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NCP3133A Datasheet(PDF) 10 Page - ON Semiconductor |
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NCP3133A Datasheet(HTML) 10 Page - ON Semiconductor |
10 / 13 page NCP3133A http://onsemi.com 10 DETAILED DESCRIPTION Overview NCP3133A is a low input voltage 3 A high performance synchronous buck converter with two integrated N−MOSFETs. NCP3133A’s output voltage range is from 0.6 V to 0.84 x Vin and it has wide input voltage range from 2.9 V to 5.5 V. The features of NCP3133A include supporting pre−bias start−up to protect sensitive loads, cycle−by−cycle over−current limiting and short circuit protection, power good monitor, over voltage and under voltage protection, built in output discharge and thermal shutdown. NCP3133A provides two operation modes to fit various application requirements. The automatic CCM/DCM mode operation provides reduced power loss and increases the efficiency at light load. The adaptive power control architecture enables smooth transition between light load and heavy load while maintaining fast response to load transients . Operation Mode NCP3133A offers two operation modes programmed by PS pin connections, see table below. Table 5. PS pin Connection Operation Mode Auto Skip at Light Load ( ≤)174 kW to GND Automatic CCM/DCM Yes Floating or pulled to VDD FCCM In forced continuous conduction mode (FCCM), the high−side FET is ON during the on−time and the low−side FET is ON during the off−time. The switching is synchronized to an internal clock thus the switching frequency is fixed. In Automatic CCM/DCM mode, the high−side FET is ON during the on−time and low−side FET is ON during the off−time until the inductor current reaches zero. An internal zero−crossing comparator detects the zero crossing of the inductor current from positive to negative. When the inductor current reaches zero, the comparator sends a signal to the logic circuitry and turns off the low−side FET. When the load is increased, the inductor current is always positive and the zero−crossing comparator does not send any zero−crossing signal. The converter enters into continuous conduction mode (CCM) when no zero−crossing is detected for two consecutive PWM pulses. In CCM mode, the switching synchronizes to the internal clock and the switching frequency is fixed. Reference Voltage The NCP3133A incorporates 600 mV reference voltage with 1.0 % tolerance. Internal Soft−Start To limit the start−up inrush current, an internal soft start circuit is used to ramp up the reference voltage from 0 V to its final value linearly. The internal soft start time is 0.4 ms typically. Soft Stop Soft−Stop or discharge mode is always on during faults or disable. In this mode, a fault (UVP, OCP) or disable (EN) causes the output to be discharged through an internal 2 0 W transistor inside of SW terminal. The time constant of soft−stop is a function of output capacitance and the resistance of the discharge transistor. Automatic Power Saving Mode In Automatic CCM/DCM mode when the load current decreases, the converter will enter power saving mode operation. During power saving mode, the low−side MOSFET will turn off when the inductor current reaches zero. So the converter skips switching and operates with reduced frequency , which minimizes the quiescent current and maintains high efficiency. Forced Continuous Conduction Mode When PS pin is floating or pulled high, NCP3133A is operating in forced continuous conduction mode in both light load and heavy load conditions. In this mode, the switching frequency remains constant over the entire load range, making it suitable for applications that need tight regulation of switching frequency at a cost of lower efficiency at light load. |
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