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LTC4061-4.4 Datasheet(PDF) 10 Page - Linear Technology |
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LTC4061-4.4 Datasheet(HTML) 10 Page - Linear Technology |
10 / 20 page LTC4061-4.4 10 406144fb 1 The Defective Battery Detection feature is only available when time termination is being used. 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 F C Hz CHRG TIMER = µ 0 1 6 . • ALEDdrivenbytheCHRGoutputexhibitsapulsingpattern, 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 CHRGpincapableofsinkingupto10mA.Apull-downstate indicatesthattheLTC4061-4.4ischargingabatteryandthe 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 100k Ω 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 approximately53k Ω,whichcorrespondstoapproximately 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 326k Ω, which corresponds to approximately 0°C.Thehotandcoldcomparatorseachhaveapproximately 2°Cofhysteresistopreventoscillationaboutthetrippoint. GroundingtheNTCpindisablestheNTCfunction.Formore details refer to the Application Information section. |
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