LTC4061EDD-TRPBF View Datasheet(PDF) - Linear Technology

Part Name

Description

MFG CO.

LTC4061EDD-TRPBF

Standalone Linear Li-Ion Battery Charger with Thermistor Input

Linear Technology 

LTC4061

Operation

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 current

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

indicates the FAULT state by driving the CHRG open-drain

output with a square wave. The duty cycle of this oscillation

is 50% and the frequency is set by CTIMER:

f CHRG

=

0.1µF

CTIMER

• 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 pull-down

state, an NMOS transistor pulls down on the CHRG pin

10

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

that the LTC4061 is charging a battery and the charge cur-

rent is greater than IDETECT (which is set by the external

component 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 is not charging.

Smart Pulsing Error Feature

LTC4061 has two different pulsing states at CHRG pull-

down pin:

1. 6Hz (50% duty cycle) due to defective battery detection

(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 NTH-

S0603N01N1003J thermistor). The LTC4061 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 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.

4061fd

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