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AOZ1401DI Datasheet(PDF) 10 Page - Alpha & Omega Semiconductors |
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AOZ1401DI Datasheet(HTML) 10 Page - Alpha & Omega Semiconductors |
10 / 14 page AOZ1401DI Rev. 1.0 August 2011 www.aosmd.com Page 10 of 14 Theory of Operation The AOZ1401DI is an integrated Li+ charger protection IC that protects against input over-voltage, input over- current, and battery over-voltage conditions. When the device detects an input over-voltage condition, it turns off the internal MOSFET, preventing damage of the charger. When the device detects a battery over-voltage condition, it also turns off the internal MOSFET to prevent battery from being over-charged. In the case of an over-current condition, it limits the input current at the current limit level set by an external resistor, and if the over-current persists, it turns off the internal MOSFET after a blanking period. The thermal shutdown feature adds another layer of protection. The fault status indicator provides status information about fault conditions to the host. Under-Voltage Lockout (UVLO) The under-voltage lockout (UVLO) circuit of AOZ1401DI monitors the input voltage and prevents the output MOSFET from turning on until VIN exceeds 2.7V. Enable The ENB pin is the ON/OFF control for the output switch. When the ENB pin is driven high, the internal FET is turned off. When the ENB pin is low, the FET is turned on. Input Overvoltage Protection The device continuously monitors the input voltage, the input current, and the battery voltage. If the input voltage rises above VOVP, the internal FET is turned off, removing power from the circuit. When the input voltage returns below VOVP, but above VUVLO, the FET is turned on again after a deglitch time of tON (OVP) to ensure that the input supply has stabilized. Input Overcurrent Protection In the case of an over-current condition, AOZ1401DI limits the input current at the current limit level set by an external resistor, and if the over-current persists, it turns off the internal MOSFET after a blanking period. The overcurrent threshold is programmed by a resistor R5 (RILIM) connected from the ILIM pin to VSS. Figure 13 shows the OCP threshold as a function of R5 (RILIM), and may be approximated by the following equation: IOCP = 25 R5 (RILIM) (current in A, resistance in kΩ). Battery Over-voltage Protection The battery overvoltage threshold BVOVP is internally set to 4.35V. If the battery voltage exceeds the BVOVP threshold, the FET is turned off, and the FAULTB pin is driven low. FAULTB The FAULTB pin is an open drain output that is asserted low when either an input overvoltage, input overcurrent battery overvoltage, or thermal overload condition occurs. Thermal Shut-down Protection The thermal overload protection of AOZ1401DI is engaged to protect the device from damage should the die temperature exceeds safe margins due to a short circuit, extreme loading or heating from external sources. Application Information Input Capacitor Selection Use a 1μF or larger capacitor for input bypassing. This will limit the input voltage drop during output transient conditions. 1μF capacitor should be adequate for most applications; however, higher capacitor values will further reduce the voltage drop. Place the bypass capacitor as close to the IN pins as feasibly possible. Output Capacitor Selection Use a 1μF or larger capacitor between the OUT and GND pins. The capacitance does not affect the turn on slew rate; however, a larger capacitor will make the initial turn on transient smoother. Selection of R4 (RVBAT) Direct-connecting battery to VBAT is not recommended. The voltage at the IN pin may appear on the VBAT pin if IC fails. Connecting the VBAT pin through R4 (RVBAT) prevents a large current from flowing into the battery in case of a failure of the IC, so choose R4 (RVBAT) value in the range 100kΩ to 470kΩ. Selection of R3 (REN), R2 (RFAULTB), and R1 (RPU) The ENB pin can be used to enable and disable the IC. ENB pin can be tied to ground or left un-connected, permanently enabling the device, if host is not presented. If host control is required, the ENB pin should be connected to the host through as large a resistor as possible. The FAULTB pin is an open drain output that is asserted low when either an input overvoltage, input overcurrent battery overvoltage, or thermal overload condition occurs. If the application does not require monitoring of |
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