트보기 (PDF) - Linear Technology

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LTC4061-4.4

Standalone Linear Li-Ion Battery Charger with Thermistor Input

Linear Technology 

LTC4061-4.4

U

OPERATIO

Undervoltage Lockout (UVLO)

An internal undervoltage lockout circuit monitors the

input voltage and keeps the charger in shutdown mode

until VCC rises above the undervoltage lockout threshold

(3.8V). The UVLO circuit has a built-in hysteresis of

200mV. Furthermore, to protect against reverse current in

the power MOSFET, the UVLO circuit keeps the charger in

shutdown mode if VCC falls to less than 45mV above the

battery voltage. Hysteresis of 145mV prevents the charger

from cycling in and out of shutdown.

Manual Shutdown

At any point in the charge cycle, the charger can be put

into shutdown mode by pulling the EN pin high. This

reduces the supply current to less than 50µA and the

battery drain current of the charger to less than 2µA. A

new charge cycle can be initiated by floating the EN pin

or pulling it low.

If shutdown is not required, leaving the pin disconnected

continuously enables the circuit.

Trickle-Charge and Defective Battery Detection

When the BAT pin voltage is below the 2.9V trickle charge

threshold (VTRIKL), the charger reduces the charge cur-

rent to 10% of the programmed value. If the battery

remains in trickle charge for more than 25% of the total

programmed charge time, the charger stops charging

and enters a FAULT state, indicating that the battery is

defective1. The LTC4061-4.4 indicates the FAULT state by

driving the CHRG open-drain output with a square wave.

The duty cycle of this waveform is 50% and the frequency

is set by CTIMER:

f CHRG

=

0.1µF

C TIMER

• 6Hz

A LED driven by the CHRG output exhibits a pulsing pattern,

indicating to the user that the battery needs replacing. To

exit the FAULT state, the charger must be restarted either

by toggling the EN input or removing and reapplying

power to VCC.

Charge Status Output (CHRG)

The charge status indicator pin has three states: pull-

down, pulse at 1.5Hz or 6Hz and high impedance. In the

10

pull-down state, an NMOS transistor pulls down on the

CHRG pin capable of sinking up to 10mA. A pull-down state

indicates that the LTC4061-4.4 is charging a battery and the

charge current is greater than IDETECT (which is set by the

external resistor RDET). A high impedance state indicates

that the charge current has dropped below IDETECT. In the

case where the IDET pin is left unconnected (RDET = ∞,

IDETECT = 0), a high impedance state on CHRG indicates

that the LTC4061-4.4 is not charging.

Smart Pulsing Error Feature

The CHRG pin has two different pulsing states.

1) 6Hz (50% duty cycle) due to defective battery detec-

tion (see Trickle-Charge and Defective Battery Detection

section);

2) 1.5Hz (25% duty cycle if in time termination, 50% duty

cycle if in charge current or user termination) due to NTC

out-of-temperature condition.

NTC Thermistor (NTC)

The temperature of the battery is measured by placing

a negative temperature coefficient (NTC) thermistor

close to the battery pack. The NTC circuitry is shown in

Figure 1. To use this feature, connect the NTC thermistor,

RNTC, between the NTC pin and ground and a resistor,

RNOM, from the NTC pin to VCC. RNOM should be a 1%

resistor with a value equal to the value of the chosen

NTC thermistor at 25°C (this value is 100kΩ for a Vishay

NTHS0603N01N1003J thermistor). The LTC4061-4.4

goes into hold mode when the resistance, RHOT, of the

NTC thermistor drops to 0.53 times the value of RNOM or

approximately 53kΩ, which corresponds to approximately

40°C. Hold mode freezes the timer and stops the charge

cycle until the thermistor indicates a return to a valid

temperature. As the temperature drops, the resistance of

the NTC thermistor rises. The LTC4061-4.4 is designed to

go into hold mode when the value of the NTC thermistor

increases to 3.26 times the value of RNOM. This resistance

is RCOLD. For a Vishay NTHS0603N01N1003J thermistor,

this value is 326kΩ, which corresponds to approximately

0°C. The hot and cold comparators each have approximately

2°C of hysteresis to prevent oscillation about the trip point.

Grounding the NTC pin disables the NTC function. For more

details refer to the Application Information section.

1 The Defective Battery Detection feature is only available when time termination is being used.

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