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AP2403 Datasheet(PDF) 8 Page - Asahi Kasei Microsystems |
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AP2403 Datasheet(HTML) 8 Page - Asahi Kasei Microsystems |
8 / 20 page [AP2403] MS1528-E-02 2014/01 - 8 - 9. Functional Descriptions 1. Shutdown The AP2403 is in shutdown condition when a Low signal is input to the PWON pin even if power supply was input to the VIN pin. When a High signal is input to the PWON pin, the AP2403 is powered up in soft-start mode. 2. Soft Start Mode: This function prevents an overshoot of the output voltage when the AP2403 is powered up. It controls the output voltage slowly. During the soft-start period a capacitor connected to the SS pin is charged from 0V to 1.0V by a 20A constant current. In soft start, an output voltage rising is controlled by changing the over-voltage limitation value linearly in accordance with the SS pin voltage. When this function starts, the over-current limitation value is fixed in 50% (2.25A typ.). It changes linearly during the period which the SS pin voltage increases to 1.0V from 0.5V. When a soft start operation is completed, the AP2403 shifts to a PWM control. 3. Constant Voltage Operation: The AP2403 operates by Current-mode PWM controls. It determines the target value of inductance current by amplifying the voltage difference between the FB pin and 0.6V which is feedback reference voltage. The internal P-channel MOSFET is powered on until the inductance current meets the target value. When the inductance current reaches the target value, the built-in P-channel MOSFET becomes OFF and the built-in N-channel MOSFET becomes ON. Then the AP2403 operates in synchronous rectification mode. 4. Prevention of Incorrect Operation in Low Voltage (UVLO: Under Voltage Lock Out): When the V5 pin voltage becomes less than 2.5V by a main power supply voltage decrease, all circuit blocks in the AP2403 are stopped and the AP2403 becomes UVLO state. The UVLO state has hysteresis, and the AP2403 keeps UVLO state until the main power supply voltage rises again and exceeds 2.5V. When the UVLO state is released, the AP2403 restarts by a soft start operation. 5. Output Over-Voltage Protection (OVP): When the output voltage becomes +30% or more of the setting value, the built-in P-channel MOSFET and the built-in N-channel MOSFET become OFF state and the AP2403 enters protection mode. This state is maintained until the built-in P-channel MOSFET is turned on by the FB amplifier. The AP2403 is in normal operation when recovering from the output over-voltage protection. It does not shift to soft-start mode. 6. Hiccup type Output Over-Current Limitation (OCL): This function reduces the output voltage and the output current by Hiccup operation in an over-current condition. When the over-current condition is detected, the built-in P-channel MOSFET and the built-in N-channel MOSFET become OFF and the SS pin voltage which is 1.0V discharged from 1.0V to 0.4V by a continuous current of 1.0uA. The AP2403 stops its operation without shifting to a soft start operation in this discharging period of the SS pin. When the SS pin voltage decreases to 0.4V, the AP2403 enters a soft start operation after the SS pin voltage is discharged further to the GND level by the internal switch. The AP2403 repeats this sequence until the over current condition is removed. |
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