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VLCF4020-6R8 Datasheet(PDF) 11 Page - ON Semiconductor |
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VLCF4020-6R8 Datasheet(HTML) 11 Page - ON Semiconductor |
11 / 16 page NCP1511 http://onsemi.com 11 Table 1. Operating Mode Selection SYNC Pin State Operating Mode LOW Pulsed Mode (PM) HIGH PWM, 1 MHz Switch Frequency CLOCK PWM, Frequency Synchronization Output Voltage Selection The output voltage is digitally programmed to one of four voltage levels depending on the logic state of CB0 and CB1. Therefore if the NCP1511’s load, such as a digital cellular phone’s baseband processor, supports dynamic power management, the device can lower or raise its core voltage under software control. When combined with the pulsed current mode function in low load situations, this active voltage management further stretches the useful operating life of the handset battery between charges. The output voltage levels are listed in Table 2. The CB0 has a pull down resistor and the CB1 has a pullup resistor. The default output voltage is 1.3 V when CB0 and CB1 are floating. Table 2. Truth Table for CB0 and CB1 with the Corresponding Output Voltage CB0 CB1 Vout(V) 0 0 1.0 0 1 1.3 1 1 1.5 1 0 1.89 Soft−Start The NCP1511 uses soft−start to limit the inrush current when the device is initially powered up or enabled. Soft−start is implemented by gradually increasing the reference voltage until it reaches the full reference voltage. During startup, a pulsed current source charges the internal soft−start capacitor to provide gradually increasing reference voltage for the PWM loop. When the voltage across the capacitor ramps up to the nominal reference voltage, the pulsed current source will be switched off and the reference voltage will switch to the regular reference voltage. Shutdown Mode When the SHD pin has a voltage applied of less than 0.4 V, the NCP1511 will be disabled. In shutdown mode, the internal reference, oscillator and most of the control circuitries are turned off. Therefore, the typical current consumption will be 0.1 mA (typical value). Applying a voltage above 1.2 V to SHD pin will enable the device for normal operation. The device will go through soft−start to normal operation. Thermal Shutdown Internal Thermal Shutdown circuitry is provided to protect the integrated circuit in the event that the maximum junction temperature is exceeded. If the junction temperature exceeds 160 °C, the device shuts down. In this mode switch Q1 and Q2 and the control circuits are all turned off. The device restarts in soft−start after the temperature drops below 135 _C. This feature is provided to prevent catastrophic failures from accidental device overheating and it is not intended as a substitute for proper heatsinking. |
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