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LT3650-4.1 Datasheet(PDF) 7 Page - Linear Technology |
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LT3650-4.1 Datasheet(HTML) 7 Page - Linear Technology |
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7 / 20 page  LT3650-4.1/LT3650-4.2 7 36504142fb (full charge current) is the desired soft-start interval (tSS). For no RRNG/SS, this capacitor value follows the relation: CA t RNG SS SS / • = 50μ The RNG/SS pin is pulled low during fault conditions, allowing graceful recovery from faults should soft-start functionality be implemented. Both the soft-start capaci- tor and the programming resistor can be implemented in parallel. All C/10 monitoring functions are disabled while VRNG/SS is below 0.1V to accommodate long soft-start intervals. RNG/SS voltage can also be manipulated using an active device, employing a pull-down transistor to disable charge current or to dynamically servo maximum charge current. Manipulation of the RNG/SS pin with active devices that have low impedance pull-up capability is not allowed (see the Applications Information section). NTC (Pin 8): Battery Temperature Monitor Pin. This pin is the input to the NTC (negative temperature coefficient) thermistor temperature monitoring circuit. This function is enabled by connecting a 10k Ω, B = 3380 NTC thermistor from the NTC pin to ground. The pin sources 50μA, and monitors the voltage across the 10k Ω thermistor. When the voltage on this pin is above 1.36V (T < 0°C) or below 0.29V (T > 40°C), charging is disabled and the CHRG and FAULT pins are both pulled low. If internal timer termina- tion is being used, the timer is paused, suspending the charging cycle. Charging resumes when the voltage on NTC returns to within the 0.29V to 1.36V active region. There is approximately 5°C of temperature hysteresis associated with each of the temperature thresholds. The temperature monitoring function remains enabled while thermistor resistance to ground is less than 250k Ω, so if this function is not desired, leave the NTC pin unconnected. BAT (Pin 9): Battery Voltage Monitor Pin. Connect 10μF decoupling capacitance (CBAT) from this pin to ground. Depending on application requirements, larger value decoupling capacitors may be required (see the Applica- tion Information section). The charge function operates to achieve the final float voltage at this pin. The auto-restart feature initiates a new charging cycle when the voltage at the BAT pin falls 2.5% below this float voltage. Once the charge cycle is terminated, the input bias current of the BAT pin is reduced to <0.1μA, to minimize battery discharge while the charger remains connected. SENSE (Pin 10): Charge Current Sense Pin. Connect the more positive voltage end of the inductor sense resistor (RSENSE) to the SENSE pin and the other end to the BAT pin. The voltage across this resistor sets the average charge current. The maximum average charge current (IMAX) corresponds to 100mV across the sense resistor. This resistor can be set to program maximum charge currents as high as 2A. The sense resistor value follows the relation: R V I SENSE MAX = 01 . Once the charge cycle is terminated, the input bias current of the SENSE pin is reduced to <0.1μA, to minimize battery discharge while the charger remains connected. BOOST (Pin 11): Bootstrapped Supply Rail for Switch Drive. This pin facilitates saturation of the switch transistor. Connect a 1μF or greater capacitor from the BOOST pin to the SW pin. Operating range of this pin is 0V to 4.5V, referenced to the SW pin. The voltage on the decoupling capacitor is refreshed through a rectifying diode, with the anode connected to either the battery output voltage or an external source, and the cathode connected to the BOOST pin. SW (Pin 12): Switch Output Pin. This pin is the output of the charger switch, and corresponds to the emitter of the switch transistor. When enabled, the switch shorts the SW pin to the VIN supply. The drive circuitry for this switch is bootstrapped above the VIN supply using the BOOST supply pin, allowing saturation of the switch for maximum efficiency. The effective on-resistance of the boosted switch is 0.175 Ω. SGND (Pin 13): Ground Reference and Backside Exposed Lead Frame Thermal Connection. Solder the exposed lead frame to the PCB ground plane. PIN FUNCTIONS |
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